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Ruthenium(II) complexes bearing polypyridyl ligands with amide bound thienyl groups for photochemical… Majewski, Marek B. 2013

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RUTHENIUM(II) COMPLEXES BEARING POLYPYRIDYL LIGANDS WITH AMIDE BOUND THIENYL GROUPS FOR PHOTOCHEMICAL ENERGY CONVERSION   by  Marek B. Majewski  BSc. Chemistry, University of Saskatchewan, 2007     A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of  DOCTOR OF PHILOSOPHY  in  The Faculty of Graduate Studies  (CHEMISTRY)     THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) MARCH 2013  © Marek B. Majewski, 2013   ii  ABSTRACT  Mimicking natural photosynthesis requires long charge recombination lifetimes, spatial charge separation, and sufficient excited state energy to catalyze processes such as water splitting. Complexes bearing laminate acceptor ligands and ancillary diimine ligands with electron rich donor moieties are suitable candidates as reaction centers for photoinduced charge separation in artificial photosynthesis. In this work, new diimine ligands with thiophene oligomers appended via amide linkages are incorporated into metal polypyridyl complexes. Homoleptic Ru2+ complexes bearing 1,10- phenanthroline ligands with amide bound bithiophene units exhibit excited state behavior deviating significantly from that observed in [Ru(phen)3][PF6]2 (30). The bithiophene unit fuels a long-lived excited state (τ ≈ 7 μs) in [Ru(phen-btL)3][PF6]2 (32) through an energy reservoir effect, where 3LC and 3MLCT states are equilibrating in the excited state. A third 3ILCT state is found to equilibrate with the aforementioned states giving a rare three-state equilibrium where the third state is a charge separated state storing ΔG° ≥ 1.9 eV of energy.  In order to introduce an aspect of vectorial charge separation into donor-chromophore- acceptor triads, 1,10-phenanthroline ligands bearing bithiophene moieties are introduced as donor ligands into Ru2+-based triads with laminate polypyridyl acceptor ligands; dipyrido[3,2- a:2',3'-c]phenazine (dppz), tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz), and 9,11,20,22-tetraazatetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3''']-pentacene (tatpp). Triads incorporating bithiophene amide diimine ligands and laminate acceptor ligands (50-52) have long-lived charge separated excited states (τes = 2.2 – 7.0 μs), where an electron is localized on the central portion of the acceptor ligand. Charge separated excited states in these triads transiently store an appreciable amount of energy (ΔG° ≈ 0.98 – 1.41 eV).  iii  PREFACE  In all chapters, Prof. Michael O. Wolf acted in a supervisory role. Chapters 2 and 3 involved collaboration with Prof. Frederick M. MacDonnell and Dr. Norma de Tacconi at the University of Texas, Arlington, U.S.A.  Portions of Chapters 2 have been published previously, and I am the principal author of this work. I carried out all of the work in this chapter, with the exception of the spectroelectrochemical and electrochemical measurements which were performed by Dr. Norma de Tacconi. Cyclometalated Ir3+ complexes 42-44 were prepared by Ashlee Howarth at the University of British Columbia. Portions of Chapter 3 have been accepted for publication. I am the principal author of this work, and carried out all of the experiments with the exception of the spectroelectrochemical and electrochemical experiments (as noted) that were performed by Dr. Norma de Tacconi.  I am the principal author of the work in Chapter 4. Crystal structures of complexes 85-88 were determined by Dr. Brian Patrick at the University of British Columbia.  Publications arising from this work:  Majewski, M. B.; de Tacconi, N. R.; MacDonnell, F. M.; Wolf, M. O. Chem. Eur J. 2013, in press. Majewski, M. B.; de Tacconi, N. R.; MacDonnell, F. M.; Wolf, M. O. Inorg. Chem. 2011, 50, 9939.   iv  TABLE OF CONTENTS  Abstract ...................................................................................................................................... ii Preface....................................................................................................................................... iii Table of Contents ....................................................................................................................... iv List of Tables ........................................................................................................................... vii List of Figures ......................................................................................................................... viii List of Symbols and Abbreviations.......................................................................................... xiv List of Charts............................................................................................................................. xx List of Equations ...................................................................................................................... xxi List of Schemes ...................................................................................................................... xxii Acknowledgements ............................................................................................................... xxiii Dedication .............................................................................................................................. xxiv   CHAPTER 1 – Introduction....................................................................................................... 1 Section 1.1 – Overview  ....................................................................................................... 1 Section 1.2 – Artificial photosynthesis ................................................................................ 2 Section 1.2.1 - Light absorption and the properties of Ru(II) polypyridyl complexes ... 5 Section 1.2.2 - Assemblies for vectorial electron transfer .............................................. 9 Section 1.3 - Extending the lifetime of charge separated states with energy reservoirs .... 15 Section 1.4 – Oligo- and polythiophenes ........................................................................... 21 Section 1.4.1 – Metal complexes bearing oligothiophenes ........................................... 23 Section 1.5 – Overview of transient absorption spectroscopy ........................................... 26 Section 1.6 – Goals and scope ........................................................................................... 29  CHAPTER 2 - Ligand-triplet-fueled, long-lived, charge separation in Ru(II) complexes with bithienyl-functionalized ligands ........................................................................................ 31 Section 2.1 – Introduction .................................................................................................. 31 Section 2.2 – Experimental  ............................................................................................... 34 Section 2.2.1 – General ................................................................................................. 34 Section 2.2.2 – Methods for collection emission lifetime and transient absorption  data ................................................................................................................................ 36 Section 2.2.3 – Methods ................................................................................................ 38 v  Section 2.3 – Results and discussion ................................................................................. 43 Section 2.3.1 – Synthesis and characterization ............................................................. 43 Section 2.3.2 – Photophysical properties ...................................................................... 45 Section 2.3.3 – Effect of longer conjugation length in ligands ..................................... 58 Section 2.3.4 – Electropolymerization of complexes bearing peripheral bithienyl moieties ............................................................................................. 60 Section 2.3.5 – Incorporation of oligothiophene ligands into cyclometalated Ir(III) complexes ......................................................................................... 63 Section 2.4 – Conclusions .................................................................................................. 67  CHAPTER 3 – Long-lived, directional photoinduced charge separation in Ru(II) complexes bearing laminate polypyridyl ligands ................................................................................ 69 Section 3.1 – Introduction  ................................................................................................. 69 Section 3.2 – Experimental  ............................................................................................... 72 Section 3.2.1 – General  ................................................................................................ 72 Section 3.2.2 – General procedures for preparation of organic precursors required for  the synthesis of metal complexes bearing dppz, tpphz and tatpp ligands ............................................................................................... 74 Section 3.2.3 – Methods  ............................................................................................... 75 Section 3.3 – Results and discussion ................................................................................. 79 Section 3.3.1 – Synthesis and characterization ............................................................. 79 Section 3.3.2 – Electrochemical evaluation .................................................................. 84 Section 3.3.3 – Ground state optical properties  ........................................................... 87 Section 3.3.4 – Excited state properties  ....................................................................... 90 Section 3.3.5 – Effect of Zn2+ coordination and solvent environment in unsubstituted tatpp complexes ................................................................................ 95 Section 3.3.6 – Zn2+ coordination and bithiophene effects in tpphz complexes  .......... 98 Section 3.3.7 – Zn2+ coordination effects and the influence of bithienyl moieties in substituted tatpp complexes ............................................................ 103 Section 3.3.8 – The photophysical properties of a directly bound, 2,2'-bipyridine [Ru(phen-btL)2(tatpp)][PF6]2 (52) analog ....................................... 108 Section 3.4 – Conclusions  ............................................................................................... 111  vi  CHAPTER 4 – Elucidating the role of amide linkages in Ru(II) complexes bearing thiophene substituted 2,2'-bipyridine ligands ................................................................................... 113 Section 4.1 – Introduction ................................................................................................ 113 Section 4.2 – Experimental  ............................................................................................. 116 Section 4.2.1 – General  .............................................................................................. 116 Section 4.2.2 – Methods .............................................................................................. 118 Section 4.2.3 – X-Ray crystallography  ...................................................................... 125 Section 4.3 – Results and discussion ............................................................................... 129 Section 4.3.1 – Synthesis and characterization  .......................................................... 129 Section 4.3.2 – Solid state characterization  ............................................................... 133 Section 4.3.3 – Photophysical properties of complexes 85-90 ................................... 139 Section 4.4 – Conclusions ................................................................................................ 154  CHAPTER 5 – Conclusions and future work ......................................................................... 156 Section 5.1 – Conclusions  ............................................................................................... 156 Section 5.2 – Future work ................................................................................................ 162  References  .............................................................................................................................. 165 Appendix 1 .............................................................................................................................. 177 Appendix 2 – Crystallography data ........................................................................................ 185   vii  LIST OF TABLES  Table 2-1. Select photophysical properties of ligands and complexes presented in this chapter ........................................................................................................................... 48 Table 2-2. Photophysical properties of Ir3+ complexes with oligothiophene ligands .............. 65 Table 3-1. Redox potentials for the oxidation (Eox) and reduction (Ered) of 30, 32, 50-54, 65-68. ............................................................................................................................ 86 Table 3-2. Summary of photophysical properties of complexes reported in this chapter ........ 93 Table 4-1. Selected bond lengths and angles for [Ru(bpy)2(tL)][PF6]2 (85) .......................... 134 Table 4-2. Selected bond lengths and angles for [Ru(bpy)2(btL)][PF6]2 (86) ........................ 135 Table 4-3. Selected bond lengths and angles for [Ru(bpy)2(sec-amL)][PF6]2 (87)  .............. 136 Table 4-4. Selected bond lengths, angles and C-H▪▪▪F contacts for [Ru(bpy)2(tert- amL)][PF6]2 (88)  ........................................................................................................ 138 Table 4-5. Selected photophysical and electrochemical properties of the complexes described in this chapter .............................................................................................. 142 Table A2-1. Selected crystal structure data for [Ru(bpy)2(tL)][PF6]2 (85) and [Ru(bpy)2(btL)][PF6]2 (86) .......................................................................................... 183 Table A2-2. Selected crystal structure data for [Ru(bpy)2(sec-amL)][PF6]2 (87) and [Ru(bpy)2(tert-amL)][PF6]2 (88) ................................................................................. 184    viii  LIST OF FIGURES  Figure 1-1. A general representation of artificial photosynthesis. Illustrated is the series of electron transfer/energy transfer events that occur after light absorption. The abbreviations used here are: D = electron transfer donor, A = electron transfer acceptor, catox = O2 evolving catalyst, catred = H2 evolving catalyst. Vectorial and long range charge separation is achieved by bracketing the chromophore with electron donor and acceptor moieties that serve to shuttle charges to catalytic termini. Adapted from ref. 5 .......................................................................................... 4 Figure 1-2. A simplified diagram illustrating possible excited state transitions in [Ru(bpy)3] 2+ (1). Adapted from ref. 20 .......................................................................... 6 Figure 1-3. A simplified Jablonski diagram representing the relative energy levels of the excited state manifold in [Ru(bpy)3] 2+ (1). Dashed arrows represent nonradiative decay processes, while solid arrows represent excitation and emissive relaxation processes. Adapted from refs. 19,20 ................................................................................ 8 Figure 1-4. Jablonski diagram for a bichromophoric system with 3MLCT and 3LC states of nearly the same energy. Dashed arrows to the ground state represent nonradiative decay pathways. Adapted from ref. 56 ........................................................................ 17 Figure 1-6. (left) Complex 18 and (right) a Jablonski diagram illustrating the relevant lowest lying states in complex 18 and their equilibria. Adapted from ref. 65 ............. 20 Figure 1-7. Simplified band diagram for oligo- and polythiophene. Shown are the expected changes between HOMO-LUMO levels on increasing the chain length. Adapted from ref. 66 .................................................................................................................. 22 Figure 2-1. Normalized absorption spectra of ligands 27-29 (CH3CN).  ................................ 46 Figure 2-2. Absorption and emission spectra of complexes 31-33 (CH3CN, λex = 450 nm). .. 47 Figure 2-3. Excited state difference spectra of [Ru(phen-tL)3][PF6]2 (31, black), [Ru(phen- btL)3][PF6]2 (32, teal), [Ru(phen)2(phen-btL)][PF6]2 (33, blue) and [Ru(phen)3][PF6]2 (30, red); t = 65 – 265 ns (CH3CN, λex = 355 nm, fwhm = 35 ps). 48 Figure 2-4. Excited state difference spectra of [Ru(phen-tL)3][PF6]2 (31, black) and [Ru(phen-btL)3][PF6]2 (32, red); t = 5 – 6 ns (CH3CN, λex = 355 nm, fwhm = 35 ps).49 Figure 2-5. A high resolution TA difference spectrum of complex 32 (CH3CN, t = 0 – 2 μs, λex = 355 nm, fwhm = 35 ps, grating = 150 g/mm).  ................................................... 50 Figure 2-6. Normalized TA difference spectra for [Ru(phen-btL)3][PF6]2 (32) and phen-btL (28). (CH3CN, λex = 355 nm, fwhm = 35 ps) .............................................................. 52 Figure 2-7. Reductive spectroelectrochemistry of [Ru(phen-btL)3][PF6]2 (32, -0.85 V, 50 μM solution in CH3CN, black), and differential excited state spectrum of [Ru(phen- btL)3][PF6]2 (32, red); t = 0 – 2 μs (CH3CN, λex = 355 nm, fwhm = 35 ps). ............... 54 ix  Figure 2-8. Chemical oxidation of phen-btL (28) with increasing amounts of NOPF6 in CH3CN. ....................................................................................................................... 55 Figure 2-9. Differential absorption spectra of [Ru(phen-btL)3][PF6]2 (32) in the presence of TTF, illustrating decreases in absorption in the 400-450 nm region up to 2 μs after excitation (CH3CN, λex = 355 nm, fwhm = 35 ps). ..................................................... 56 Figure 2-10. (a) TA spectra of [Ru(phen-btL)3][PF6]2 (32) in the presence of MV 2+, up to 2 μs after excitation. Pictured is the bleaching of the bands corresponding to the excited state 32 species concomitant with growth of  bands corresponding to the formation of MV▪+ at 400 nm and 600 nm.112 (λex = 355 nm) (b) Ground state absorption spectrum of 32 (CH3CN) in the presence of an excess of MV 2+ before laser irradiation at 355 nm (black), and after irradiation (red). Bands at 400 nm, and 600 nm correspond to the reduced MV▪+ species.112 .................................................. 57 Figure 2-11. Jablonski diagram of [Ru(phen-btL)3][PF6]2 (32) in CH3CN. ............................ 58 Figure 2-12. (a) Absorption spectrum of [Ru(phen)2(phen-ttL)][PF6]2 (34). (b) TA difference spectrum of 34 (CH3CN, λex = 355 nm, fwhm = 35 ps). ............................ 59 Figure 2-13. (a) Cyclic voltammogram showing the increase in current with successive scans of a CH3CN solution of [Ru(phen-btL)3][PF6]2 (32). (b) Absorption spectra of a solution of 32 (CH3CN) and a 10 scan film of poly-32 on an ITO substrate. .......... 60 Figure 2-14. Solid-state excited state TA spectra of unfunctionalized ITO (red) and poly-32 (t = 0 - 200 ns, CH3CN, λex = 355 nm, fwhm = 35 ps). ............................................... 61 Figure 2-15. SEM micrographs of 15 scan electrochemically grown films of (a) [Ru(phen- btL)3][PF6]2 (32) and (b) [Ru(phen-btL)2(dppz)][PF6]2 (50) on an ITO substrate. .... 62 Figure 2-16. Chronoamperometry experiment with (a) poly-32 and (b) poly-50 in CH3CN with 0.1 M n-[Bu4N]PF6 (on an ITO substrate) with UV-light irradiation (λem = 365 nm, 0 V vs. Ag wire). ................................................................................................. 63 Figure 2-17. Normalized absorption spectra of Ir3+ complexes 42-44 (CH3CN). ................... 65 Figure 2-18. TA difference spectra of cyclometalated Ir3+ complexes 42-44 (t = 78 – 127 ns, CH3CN, λex = 355 nm, fwhm = 35 ps). ....................................................................... 66 Figure 3-1. (top) Portion of the 1H NMR spectrum of [Ru(phen-btL)2(tatpp)][PF6]2 (52) prior to addition of Zn2+ and (bottom) portion of the 1H NMR spectrum of 52 with 5 eq. of Zn2+ (CD3CN, 400 MHz, 24.9°C). ................................................................... 83 Figure 3-2. TEM micrographs of (a) [Ru(phen-btL)2(tatpp)][PF6]2 (52) with 5 eq. Zn 2+ and (b) 52 without Zn2+ cast from CH3CN. Vacc = 80.0 kV. ............................................. 84 Figure 3-3. Schematic comparison of the redox potentials of the reported complexes; Ru2+/3+ oxidation (filled circles), bithienyl oxidation (unfilled circles), ligand based reductions associated with the distal (redox) MO (squares) and proximal (optical) MO (triangles). ........................................................................................................... 85 x  Figure 3-4. Absorbance spectra of complexes 50-52 in CH3CN. ............................................ 87 Figure 3-5. (a) Normalized absorbance spectra of [Ru(phen)2(tpphz)][PF6]2 (53) and [Ru(phen-btL)2(tpphz)][PF6]2 (51), and (b) complexes [Ru(phen)2(tatpp)][PF6]2 (54) and [Ru(phen-btL)2(tatpp)][PF6]2 (52) in CH3CN. ..................................................... 88 Figure 3-6. Absorbance spectra of (a) [Ru(phen-btL)2(tpphz)][PF6]2 (51) and (b) [Ru(phen- btL)2(tatpp)][PF6]2 (52) with and without 5 eq. of Zn 2+ as Zn(OTf)2 in CH3CN. ...... 90 Figure 3-7. Emission spectra for (a) [Ru(phen-btL)2(tpphz)][PF6]2 (51) in the absence (blue) and presence (orange) of Zn2+ as Zn(OTf)2 and (b) the same spectra collected after purging the sample with Ar for 15 minutes (λex = 450 nm, CH3CN). ........................ 92 Figure 3-8. TA difference spectra of 50-52 in CH3CN (t = 0.78 – 1.28 µs, λex = 355 nm, fwhm = 35 ps).............................................................................................................. 94 Figure 3-9. Qualitative Jablonski diagrams of 66 (left) in CH3CN or CH2Cl2 and [Ru(phen)2(tatpp)][PF6]2 (54, right) in CH3CN.  On the left, the red and blue highlights are used to show how the 3MLCTdist is perturbed by the solvent, CH2Cl2 (red) or CH3CN (blue).  On the right, the red and blue highlights are used to show how the 3MLCTdist is perturbed by the presence (blue) or absence (red) of Zn 2+.  States in black are less significantly influenced by the solvent or Zn.  Dashed arrows are used to indicate non-radiative decay pathways. ........................................ 95 Figure 3-10. Normalized TA difference spectrum of [Ru(phen)2(tatpp)][PF6]2 (54) and ‘Zn(tatpp)Zn’ (67) adduct in CH3CN (λex = 355 nm, fwhm = 35 ps). ........................ 97 Figure 3-11. (a) TA difference spectra of [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen)2(tpphz)][PF6]2 (53, t = 551 – 1048 ns); (b) TA difference spectra of [Ru(phen-btL)2(tpphz)][PF6]2 (51Zn) and [Ru(phen)2(tpphz)][PF6]2 (53Zn) in the presence of 5 eq. Zn2+ (t = 61 – 111 ns). (CH3CN, λex = 355 nm, fwhm = 35 ps) ...... 98 Figure 3-12. Qualitative Jablonski diagrams of [Ru(phen)2(tpphz)][PF6]2 (53, left) in CH3CN and [Ru(phen-btL)2(tpphz)][PF6]2 (51, right) in CH3CN.  In both diagrams, the red and blue highlights are used to show how the 3MLCTdist is perturbed through the addition (blue) or lack (red) of Zn2+. States in black are less significantly influenced by the Zn2+ ion. .................................................................. 100 Figure 3-13. (a) TA spectra of the ‘Zn(tatpp)Zn’ (67) adduct (red, t ≈ 1 µs), 52 (blue, t = 456 – 647 ns) and 52Zn (t = 61 – 111 ns); (b) Reductive SEC of 52 (orange, -0.9 V) and TA difference spectra of 52 (blue, t = 456 – 647 ns) and 54 (green, t = 43 – 243 ns). (CH3CN, λex = 355 nm, fwhm = 35 ps) .............................................................. 103 Figure 3-14. Qualitative Jablonski diagrams of [Ru(phen-btL)2(tpphz)][PF6]2 (52) and 52Zn in CH3CN.  The red and blue highlights are used to show which states are most perturbed by the presence or absence of Zn2+.  A blue highlight shows the relative energy level of a state in the presence of Zn2+ whereas red shows where the states xi  reside in the absence of Zn2+.  States in black are less significantly influenced by the Zn2+ ion. Dashed arrows are used to indicate non-radiative decay pathways. ... 105 Figure 3-15. (a) Ground state absorption spectrum of [Ru(tL)2(tatpp)][PF6]2 (64) and (b) transient absorption difference spectrum (shown with decay) of 64 (CH3CN, λex = 355, fwhm = 35 ps). .................................................................................................. 109 Figure 4-1. A chromophore-amide-catalyst dyad reported by Meyer et al. .......................... 113 Figure 4-2. Solid state structure of [Ru(bpy)2(tL)][PF6]2 (85). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity. .................................................................................................... 133 Figure 4-3. Solid state structure of [Ru(bpy)2(btL)][PF6]2 (86). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity. .................................................................................................... 134 Figure 4-4. Solid state structure of [Ru(bpy)2(sec-amL)][PF6]2 (87). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity. ................................................................................... 136 Figure 4-5. Solid state structure of [Ru(bpy)2(tert-amL)][PF6]2 (88, left) and the same structure with one associated [PF6] - counterion and some possible C-H▪▪▪F contacts shown. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms and occluded solvent molecules omitted for clarity. ....................................................... 138 Figure 4-6. (a) Absorption and emission spectra for [Ru(bpy)3][PF6]2 (1), [Ru(bpy)2(tL)][PF6]2 (85),  [Ru(bpy)2(sec-amL)][PF6]2 (87),  [Ru(bpy)2(tert- amL)][PF6]2 (88), and (b) absorption and emission spectra for [Ru(bpy)3][PF6]2 (1) and [Ru(bpy)2(btL)][PF6]2 (86) in CH3CN (λex = 450 – 490 nm). ............................ 139 Figure 4-7. Transient absorption difference spectra of complexes [Ru(bpy)2(sec- amL)][PF6]2 (87) (a), [Ru(bpy)2(tert-amL)][PF6]2 (88) (b), [Ru(bpy)2(tL)][PF6]2 (85) (c) in CH3CN (λex = 355 nm, fwhm = 35 ps). .................................................... 146 Figure 4-8. TA difference spectra comparing [Ru(bpy)2(tL)][PF6]2 (85, blue), [Ru(bpy)2(sec-amL)][PF6]2 (87, black), [Ru(bpy)2(tert-amL)][PF6]2 (88, red) and [Ru(bpy)3][PF6]2 (1, teal) in CH3CN (λex = 355 nm). ............................................... 148 Figure 4-9. TA difference spectra of (a) [Ru(bpy)2(btL)][PF6]2 (86) and (b) [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(btL)][PF6]2 (86) and [Ru(bpy)3][PF6]2 (1) in CH3CN (λex = 355 nm, fwhm = 35 ps). ..................................................................... 149 Figure 4-10. Emission and absorption spectra of [Ru(tL)3][PF6]2 (89), [Ru(sec-amL)3][PF6]2 (90) and [Ru(bpy)3][PF6]2 (1) in CH3CN (λex = 490 nm). ........................................ 150 Figure 4-11. Comparison of extended TA difference spectra of complexes [Ru(tL)3][PF6]2 (89, red) and [Ru(sec-amL)3][PF6]2 (90, black) (t = 0 – 50 ns, CH3CN, λex = 355 nm, fwhm = 35 ps). ................................................................................................... 152 xii  Figure 4-12. (a) Excited state spectra of [Ru(sec-amL)3][PF6]2 (90) in the presence of MV 2+ (~1 mM) and (b) in the presence of TTF (~0.6 μM) in CH3CN (t = 0 -50 ns, λex = 355 nm, fwhm = 35 ps). ............................................................................................ 153 Figure A1-1. Normalized absorbance spectra of [Ru(phen)3][PF6]2 (30, black), [Ru(phen- tL)3][PF6]2 (31, blue), [Ru(phen-btL)3][PF6]2 (32, teal), [Ru(phen)2(phen- btL)][PF6]2 (33, red). ................................................................................................. 177 Figure A1-2. Time resolved transient absorption decay curve of [Ru(phen-tL)3][PF6]2 (32) with monoexponential fit shown in red (410 – 480 nm). ......................................... 177 Figure A1-3. Time resolved transient absorption decay curves of [Ru(phen-btL)3][PF6]2 (32) at various wavelengths with monoexponential fits shown in black and red............. 178 Figure A1-4. Time resolved transient absorption decay curves of [Ru(phen)2(phen- btL)][PF6]2 (33) at various wavelengths with monoexponential fits shown in black and red. ..................................................................................................................... 179 Figure A1-5. Transient absorption difference spectrum of [Ru(phen-btL)3][PF6]2 (32) 200 ns after excitation at 450 nm (black) and 355 nm (red). ............................................... 179 Figure A1-6. DPV - Reduction (top) and oxidation (bottom) of 200 M [Ru(phen- btL)3][PF6]2 (32) in CH3CN containing n-[Bu4N]PF6 (0.1 M) using a GC disk electrode (1 mm diameter). Voltammograms were obtained with two different negative potential limits. DPV parameters: Potential pulse amplitude = 0.05 V, step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V.................................. 180 Figure A1-7. Comparison of  DPV for the electroreduction of [Ru(phen-btL)3][PF6]2 (32, red line) and [Ru(phen)3][PF6]2  (30, dashed blue line) in CH3CN containing n- [Bu4N]PF6 (0.1 M) using a Pt disk electrode (105 mm diameter). DPV parameters: Potential pulse amplitude = 0.05 V, step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V.  ............................................................................................... 181 Figure A1-8. DPV - electroreduction (top) and electrooxidation (bottom) of [Ru(phen- tL)3][PF6]2 (32, 50 μM) in CH3CN containing 0.1 M n-[Bu4N]PF6 as supporting electrolyte and using a Pt disk electrode (1 mm diameter). DPV parameters: Potential pulse amplitude = 0.05 V. step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V.................................................................................................. 182 Figure A1-9. Absorption spectra recorded at selected potentials during the electroreduction of [Ru(phen)3][PF6]2 (30, 100 μM) in 0.1 M n-[Bu4N]PF6/CH3CN using progressively negative potentials from 0.0 V to -2.1 V. Working electrode: Pt mesh in capillary cell. ........................................................................................................ 183 Figure A1-10. Difference absorbance spectra, A, during a linear potential cycle involving the electroreduction/electrooxidation of [Ru(tL)2(tatpp)][PF6]2 (64, 160 M) in CH3CN (0.1 M TBAPF6).  Spectra were collected during the negative-going potential scan (top frame) and the subsequent returning scan (bottom frame) at 5 xiii  mV/s in the +0.2 V to -1.1 V potential window.  ITO was used as working electrode and the electrochemical cell was a 4 mm quartz cuvette containing a Pt wire as counter electrode and a miniature Ag/AgCl (non-leak) reference electrode.  .......... 184   xiv  LIST OF SYMBOLS AND ABBREVIATIONS  * excited state A absorbance, acceptor Anh. anhydrous a.u. arbitrary units Anal. analysis BET back electron transfer br broad BT bithiophene bpy 2,2'-bipyridine btL 4,4'-di([2,2'-bithiophen]-5-yl)-2,2'-bipyridine C chromophore C-A chromophore-acceptor CS charge separated CV cyclic voltammetry CCD charge-coupled device Calcd. Calculated Catox O2 evolving catalyst Catred H2 evolving catalyst CCDC Cambridge Crystallographic Data Center CIF crystallographic information file D donor d doublet DQ2+ diquat DSSC dye-sensitized solar cell D-C donor-chromophore D-C-A donor-chromophore-acceptor dppz dipyrido[3,2-a:2',3'-c]phenazine (47) DPV differential pulse voltammetry dadppz dipyrido[3,2-a:2',3'-c]phenazine-11,12-diamine (63) δ chemical shift (ppm) xv  Δ difference, heat DNA deoxyribonucleic acid DMSO dimethyl sulphoxide DMF dimethyl formamide dpb 4,4'-diphenyl-2,2'-bipyridine ET electron transfer ESI-MS electrospray ionization mass spectrometry EI-MS electron impact mass spectrometry EtOH ethanol Et2O diethyl ether ΔEST energy gap between singlet-triplet states EMLCT energy of the MLCT state E0-0 zero-zero spectroscopic energy ES excited state eV electron volts eq. equivalents Eox oxidation potential Ered reduction potential E°ox standard oxidation potential E°red standard reduction potential EDOT 3,4-ethylenedioxythiophene Eg energy gap ΔE energy difference fwhm full width at half maximum FESEM field emission scanning electron microscopy F Faraday constant, structure factor fs femtosecond ΔETG° Gibbs free energy of photoinduced electron transfer ΔG° Gibbs free energy GC glassy carbon g/mm grooves per millimeter GS ground state xvi  h hour h+ hole HPLC high performance liquid chromatography HR-ESI MS high resolution ESI-MS HR-EI MS high resolution EI-MS Hz hertz h Planck’s constant HOMO highest occupied molecular orbital H-donor hydrogen bond donor IL intraligand ILCT interligand charge transfer, intraligand charge transfer IR infrared ITO indium tin oxide J joules, indirect dipole-dipole coupling K kelvin kisc rate constant of intersystem crossing kLC rate constant of decay from the ligand-centered state kLM rate constant of energy transfer from the LC to the MLCT state kMC rate constant of conversion to the metal-centered state kML rate constant of energy transfer from the MLCT to the LC state kr rate constant of radiative decay knr rate constant of non-radiative decay LEC light emitting electrochemical cell LC ligand centered LUMO lowest unoccupied molecular orbital LMCT ligand-to-metal charge transfer LCBT ligand-centered state on bithiophene LCtatpp ligand-centered state on tatpp λ wavelength, reorganization energy λmax wavelength at peak maximum λem wavelength of emission λex wavelength of excitation xvii  M molar MO molecular orbital MLCTprox metal-to-ligand charge transfer to the proximal orbital MLCTdist metal-to-ligand charge transfer to the distal orbital MALDI-TOF matrix assisted laser desorption ionization time of flight MeOH methanol MePTZ 10-methylphenothiazine m/z mass-to-charge ratio μ micro, X-ray linear absorption coefficient mV millivolt ML2L' metal complex with two different ligands (L and L') mol mole mmol millimole mL milliliter mm millimeter MV2+ methyl viologen NADPH nicotinamide adenine dinucleotide phosphate Nd:YAG neodymium-doped yttrium aluminum garnet NDI napththalene diimide NMR nuclear magnetic resonance ν frequency, bond stretching ω angle the X-ray source makes with the crystal OD optical density OLED organic light emitting diode OPV organic photovoltaic P680 pigment 680 phen-btL N-(1,10-phenanthrolin-5-yl)-2,2´-bithiophene-5-carboxamide (28) phen-tL N-(1,10-phenanthrolin-5-yl)-thiophene-2-carboxamide (27) phen-ttL N-(1,10-phenanthrolin-5-yl)-[2,2':5',2''-terthiophene]-5-carboxamide (29) PNI 4-(1-piperidinyl)naphthalene-1,8-dicarboximide PTI Photon Technology International PTZ phenothiazine xviii  ppz 1-phenylpyrazole PSI photosystem I PSII photosystem II phen 1,10-phenanthroline Φem quantum yield of emission ppm parts per million ϕ X-ray rotation axis PES photoelectrochemical synthesis Ref. reference RT room temperature R linear regression goodness of fit, residual factor satd saturated s singlet SCE saturated calomel electrode SEC spectroelectrochemical SAM self-assembled monolayer sec-amL N,N'-([2,2'-bipyridine]-4,4'-diyl)bis(thiophene-2-carboxamide) (83) t time delay, triplet TEA triethylamine TA transient absorption tatpp 9,11,20,22-tetraazatetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3''']-pentacene (49) tpphz tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (48) tL 4,4'-di(thiophen-2-yl)-2,2'-bipyridine (77) TEM transmission electron microscopy τ lifetime τem emission lifetime τes excited state lifetime TLC thin layer chromatography tert-amL N,N'-([2,2'-bipyridine]-4,4'-diyl)bis(N-ethylthiophene-2- carboxamide) (84) TTF tetrathiafulvalene UV ultraviolet xix  Vis visible V volts Vacc accelerating voltage WE working electrode Z  number of molecules in a crystallographic unit cell   xx  LIST OF CHARTS  Chart 1-1. Ref. 19,22,23 ................................................................................................................. 6 Chart 1-2. Ref. 38,39 .................................................................................................................. 10 Chart 1-3. Ref. 40-43 .................................................................................................................. 11 Chart 1-4. Ref. 52...................................................................................................................... 13 Chart 1-5. Ref. 59-64 .................................................................................................................. 18 Chart 1-6.  ................................................................................................................................ 21 Chart 1-7. Ref. 73-78 .................................................................................................................. 24 Chart 2-1. Ref. 89-91 .................................................................................................................. 32 Chart 2-2.  ................................................................................................................................ 33 Chart 2-3. ................................................................................................................................. 64 Chart 3-1. Ref. 126,134,135 ........................................................................................................... 70 Chart 3-2.  ................................................................................................................................ 71 Chart 3-3. ............................................................................................................................... 108 Chart 4-1. Ref. 93,186 ............................................................................................................... 115    xxi  LIST OF EQUATIONS  Equation 1-1 .............................................................................................................................. 7 Equation 1-2 .............................................................................................................................. 7 Equation 1-3 .............................................................................................................................. 8 Equation 4-1 .......................................................................................................................... 142 Equation 4-2 .......................................................................................................................... 142    xxii  LIST OF SCHEMES  Scheme 1-1 ................................................................................................................................. 3 Scheme 2-1 ............................................................................................................................... 44 Scheme 2-2 ............................................................................................................................... 44 Scheme 2-3 ............................................................................................................................... 45 Scheme 3-1 ............................................................................................................................... 75 Scheme 3-2 ............................................................................................................................... 79 Scheme 3-3 ............................................................................................................................... 81 Scheme 3-4 ............................................................................................................................... 82 Scheme 3-5 ............................................................................................................................... 82 Scheme 3-6 ............................................................................................................................. 110 Scheme 4-1 ............................................................................................................................. 130 Scheme 4-2 ............................................................................................................................. 131 Scheme 4-3 ............................................................................................................................. 132 Scheme 5-1 ............................................................................................................................. 159    xxiii  ACKNOWLEDGEMENTS  There are a number of people without whom this thesis would not have been possible. I’d like to thank Mike Wolf, the boss, for all of his support and guidance. The many scientific (and otherwise) conversations and video conferences were instrumental in helping me understand the material presented in this work. An emphatic thank-you to Fred MacDonnell and Norma de Tacconi is also in order. Without the extensive Skype chats and back-and-forth email threads, most of the work discussed in this thesis wouldn’t have seen the light of day. Over the past 5 years I’ve had the good fortune of working with too many excellent collaborators to list, and I thank all of them. Dr. Saeid Kamal at LASIR was critical to the success of much of this work, through his tireless troubleshooting and instruction on the many uses of lasers. I was also fortunate to work with two talented undergrads; Simeon Benedikt- Burgenmeister and Jeremy Smith, whose work laid the foundation for Chapter 4 of this thesis.  I’d also like to thank all of the members of the Wolf group (past and present) for the good times. Special thanks to Tim Kelly, Matt Roberts, Glen Bremner, Angela Kuchison, Tamara Kunz and Agostino Pietrangelo for getting me started, and teaching me the ropes of life in the lab, as well as providing much needed moral support in the wilderness, and at the pub. A big high-five to all of my pole whackin’ ski buddies; Shaw, Xavier, Shopsy, Frischmann, Matt, Austin, JP, etc. You guys almost killed me a few times, but it was certainly worth it; many great memories from life in the mountains. A big hug and kiss for Ashlee, who made these last years in Vancouver so worthwhile. Without your ever-present smile and perky upbeat disposition, depression and boredom were a real possibility. Many great years lie ahead, and I’m looking forward to all of them. Finally, without my family, none of this would’ve come together. Mamie i Tacie, dziękuje za wsparcie. Bez inspiracyjnych 'pep talks' Taty, Mamy ‘texting updates’ i emails od Babci, nie wiem jak ta cała impreza by wypadła. Kasia jest najlepszą siostrą jaką brat może mieć. Moja kochana rodzinka.   xxiv     dla Mamy i Taty bez was to by się nie udało      1  CHAPTER 1  Introduction  Section 1.1 – Overview  In 2008 total global energy use was reported to be 532 × 1018 J.1 Approximately 50% of that total energy use came from nations not belonging to the Organization for Economic Cooperation and Development (non-OECD). By 2020 this consumption is projected to grow to 653 × 1018 J, with the majority of the consumption growth coming from non-OECD countries (where demand is often driven by long-term economic growth).1  In the U.S., in 2011, 82% of this energy consumption was satisfied through combustion of fossil fuels, 8% through nuclear electric power, and only 9% through renewable or alternate sources (such as wind, hydroelectric, biofuels, and solar/photovoltaic which accounts for only 2% of alternate sources).2  Although estimates for the exhaustion of global fossil fuel supplies vary, it is clear that this resource is finite, and with current population growth, alternate fuel sources (preferably affordable, efficient and carbon neutral) are needed.3 It is estimated that the sun irradiates the earth with 1022 J of solar energy each day, satisfying the total annual global energy requirement in just a few hours.4 For many years, scientists have grappled with how to best harness this energy on two frontiers: conversion of solar radiation to usable energy (capture), and storage (a very important facet of the problem, due to the diurnal nature of the sun). In nature, plants and other photosynthetic organisms convert sunlight to high-energy chemicals through the concerted multistep process of photosynthesis. Artificial photosynthesis seeks to mimic this natural process, ultimately leading to the storage of energy in chemical bonds and reactive chemical species.5,6 2  Mimicking photosynthesis is a complicated problem, encompassing many different avenues of research. This thesis seeks to expand on one aspect of artificial photosynthesis; the synthesis and photochemistry of metal complexes for application as the primary location of charge separation within the overall “modular” structure of an artificial photosynthetic construct. There are a number of criteria that must be satisfied, in order for these charge separation centers to be useful in artificial photosynthetic applications; light absorption, the formation of long-lived charge separated species, elimination or suppression of competing charge recombination processes, the formation of high energy states, and vectorial or directional charge separation. In this work, the synthesis and photophysical properties of a number of new complexes satisfying these criteria is presented.  Section 1.2 – Artificial photosynthesis  The overarching goal of artificial photosynthesis—formation of high energy chemical species, is a difficult one to achieve, requiring the integration of many chemical functions into a photochemically stable architecture.5-7 Due to the complexity of these architectures, the field of artificial photosynthesis has developed more gradually than other approaches to photochemical energy conversion (such as dye sensitized solar cells).8 Photosynthesis in higher order green plants is composed of a complex reaction scheme where solar energy converts H2O into O2 and some reducing equivalents (in the end: NADPH). 9- 11 These reducing equivalents are used in Photosystem I (PSI) to reduce CO2 to carbohydrates.10,11 In artificial photosynthesis, energy from the sun is used to drive high-energy reactions of small molecules such as water splitting, or CO2 reduction. Recombination of these small molecules results in the recovery of the stored chemical energy. Photocatalytically 3  produced hydrogen and oxygen can be recombined in a fuel cell for electricity production (Scheme 1-1).5  Scheme 1-1   Resolution of the redox reactions of small molecules in artificial photosynthesis into half- reactions provides the foundation for a so-called “modular” approach to artificial photosynthesis;5 where the individual half-reactions are treated separately, and catalysts for these reactions are studied individually. All of these systems, despite compartmentalization of the individual components, require a balance of light absorption, energy/electron transfer and redox catalysis. To this end, most studies have largely been devoted to investigating two families of compounds for these applications: porphyrins and their metallic derivatives, and metal polypyridyl complexes where reactivity is often initiated via metal-to-ligand charge transfer (MLCT) states.5,12-15  In the modular approach to mimic natural photosynthesis, reaction centers or “modules” are linked to create an overall assembly (Figure 1-1). Alstrum-Acevedo, Brennaman, and Meyer have outlined six elements that are required in such an assembly:5 1. Light absorption  2. Electron transfer quenching 3. Redox separation by electron transfer 4. Electron transfer activation of catalyst 5. Multiple electron transfer 6. Reaction of the active catalysts  4   Figure 1-1. A general representation of artificial photosynthesis. Illustrated is the series of electron transfer/energy transfer events that occur after light absorption. The abbreviations used here are: D = electron transfer donor, A = electron transfer acceptor, catox = O2 evolving catalyst, catred = H2 evolving catalyst. Vectorial and long range charge separation is achieved by bracketing the chromophore with electron donor and acceptor moieties that serve to shuttle charges to catalytic termini. Adapted from ref. 5  Within the context of this thesis, elements 1-4 are of particular relevance. In element 1, light absorption can occur either via a single chromophore or through an antenna array (Figure 1.1), with energy-transfer from this array sensitizing the excited state of a chromophore (C → C*). Although they may address the low light absorption of single molecules, preparing antenna complexes is not trivial and has been the subject of many studies.12,16 A detailed discussion of antenna complexes is outside the scope of this thesis, instead light absorption by a single molecule to initiate elements 2-4 is a primary focus. In element 2, a number of different scenarios may take place. A donor-chromophore- acceptor (D-C-A) array or triad may undergo either reductive (D-C*-A → D+-C--A) or oxidative (D-C*-A → D-C+-A-) quenching of the chromophore excited state (C*) to form a charge separated (CS) state.17 In both cases, ΔG must be < 0. The CS state, once formed, may undergo a redox transformation (element 3) that also requires ΔG < 0. This electron transfer may occur in two ways, depending on the nature of element 2; D-C+-A- → D+-C-A- or D+-C--A → D+-C-A-. 5  To obtain redox equivalents D+ and A-, elements 2 and 3 are combined resulting in a free-energy gradient.13,18 Of additional importance is element 4. The potentials of D+/0 and A0/- determine the potential for the individual catalytic reactions (A- activates a H2 evolving catalyst, while D + activates an O2 evolving catalyst). Due to this relationship, overall ΔG° cannot exceed the free energy of the excited state (i.e.: ΔG° ≤ ΔGET°). 5 Thus, the CS state formed in elements 2 and 3 must be of sufficiently high energy to initiate the catalytic reactions occurring at the termini of the artificial photosynthetic complex.  Section 1.2.1 – Light absorption and the properties of Ru(II) polypyridyl complexes  The catalytic reactions occurring in photosynthesis are multi-electron processes, and as such a steady flow of excitation energy is required to drive charge separation, catalysis and to overcome rates of charge recombination. In nature, chlorophyll and carotenoid molecules behave as antennae to satisfy these demands, and as a result incorporating a light harvesting antenna into an artificial photosynthetic structure is desirable.9 However, to study the fundamental processes involved in the formation of charge separated species after photoexcitation, single chromophores may be considered. To date, creating a chromophore that embodies all of the properties needed for artificial photosynthesis (broad spectral absorption, long excited state lifetime, desirable redox potentials, stability, etc.) has proven extremely challenging. Some well-studied chromophores encompassing many of the necessary characteristics are shown in Chart 1-1. Of particular importance is [Ru(bpy)3] 2+ (1), a chromophore that itself, along with many derivatives, has been the central focus of many photophysical studies.19-21 6  Chart 1-1. Ref. 19,22,23   In [Ru(bpy)3] 2+ (1) absorption of light (λmax = 452 nm) originates from an 1MLCT transition. In this transition, an electron is promoted from a Ru dπ orbital (t2g in this complex) to a low-lying π* level on a 2,2'-bipyridine ligand; in effect a 1(dπ6) → 1(dπ5π*) transition.19,20 Relaxation (τ < 1 ps) to a low-lying 3(dπ5π*) triplet state follows.24 A simplified diagram of these processes is shown in Figure 1-2. Other transitions existing in [Ru(bpy)3] 2+ (1) that are activated depending on the oxidation state of the metal and on the nature of the ligands include ligand-to- metal charge transfer (LMCT), metal centered (MC) and ligand centered (LC) transitions.25   Figure 1-2. A simplified diagram illustrating possible excited state transitions in [Ru(bpy)3] 2+ (1). Adapted from ref. 20  7  Formation of the 3MLCT state in [Ru(bpy)3] 2+* (1*) varies the redox properties of [Ru(bpy)3] 2+ (1) by ΔG° = 2.1 eV (equivalent to the emission energy of the 3MLCT state).26 By relating the ground state redox potentials (E°ox = 1.3 V, E°red = -1.3 V vs SCE in CH3CN) to the excited state redox potentials via equations 1-1 and 1-2 (where F is the Faraday constant; 1 eV/V), it is possible to determine that the oxidation potential of [Ru(bpy)3] 2+* ([Ru(bpy)3] 2+* → [Ru(bpy)3] 3+) is -0.8 V (vs. SCE in CH3CN), while the reduction potential is +0.8 V (vs. SCE in CH3CN; [Ru(bpy)3] 2+* → [Ru(bpy)3] +).26,27 It is possible to surmise from these calculations that [Ru(bpy)3] 2+* (1) is capable of oxidizing H2O (E° = -0.76 V at pH 8). 28  E° (ES+/0) = E° (GS+/0) - ΔGES°/F (1-1)  E° (ES0/-) = E° (GS0/-) + ΔGES°/F (1-2) When [Ru(bpy)3] 2+ (1) is excited at λmax = 452 nm, a 1MLCT state is formed. The direction of the transition dipole moment for this state is along the metal to ligand axis. The photoexcited electron is localized on one 2,2'-bipyridine ligand at a time,29 with a hopping rate between the other ligands that is reported to occur on the femtosecond to picosecond time scale.24,30 It has also been reported that initially the excited electron is delocalized between all three ligands, but localizes to one ligand on a femtosecond time scale.31 Conversion of the 1MLCT state to a 3MLCT is rapid (τ ≈ 100 fs) with a quantum yield of formation approaching unity.32,33 Deactivation of the 3MLCT state is temperature dependent, and the lifetime of this state has been reported in many different solvents.34 In H2O the lifetime of the 3MLCT state is 0.6 μs with a quantum yield of emission of 0.04, at room temperature.34 At 77 K, this lifetime increases to 5 μs (in H2O). 19 This temperature dependence is partially due to thermal population of a MC state that decays nonradiatively. Thus, the lifetime of the excited state is given by a sum of the rate of radiative decay (kr), nonradiative decay (knr) and the rate of population of the MC state (kMC) as 8  shown in Figure 1-3. Overall, the relatively long lifetime of the excited state facilitates bimolecular photochemical reactions.  Figure 1-3. A simplified Jablonski diagram representing the relative energy levels of the excited state manifold in [Ru(bpy)3] 2+ (1). Dashed arrows represent nonradiative decay processes, while solid arrows represent excitation and emissive relaxation processes. Adapted from refs. 19,20  Incorporation of substituents onto the polypyridyl ligands can influence the excited state energy of [Ru(bpy)3] 2+ (1). These substituents, based on their properties (electron donating, electron withdrawing, degree of conjugation, etc.) can vary the electron density on the ligand, resulting in a change in the energy of the MLCT transition. There exists a linear relation between the oxidation potential of the metal and the reduction of the ligand corresponding to the energy of the MLCT transition (equation 1-3).20,35  E0-0 (eV) = E°ox - E°red + λ (1-3) In equation 1-3, λ includes contributions from vibrational and solvent reorganization and the difference in Coulombic interaction of the redox states and the MLCT state. From this relationship it is apparent that often the same orbitals involved in the charge transfer transitions are also involved in the redox processes. Vibrational and solvent reorganization processes also play a major role in any photoinduced electron transfer processes that may occur. 9  Combined, all of these properties make [Ru(bpy)3] 2+ (1) a suitable candidate for satisfying elements 1-4, as described by Meyer et al.5 By further tuning the properties of [Ru(bpy)3] 2+ (1) through various ligand substitutions to give larger, more elaborate derivatives these elements may be satisfied to a greater degree resulting in molecular assemblies with functions approaching those of natural photosynthesis.  Section 1.2.2 – Assemblies for vectorial electron transfer  Due to the well-established excited state properties of [Ru(bpy)3] 2+ (1), donor- chromophore-acceptor (D-C-A) triads for vectorial electron transfer in the excited state incorporating [Ru(bpy)3] 2+ (1) chromophores have played a major role in the development of molecular assemblies to mimic photosynthesis. Early examples were realized due to the intermolecular excited state electron transfer demonstrated by solutions of [Ru(bpy)3] 2+ (1) in the presence of electron rich donor molecules such as 10-methylphenothiazine (MePTZ) and electron deficient acceptors such as methylviologen (MV2+) and diquat (DQ2+).36,37 Flash photolysis of these combinations (where it was shown that MV2+ oxidatively quenches [Ru(bpy)3] 2+* (1*), followed by reduction of [Ru(bpy)3] 3+ by MePTZ) led to some of the first examples of D-C-A triads such as those in Chart 1-2.38,39 The triads pictured in Chart 1-2 were found to undergo photoinduced, intramolecular, electron transfer. Using transient absorption spectroscopy (Section 1.5), and monitoring excited state absorption spectra, the growth of bands corresponding to PTZ▪+ and MV▪+ or DQ▪+ was observed.38 From these experiments, rate constants for the formation/decay of these CS states were determined, and complex 4 was found to have a CS lifetime of 165 ns, while the lifetime of 5 varied depending on the arrangement of ligands but was found to be close to that of 4 (τ = 160 10  ns).39 The charge separated states of these two triads were found to store enough energy to perform redox reactions (ΔG° ≈ 1.29 eV; 4, and 1.14 eV; 5). The transfer of electrons to form this CS state is qualitatively analogous to the cascade of electrons occurring in Photosystem II (PSII), where excitation of chlorophyll P680 is followed by electron transfer through a pheophytin to a quinone acceptor. Subsequent reduction of P680+ occurs by electron transfer from a nearby tyrosine residue which is H-bonded to an adjacent histidine residue (and is also positioned near the manganese cluster that catalyses water oxidation).11 Chart 1-2. Ref. 38,39  Although the preparation of the D-C-A triads in Chart 1-2 and a greater understanding of electronic processes in photosystems I and II have come at different periods in time, it is apparent that D-C-A triads (and Ru2+ triads specifically) are good candidates for mimicking the electron transfer processes of photosynthesis. Since the initial studies of 4 and 5, many triads capable of forming CS states have been developed (Chart 1-3).40-43 Triads 6 and 7 take advantage of the excited state reactivity previously observed in PTZ and MV2+ moieties, by employing these fragments as donors and acceptors in triads not based around a Ru2+ chromophore. Triad 6, reported by Elliot et al. is an analog of triads 4 and 5 that 11  uses an earth-abundant metal center.41 The charge separated lifetime observed in triad 6 was comparable to that reported for triads 4 and 5 (τ = 136 ns). Unfortunately, 1,10-phenanthroline complexes of Cu+ undergo Jahn-Teller distortion in the excited MLCT state (due to the Cu2+ character of the metal center), distorting the dihedral angle between the ligands and allowing solvent access to the metal center. Such distortion decreases the lifetime of the excited state by providing a nonradiative decay pathway in the form of solvent coordination.41  Chart 1-3. Ref. 40-43  12  Eisenberg et al. reported the first Pt based triad, 7, to have a CS state lifetime of 230 ns with ca. 1.6 eV of transiently stored energy. In 7, phenothiazine behaves as the donor, while the nitrophenyl group behaves as the acceptor.  Despite the long lifetime, Eisenberg et al. utilized transient absorption measurements to determine that the CS state in 7 was inefficiently formed, as a direct result of competing reactions in both quenching and CS steps.40 Many dyads have also been studied in the context of the formation of CS states, and many have shown promise with respect to the amount of energy their CS states store, and the associated CS excited state lifetimes.12,44,45 Metallosupramolecular dyad 8 is an example where phthalocyanine (a porphyrin derivative) moieties rather than porphyrin moieties are used as termini. On excitation, 8 undergoes electron transfer to form a CS state where an electron is localized on the perylene diimide core (τ = 115 ns). The observed long CS lifetime is attributed to the orthogonal arrangement of chromophores, decreasing the electronic coupling throughout the molecule.42 While 8 is an interesting prospect with respect to being a reaction center in artificial photosynthesis, temporal stabilization of CS states so that they are kinetically able to carry out redox reactions with a catalyst requires a D-C-A triad type arrangement.16 Triad 9 reported by Barigelletti et al. undergoes charge separation via excitation of the terminal protonated porphyrin, with the Au-porphyrin ultimately behaving as the electron acceptor in the final CS state (τ = 3.5 ns).43 Despite the short excited state lifetime of triad 9, porphyrin based D-C-A triads, pentads and higher multicomponent assemblies have been extensively investigated due to the low reorganization energy of electron transfer states localized within the porphyrin.46-50 Albeit outside of the scope of this discussion, it is worth mentioning that Gust et al. have reported a molecular pentad comprised of a porphyrin dyad, a carotenoid polyene, and a diquinone acceptor that undergoes photoinduced electron transfer to ultimately 13  yield a CS state where a hole is localized at one end of the assembly on the carotenoid, while the electron is localized at the other end on a quinone moiety. The lifetime of this state was found to be 55 μs, with a high quantum yield of formation (0.83).51 Chart 1-4. Ref. 52  Hammarström et al. have reported a triad (Chart 1-4, 10), that on photoexcitation of the Ru2+ fragment, rapidly (τ = 40 ns) undergoes electron transfer to the acceptor naphthalene diimide (NDI) units, followed by oxidation of the Mn2+-Mn2+ dimer. This charge separated state has a lifetime that, to date, may be the longest reported lifetime for a CS state originating from a 14  [Ru(bpy)3] 2+ (1) derived system at room temperature (τ = 600 μs).14,52 On cooling to 140 K this lifetime increased to 0.5 s, a lifetime that is on the same time scale as charge recombination in photosynthetic processes in nature.50 Such temperature dependence can be evaluated in the context of Marcus theory, through which Hammarström et al. were able to elucidate a large reorganization energy (λ ≈ 2.0 eV), arising from the shortening of the Mn2+-Mn2+ dimer metal- ligand bonds by an average of 0.2 Å/bond.14,52  In most D-C-A triads, long-lived CS states are attributed to charge recombination processes lying in the Marcus inverted region (where the driving force is larger than the reorganization energy).18 The result is a high-energy CS state with a slow charge recombination rate. In light of such an assessment, the CS state in 10 is surprising. Despite having a relatively high energy content (ΔG° = 1.07 eV),52 the recombination processes fall in the Marcus normal (rather than inverted) regime (λ ≈ 2.0 eV). An explanation for this rests in the fact that Mn2+ complexes are slow electron donors, due to the large reorganization energy accompanying this process in these complexes, and on oxidation this intrinsically large reorganization energy assists in maintaining a long-lived CS state.53 To further mimic natural photosynthetic reaction centers, and due to the long CS lifetime in assemblies bearing Mn2+ clusters, accumulative electron transfer may be possible.54 It is clear that through variation of the donor, acceptor, chromophore and other structural components of D-C-A triads, a range of charge separated state lifetimes can be obtained. These variations influence the driving force for the sequential electron transfer processes; charge separation and charge recombination. Charge separation is a critical first step in photosynthesis, while charge recombination is a significant obstacle on the way to the evolution of efficient energy-storing reactions.  15  Section 1.3 – Extending the lifetime of charge separated states with energy reservoirs  Metal complexes bearing ligands (often aromatic hydrocarbons) with low-lying ligand centered triplet excited states (3LC) have been shown to exhibit phosphorescence originating from the ligand.55 It is also not unusual for complexes bearing ligands with low-lying triplet states to exhibit photophysical behavior arising from the interactions of 3LC and 3MLCT states. In systems where the electronic coupling between the ligand and the metal center is significant, phosphorescence may appear with characteristics of both 3LC and 3MLCT states, while in systems with weak electronic coupling, the two chromophores may interact through energy transfer.56,57 These interactions often lead to an extension of the 3MLCT state lifetime, and as such, incorporating ligands with low-lying 3LC states is one strategy for extending the lifetime of CS states in artificial photosynthetic reaction centers. In order to elucidate the interactions between 3LC and 3MLCT states, it is important to understand the nature of singlet to triplet (and triplet to ground state singlet) decay processes. In general, radiative triplet to singlet ground state processes are influenced by spin-orbit coupling interactions. The role of these spin-orbit coupling interactions is understood in terms of the triplet-singlet transition probability which is proportional to the electric dipole transition moment. The magnitude of the transition moment for triplet to singlet decay is related to two quantities; the magnitude of the spin-orbit operator, and the energy gap between the thermally equilibrated triplet excited state and states in the singlet manifold.56 In this context, it is expected that in aromatic hydrocarbon moieties lacking a heavy atom, the magnitude of the spin-orbit operator is small, resulting in long triplet excited state lifetimes (for example: τ = 0.5 s for pyrene which has an energy gap of ΔEST = 9900 cm -1 between the singlet-triplet states).58  16  From the above discussion, it is possible to rationalize the relatively short (when compared to aromatic hydrocarbons) excited state lifetime of [Ru(bpy)3] 2+ (τ = 0.6 μs, ΔEST = 4500 cm -1).20 It is clear that metal complexes have smaller singlet-triplet energy gaps along with short lifetimes, highlighting the impact that the magnitude of the spin-orbit operator has on the relative rates of the excited state decay processes. Nonradiative relaxation is also influenced by the degree of coupling between the triplet states with higher lying singlet states (S1 or higher). In metal complexes having 3MLCT states the energy gap between the triplet excited state and singlet excited state manifold is smaller resulting in an increase in the magnitude of the transition dipole moment.56,57 In a complex where 3MLCT and 3LC states are weakly interacting and are nearly of the same energy, excitation energy can be disseminated between both states. Aromatic hydrocarbon based 3LC states typically have a larger singlet-triplet energy gap than MLCT states, and it is possible to prepare complexes bearing ligands incorporating aromatic hydrocarbon moieties where an absorption is allowed into both the 1MLCT state (in the visible regime) and the 1LC state (in the UV regime), and where a small energy gap exists between the corresponding two triplet excited states. In this scenario, it is possible to excite into the visible 1MLCT transition that will subsequently undergo intersystem crossing to the 3MLCT state. Relaxation of this state to the ground state will be governed by the magnitude of the rate constants for energy transfer to the 3LC state (Figure 1-4). 17   Figure 1-4. Jablonski diagram for a bichromophoric system with 3MLCT and 3LC states of nearly the same energy. Dashed arrows to the ground state represent nonradiative decay pathways. Adapted from ref. 56  In the scenario shown in Figure 1-4, intersystem crossing occurs from the 1MLCT state exclusively to the 3MLCT state and therefore population of the 3LC state depends entirely on the relative values of kML and kLM. In the case where kML >> kr, the 3MLCT and 3LC states will exist in equilibrium if kLM >> kLC, where kLM depends on the energy difference between the two states. Here, the lifetime of the 3MLCT state is an average of the lifetimes of the two states (as the energy gap between the states becomes larger, the population of the 3MLCT state decreases, while the lifetime increases). Additionally, the rate constant for decay of the equilibrated excited states decreases as the lifetime of the 3LC state increases.56,57 There have been many reports of metal complexes in the literature where equilibration of these two states results in an excited lifetime that is longer than anticipated for excited states arising from a one state, metal based excited state. Some of these complexes are shown in Chart 1-5. Below, it will become clear that the triplet energy levels of states localized on pyrene align well with those of 3MLCT states in Ru2+ complexes; thus the prevalence of ligands incorporating pyrene moieties. 18  Chart 1-5. Ref. 59-64   The first example of the energy or “triplet reservoir” effect observed through the equilibration of 3LC states and 3MLCT states was reported by Ford and Rodgers in complex 11.64 Complex 11 in methanol solution was reported to have a rate constant of reversible energy transfer (kLM) between a 3LC state localized on the pyrene and the 3MLCT state that was a factor of 18 lower than the forward rate of transfer (kML). This equilibration was found to be faster than deactivation processes, resulting in an excited state lifetime of 11.2 μs (much longer than that of [Ru(bpy)3] 2+ 1). Tyson and Castellano reported light-harvesting complex 12, where regardless of excitation wavelength, the complex exhibited emission characteristic of the [Ru(bpy)3] 2+ moiety. The 1LC state localized on pyrene is quantitatively quenched by the MLCT state in this complex resulting in sensitized MLCT-based emission (through an antenna effect).63 In addition, the equilibration of a 3LC state on pyrene and the 3MLCT state resulted in a lifetime of 9.0 μs. Similar behavior 19  was observed by Castellano et al. in complex 16, where through excited state equilibration, the emission (and therefore excited state) lifetime of complex 16 was reported to be τ = 148 μs at room temperature.62 It is clear that the directly bound nature of the pyrene chromophore in 16 enhances the triplet reservoir effect. Complexes 13 and 14 were designed by Ward et al. with the intention of studying the intramolecular energy transfer processes between two chromophores with varying separation distance (complex 14 has an extended conformation where the distance between chromophores is as long as 21 Å).61 Excitation of the pyrene moiety results in efficient energy transfer to the 1MLCT state through a Förster type energy transfer mechanism (an antenna effect). Intersystem crossing to a 3MLCT state was observed, followed by equilibration between the 3MLCT and 3LC states resulting in a luminescence lifetime of τ ≈ 9 μs for both 13 and 14. The folding properties of the poly(ethylene glycol) linkage were found to influence the forward (kML) and reverse (kLM) triplet-triplet rates of the equilibrium such that through space energy transfer was allowed to proceed. The extension of the conjugated bridge between the phen ligand and the peripheral pyrene moiety via an acetylene linker in 15 results in the formation of an excited state that has a very long-lived excited state (τ = 58.4 μs). However, as reported by Zhao et al., this lifetime was attributed to the decay of a long-lived triplet intraligand and/or a ligand-to-ligand charge transfer (3IL/3LLCT) state.60 In this case, by bridging the two chromophores with an acetylene linkage, the energy of the ligand is lowered to a level where it may no longer equilibrate with the 3MLCT state (conversely, the use of a direct C-C covalent linkage results in the triplet reservoir effect, as shown for complex 16). 20  The last complex in Chart 1-5 (17), although not a derivative of [Ru(bpy)3] 2+ (1), was shown to exhibit a 3000-fold increase in emission lifetime (at room temperature) originating from the 3MLCT state versus an unsubstituted model complex, [Re(phen)(CO)3Cl] as a result of the 3MLCT equilibrating with a 3LC state localized on the peripheral naphthalene derived ligand (PNI). This lifetime (τ = 651 μs), is the longest excited state lifetime reported for Re(I)-based charge transfer photoluminescence (at room temperature).59 Through a combination of spectroscopic techniques, Castellano et al. were able to show that on excitation of the 1LC state, conversion to the 1MLCT state occurred efficiently and with a time constant of 45 ps. In less than 15 ns after intersystem crossing from the 1MLCT state to the 3MLCT state, equilibration or triplet energy transfer from the 3MLCT state to the 3LC state was observed. This impressive example fully illustrates the utility of these two-state equilibrations in the context of extending charge separated state lifetimes.  Figure 1-6. (left) Complex 18 and (right) a Jablonski diagram illustrating the relevant lowest lying states in complex 18 and their equilibria. Adapted from ref. 65  While equilibration of two states has been explored extensively, equilibration of three excited states is rare. McClenaghan et al. have reported the anthracene appended Cu+ complex 21  18 (Figure 1-6), where on irradiation; energy is stored in the appended organic moiety and transferred with high efficiency to the emission center via the equilibration of the three lowest lying excited states (a 1MLCT state, a 3MLCT state, and a 3LC state; Figure 1-6, right). Due to this equilibration, the excited state lifetime (τ = 1.2 μs) of this complex was found to be 15 times longer than that of the unsubstituted parent complex which incorporated no anthracyl moieties.65  Section 1.4 – Oligo- and polythiophenes  The discovery of metal-like conductivity in π-conjugated organic polymers has driven incorporation of these materials into electronic devices with a wide range of applications including organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs).66,67 The relative ease with which these materials may be synthetically varied, results in materials that are readily customized in order to elicit various desirable properties. Although many π-conjugated organic materials exist that may be used to enhance the optoelectronic properties of materials for photochemical energy conversion, to remain within the scope of this thesis, the discussion herein will be restricted to oligomeric (n = 2, 3, 4, etc.) and polymeric (n → ∞) forms of thiophene (Chart 1-6). Chart 1-6.  Organic π-conjugated materials consist of a sp2-hydridized carbon backbone, where the π system is expanded in the case of thiophene by the contribution of electrons from the heteroatom (i.e. the sulfur atom contributes two electrons).68 The electrons in this π system are delocalized 22  along the oligomer, or polymer chain due to the proximity of neighboring pz orbitals (the orbital housing the π system electron). As the chain length increases, the number of sulfur and sp2- hybridized carbon atoms increases, increasing the energy of the highest-energy occupied molecular orbital (HOMO) and decreasing the energy of the lowest occupied molecular orbital (LUMO).66 These energetic increases and decreases continue with each subsequent ring addition, increasing the number of valence π orbitals, until ultimately the electron structure of the system may be regarded as band-like (Figure 1-7). Within this electronic structure, the valence band is composed of occupied π orbitals, while the conduction band is composed of unoccupied π* orbitals. The separation between these bands is defined as the energy gap (Eg).   Figure 1-7. Simplified band diagram for oligo- and polythiophene. Shown are the expected changes between HOMO-LUMO levels on increasing the chain length. Adapted from ref. 66  Variations in the energy gap, Eg, and therefore the length of the oligomer or polymer of thiophene account for changes in the optoelectronic and conductivity properties of the material. For example, the bathochromic shift in absorption maximum observed between bithiophene (n = 23  2, λmax = 302 nm in CHCl3) 69 and sexithiophene (n = 6, λmax = 432 nm in CHCl3) 69 is a reflection of the narrowing of the energy gap between these two oligomer lengths. Geometric changes in the polymeric backbone, temperature and pressure changes, and electronic modifications within the backbone, may all also result in energy gap variations (ΔEg). 68 It is possible to polymerize thiophene or oligothiophene monomers to form polymers via electropolymerization, metal-catalyzed coupling reactions and chemical oxidative polymerization. Depending on the method of polymerization, the resulting products are amenable to different applications. Electrochemical polymerization involves applying an oxidative potential to a solution of monomer, to give a radical cation that combines rapidly with another radical, followed by elimination of 2H+.70 This process continues with the resulting monomeric, dimeric, trimeric, etc. species combining to form a polymer, and is advantageous due to the formation of the polymer film directly on an electrode surface.   Section 1.4.1 – Metal complexes bearing oligothiophenes  Due to their interesting and easily varied electronic and optoelectronic properties, oligothiophenes have been linked to metal centers for various applications. The metal center may influence the properties of the oligomer, and the properties of the oligomer may influence the metal center while also affording a synthetic pathway for the preparation of metal-containing polymers.71 Additionally, due to the electron-rich nature of these appended oligomers, electron transfer and energy transfer reactions between the metal and the oligomer are also possible. Some examples of complexes capitalizing on the properties of oligothienyl units are shown in Chart 1-7.   24  Chart 1-7. Ref. 72-77   Complexes 19-21 represent a relatively new class of complexes that have been created to be used as dyes in dye sensitized solar cells (DSSCs).8 These photoelectrochemical cells, although not strictly photosynthetic mimics, have become an attractive alternative for solar energy conversion due to the potential for low cost and relatively high efficiencies. The sensitizer dyes play a crucial role by first absorbing sunlight, then injecting a photoexcited electron into the conduction band of a semiconductor which then flows to an electrode to power a load. Most commonly, these dyes are based on Ru2+ polypyridyl complexes, and lead to power conversion efficiencies of 11% or more within these devices.78 Employing heteroatomic electron donating rings as end groups of the substituted bpy moiety (19-21) results in a destabilization of 25  the HOMO orbitals in these complexes. Nazeeruddin et al. have shown that on photoexcitation of 19 and subsequent electron injection into the semiconductor (TiO2) conduction band, the hole is partially localized on the substituted 3,4-ethylenedioxythiophene (EDOT) ligand, suggesting the EDOT ligand acts as an efficient donor moiety.74 Devices fabricated using 19 as the photosensitizers have power conversion efficiencies of 9.1%.  One important aspect in improving the efficiencies of DSSCs is the molar absorption coefficient of the photosensitizing dye. Ho and coworkers have shown that 20 has a higher absorption coefficient in high wavelength absorption bands (attributed to MLCT transitions from the Ru2+ center to the carboxylated bipyridine ligand) than previous DSSC dyes.75 These dyes were found to have a power conversion efficiency of 8.54%, a result of the photoexcited state residing on the carboxylated ligand (which acts as an anchor to the semiconductor surface) therefore lowering the distance the photoexcited electron has to travel to enter the circuit. Similarly, Ho et al. found that appending a bis(heptyl)carbazole moiety in 21 gives results comparable to those reported for 20 (a larger absorption coefficient and a high conversion efficiency of 8.98%).73 Dinuclear complex 22 is a hybrid adduct comprised of photoactive (the [Ru(bpy)3] 2+ termini) and electroactive (terthiophene bridge) components. Both subunits may absorb light, depending on the excitation wavelength, populating 1MLCT or 1LC (excitonic delocalization over the terthiophene core) levels that undergo intersystem crossing to their corresponding triplet states. CS states involving oxidation of the terthiophene bridge and reduction of the peripheral 2,2'-bipyridine ligands are also possible, however on examination of the thermally equilibrated energy levels, Ziessel et al. surmised that the typical 3MLCT emission expected from 26  [Ru(bpy)3] 2+ (1) is quenched by a low-lying 3LC state localized on terthiophene.76 These low- lying 3LC states may ultimately be used to conduct energies across oligothiophene based ‘wires.’  Complex 23 exhibits catalytic properties in asymmetric allylic alkylations (to give high enantioselectivities). Here, the sulfur containing rings of terthiophene have been shown to play a role in the stereodiscriminating catalytic step.77 Additionally, conductive films of 23 may be obtained through electropolymerization of the terthiophene moieties onto graphite electrodes.77 These films may be used as heterogeneous catalysts in the C-C bond forming Heck and Suzuki cross-coupling reactions,72,77 highlighting a new role for thiophene oligomers previously not discussed in this section. Metal complexes bearing oligomers of thiophene are interesting candidates for components in artificial photosynthesis. By tuning the electronic properties of the oligomer, the optoelectronic and excited state properties of the overall metal complex may be tailored in such a way as to afford an alignment of energy levels resulting in efficient formation of CS states or energy transfer.   Section 1.5 – Overview of transient absorption spectroscopy  In photosynthetic membranes, energy transfer processes take place on time scales of femtoseconds to picoseconds.9,79,80 The initial processes in the formation of 3MLCT states (1MLCT to 3MLCT intersystem crossing, for example) also take place on these same time scales (Section 1.2.1). Through the development of tunable fast and ultrafast laser systems, where high degrees of resolution are possible (sub 50 fs), real time studies of the aforementioned processes have become possible through transient absorption spectroscopy techniques.  27  In transient absorption spectroscopy, a small fraction of the molecules in a sample (0.1 to tens of percents depending on the experiment) are promoted to an electronically excited state by an excitation (or pump) pulse of a well-defined duration. Femtosecond pulses make it possible to study very fast energy and electron transfer processes (such as those in covalently linked systems) over a large spectral window with short temporal resolution, while slower processes such as bimolecular quenching, triplet absorption, or triplet to ground state singlet decay may be studied by nanosecond photolysis techniques, where the temporal window is much larger. After excitation, a probe pulse is passed through the sample with a time delay in relation to the pump pulse.81  This pump-probe sequence affords the possibility of calculating a difference spectrum (ΔA or ΔOD); the absorption spectrum of the excited sample minus the absorption spectrum of the sample in the ground state. Through the use of a streak camera (such as the one described in Section 2.2.2), it is possible to express the difference spectrum as a function of both time and wavelength offering insight into the dynamic processes occurring in the sample under study (electron migration, energy transfer, isomerization, photochemical reactions, etc.).82 One significant advantage of time-resolved absorption experiments over time-resolved fluorescence studies is the ability to probe and observe non-emissive or dark states. The difference spectrum is comprised of contributions from a number of different processes. Ground-state bleaching processes appear as a negative signal in the difference spectrum and arise from the decrease in the number of molecules in the ground state. In other words, the absorption of molecules in the ground state in the excited sample is less than that in the non-excited sample. Excited-state absorption features appear as a positive signal in the difference spectrum. These features are associated with optically allowed transitions from the 28  excited states of a chromophore to higher excited states, where certain probe wavelengths are absorbed.81  A significant possible contribution to the difference spectrum arises from photoproduct absorption. On excitation of a photochemical system, the formation of long-lived molecular states such as triplet states and CS states may occur. The absorptions arising from these transient products appear as positive signals in the difference spectrum with the exception of ground-state bleaching occurring at wavelengths at which the chromophore absorbs in the ground state.81 One important example of this type of contribution is the observation of the 2,2'-bipyridine anion (characterized through a positive absorption in the difference spectrum at short wavelengths) on excitation of [Ru(bpy)3] 2+ (1) to form the 3MLCT state (Section 4.3.3). This transient anion behaves as the gateway to many different photochemical reactions. If a photochemical reaction occurs in a system exhibiting photoproduct absorption (for example, the transfer of the electron giving rise to the aforementioned 2,2'-bipyridine anion to an electron acceptor), the excited state decays and the absorption attributed to the products of the reaction will appear (the absorption spectrum corresponding to the reduced electron acceptor, in the aforementioned scenario).  In general, the difference spectrum will be a sum of positive (for example, photoproduct absorption) and negative contributions (ground state bleaching). Whether there is a net bleach or a net absorption depends on the extinction coefficients for the species involved in the processes contributing to the difference spectrum. In the study of fast and ultrafast processes, such as those that may arise in photosynthetic and artificial photosynthetic systems, transient absorption spectroscopy lends invaluable insight into the nature of the excited state species.   29  Section 1.6 – Goals and scope  One strategy for improving the efficiency of artificial photosynthetic reaction centers is to take advantage of the equilibration of 3LC and 3MLCT states to extend the overall lifetime of the excited state. In addition, in a departure from the typical two-state model observed in systems exhibiting triplet reservoir effects, it may be possible to equilibrate a third state with intraligand charge transfer (ILCT) character with 3MLCT and 3LC states to extend the CS state lifetime by spatially separating the two charges formed on photoexcitation. Complexes bearing pendent oligothiophenes or ancillary ligands appended with oligothiophenes present an interesting target as photosynthetic reaction center mimics. This thesis deals primarily with the synthesis and spectroscopic characterization of Ru2+ complexes bearing thienyl appended ligands in order to determine the influence of the thienyl moieties on the excited state, and to determine the suitability of these ligand motifs in artificial photosynthesis and photochemical energy conversion. Chapter 2 introduces a series of new ligands based on the 1,10-phenanthroline diimine, where thienyl moieties (thienyl, bithienyl and terthienyl) are appended at the 5- position of the diimine via an amide linkage. The spectroscopic properties of these ligands are investigated, both as pro-ligands and also as ligands in a series of homoleptic and heteroleptic octahedral Ru2+ complexes, as well as cyclometalated Ir3+ complexes. The influence of these ligands on the excited state is quantified via a combination of ground state and excited state spectroscopic techniques, with a particular focus on excited state processes as observed by nanosecond transient absorption spectroscopy. Chapter 3 deals with the incorporation of these ligands into heteroleptic Ru2+ complexes bearing large planar polypyridyl acceptor ligands to form D-C-A triads that exhibit long-lived charge separated states, fueled by 30  3LC states localized on the thienyl moieties as well as the formation of two possible ILCT states within the acceptor ligands. Chapter 4 addresses a secondary aspect of this thesis. Based on the interesting photophysical properties reported in Chapters 2 and 3, Chapter 4 seeks to elucidate the role (if any) of the amide linkage in the formation of the overall excited states reported in the preceding chapters. A series of new 2,2'-bipyridine ligands bearing thienyl moieties appended either directly to the diimine or through an amide linkage are reported, as well as their analogous homoleptic and heteroleptic 2,2'-bipyridine Ru2+ complexes. A correlation between the structure of these complexes (via crystallographic data) and their photophysical properties (particularly their excited state behavior) is discussed.    31  CHAPTER 2  Ligand-triplet-fueled, long-lived, charge separation in Ru(II) complexes with bithienyl-functionalized ligands  Section 2.1 – Introduction  The need for new methods of efficiently converting solar energy to useable chemical energy was introduced in Chapter 1 (Section 1.1). Approaches that mimic photosynthesis rely on achieving long-lived charge-separated (CS) states via multistep, vectorial photoinduced electron transfer (Section 1.2.2).6,18 The utility of Ru2+ complexes with polypyridyl ligands as the backbone for functional molecular assemblies in artificial photosynthesis is discussed in Section 1.3. Metal-to-ligand charge transfer (MLCT) states in these complexes may act as the gateway to interligand charge transfer (ILCT) states that further separate the electron-hole pair.83  Covalently linking donor and/or acceptor moieties to metal-polypyridyl chromophores to give dyads or triads results in the formation of ILCT states (Section 1.2.2); however, the excited state lifetimes have generally been limited to ca. 1 μs and the energy stored (ΔGo) is <1.5 eV.38,84-86 Combined, these factors limit the utility of these systems in artificial photosynthesis.  In Chapter 3, some metal-polypyridyl triads that store a relatively high amount of energy and that are engineered with long-lived excited states are discussed. In this chapter, the preparation and photophysical characteristics of the ancillary or peripheral ligands that make these long-lived states possible is outlined, as well as their role in influencing the excited state properties of a series of homoleptic complexes. The excited state manifolds of metal polypyridyl complexes can include ligand centered (LC) states that are capable of acting as an intramolecular energy reservoir for MLCT states 32  (Section 1.3).61,64,87,88 This requires MLCT and LC states to lie close in energy in order to permit “fueling” of the MLCT state by the long-lived LC state. The work in this chapter introduces a system where a long-lived ligand-localized triplet acts as an energy reservoir to fuel population of an ILCT state with an unusually long lifetime (τ ≈ 7 μs) and a large amount of stored energy (ΔGo ≈ 2.0 eV), via an intermediate MLCT state. Chart 2-1. Ref. 89-91  One approach to generate these states is to introduce conjugated oligothiophenes, as ligands into Ru polypyridyl complexes (Chart 2-1) as described in Section 1.4.1.89-91  The possible role of the oligothiophene is two-fold.  First, the oligothiophene may reductively quench the Ru3+ species initially formed on photoexcitation, resulting in a CS state where a hole (h+) is localized on the oligothiophene.92  Secondly, reversible energy transfer from low-lying LC states on the conjugated ligand results in an extension of the excited state lifetime.56  The conjugated oligomers may also provide a route to preparing thin films of these complexes by electropolymerization,90,93 allowing the possibility of using these types of complexes in photovoltaic devices.     33  Chart 2-2.   The complexes reported in this chapter are Ru2+ polypyridyl complexes 31-34, and cyclometalated Ir3+ complexes 42-44 that incorporate the thienyl, bithienyl and terthienyl functionalized diimines (27-29) as ligands (Chart 2-2 and Chart 2-3, one possible isomer for each complex shown).  Through a series of spectroscopic investigations, it is illustrated that increasing the number of thienyl moieties in the ligand (cf. 27 and 29) and varying the number of conjugated ligands (cf. 32 and 33) sheds light on the photophysical properties of these complexes.    34  Section 2.2 – Experimental  Section 2.2.1 – General  Thiophene, n-BuLi (1.6 M in hexanes) and tetrathiafulvalene were all purchased and used as received from Aldrich. 1,10-Phenanthroline, nitrosonium hexafluorophosphate and ammonium hexafluorophosphate were used as received from Alfa Aesar. Methyl viologen dichloride (Sigma), RuCl3·xH2O (Strem), and SOCl2 (Fluka) were all also purchased from commercial sources, and used as received. All other solvents and reagents including those for NMR analysis (Cambridge Isotope Laboratories and Sigma) were obtained from commercial sources and used as received except where noted. 2,2'-Bithiophene and 2,2':5',2''-terthiophene were prepared according to literature procedure.94 Thiophene-2-carboxylic acid (35), [2,2'-bithiophene]-5-carboxylic acid (36), and [2,2':5',2''-terthiophene]-5-carboxylic acid (37) were all prepared according to a modified literature procedure; lithiation of the target oligothiophene with 1 eq. of n-BuLi followed by quenching with CO2(s) afforded the desired mono-acid. 95 Ru(DMSO)4Cl2, 96,97 [Ru(phen)3][PF6]2 (30)98 and Ru(phen)2Cl2 99 were also prepared as previously reported. 5-Amino-1,10- phenanthroline (38) was prepared using a combination of literature procedures (Scheme 2- 1).100,101 Synthesis of heteroleptic Ir3+ cyclometalated complexes (42-44) bearing phen, phen-tL (27) and phen-btL (28) ligands described in Section 2.3.5 was performed by Ashlee Howarth (University of British Columbia), via microwave synthetic techniques. These complexes were purified by silica column chromatography, in the same manner as the Ru2+ complexes reported below. 35   1H NMR spectra were recorded on either a Bruker AV300 (300 MHz) or Bruker AV400- Indirect (400 MHz) spectrometer, and 13C NMR spectra were collected on a Bruker AV600 (600 MHz) spectrometer. All chemical shifts are referenced to residual solvent signals which were previously referenced to tetramethylsilane.  Splitting patterns are designated as s (singlet), d (doublet), t (triplet), m (multiplet). EI-MS (Kratos MS-50), ESI-MS (Bruker Esquire), MALDI- TOF MS (Bruker Biflex IV), and elemental analysis were acquired at the UBC Microanalysis facility. Scanning electron micrographs were obtained on a Hitachi S-4700 Field Emission Scanning Electron Microscope (FESEM) at the UBC Bioimaging Facility. Samples for spectroscopic measurements were prepared using HPLC-grade Fisher solvents. Electronic absorption spectra were recorded on a Varian-Cary 5000 UV-Vis-near-IR spectrophotometer.  Emission spectra and quantum yield measurements were recorded on a Photon Technology International QuantaMaster 50 fluorimeter fitted with an integrating sphere, double monochromator and utilizing a 75W Xe arc lamp as the source.  Electropolymerization experiments were performed on a Pine Instruments bipotentiostat (AFCBP1) controlled with Aftermath software. Films were grown on pre-cut indium tin oxide (ITO) working electrodes that had been previously sonicated in soap and water, distilled water, and acetone and dried in an oven for an extended period of time. Pt mesh was used as a counter- electrode, and Ag wire was used as a pseudo-reference electrode. Experiments were carried out in anhydrous CH3CN (Sigma-Aldrich), with 0.1 M n-[Bu4N]PF6 as supporting electrolyte (recrystallized from EtOH three times, and left to dry under vacuum with heating).  Electrochemical data were obtained on a CHI620C electrochemical analyzer (CH Instruments, Austin, TX, USA). A single-compartment, three-electrode electrochemical cell was used with either a glassy carbon (1.5 mm diameter disk) or platinum (1.0 mm diameter disk) 36  from Cypress Systems as working electrode.  Immediately before use, the electrode was polished to a mirror finish with wet alumina (Buehler, 0.05 m), followed by rinsing with Millipore Milli- Q water and sonication. A Pt wire and a non-leak Ag/AgCl, satd KCl reference electrode (Cypress Systems, model EE009) were used as counter and reference electrodes, respectively.  All potentials were measured and are quoted vs. Ag|AgCl|satd. KCl reference electrode. All electrochemical data were recorded in acetonitrile with 0.1 M Bu4NPF6 as supporting electrolyte. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the electrochemical characterization of respective complexes. Transmittance spectroelectrochemical measurements were performed at constant potential in a quartz thin-layer compartment containing a platinum minigrid as working electrode. The liquid thin layer was spectroscopically probed as a function of time by using a diode array spectrometer (Hewlett-Packard model 8453).  The counter electrode (platinum wire) and the Ag/AgCl reference electrode were placed in the quartz cuvette near to the thin layer compartment.   Section 2.2.2 – Methods for collecting emission lifetime and transient absorption data  Emission lifetime data were collected using a Horiba Yvon Fluorocube TCSPC apparatus. In most cases, a 453 nm NanoLED source pulsing at a repetition rate of 50 – 100 kHz was used for excitation. Broadband emission was monitored by a CCD detector at wavelengths > 450 nm using a low pass filter.  All samples for luminescence studies were prepared in air and then purged with Ar for 15 – 30 minutes. All measurements were recorded at room temperature (21.0°C in the case of the emission and excited state lifetime measurements). Sample solutions were maintained under a blanket of Ar for the duration of the measurements in 1 cm2 quartz cells (NSG PCI cells) fitted with a rubber septum. 37  Transient absorption experiments were performed using an EKSPLA PL2241 mode-locked Nd:YAG laser that generated pulses of 35 ps (fwhm) in duration. The third harmonic output (355 nm) was used as the pump beam; the 1064 nm output beam pumped a Xe-filled quartz cell to generate the white light continuum used as the probe beam for measurements in the sub-200 ns time regimes. In longer time regimes, a Hamamatsu Xe lamp (E7536) was used. Where excitation wavelengths other than 355 nm were required, an EKSPLA Model PG401 Picosecond Optical Parametric Generator was pumped at 355 nm by a PL2241 mode-locked laser to produce wavelengths from 420 – 680 nm (Signal) and 720 – 2300 nm (Idler). The pump and probe beams were aligned to pass through the sample at a 90° angle and focused so that the probe beam was completely enclosed by the pump beam. The probe beam was detected by passage through a monochromator (Princeton Instruments SpectraPro 2300i) equipped with a 150 g/mm – 300 g/mm grating. The grating was typically centered at 540 nm in order to collect data over the 370- 730 nm spectra range. This monochromator was coupled to a streak camera (Hamamatsu C7700) and a CCD detector (Hamamatsu C8484) digitizing the images from the streakscope. The trigger delay between the streak camera and pulse firing was controlled using a passive delay unit (Hamamatsu C1097-01). Computer control of data acquisition was through the HPD-TA software (ver. 8.3) from Hamamatsu. The data mostly consists of 100-shot averages. Samples were prepared for transient absorption in air, in HPLC-grade solvents (Fisher) and purged with Ar for 30 minutes. In all cases, steady-state UV-Vis absorption spectra collected before and after laser photolysis confirmed no sample degradation. Samples were prepared such that the absorbance of the solution at the excitation wavelength was 0.8 – 1 A.U.  In order to determine excited state and emission lifetimes, decay curves obtained from fluorescence lifetime and transient absorption measurements were fit using both 38  monoexponential and biexponential models (via the DAS6 Data Analysis software package, or OriginPro).  The fit producing a χ2 value closest to unity was used in determining the reported lifetime.  In most instances (except where noted), a monoexponential model was found to be the best fit.  In all cases, the reported lifetimes and time resolved spectra were found to be reproducible over multiple trials: one representative lifetime or spectrum from this series of trials is reported in each case.   Section 2.2.3 – Methods  N-(1,10-phenanthrolin-5-yl)-thiophene-2-carboxamide (27, phen-tL) SOCl2 (5 mmol, 0.5 ml) and DMF (2 drops) were added to a suspension of thiophene-2- carboxylic acid 35 (2.00 mmol, 256 mg) in 5 ml of CH2Cl2. The reaction mixture was heated to reflux for 1 h. The mixture was then cooled to room temperature and the solvent was removed under reduced pressure to yield a yellow oily residue. This residue, the acyl chloride of thiophene-2-carboxylic acid (35Cl) was used without purification in the next step.  The flask containing the acyl chloride was cooled to 0°C and placed under N2. To this residue a solution of 5-amino-1,10-phenanthroline 38 (0.800 mmol, 156 mg) and TEA (0.1 ml) in 15 ml of CHCl3 was added dropwise. A significant amount of gas evolved and was released. After addition, the reaction mixture was left to warm to room temperature, and then heated to reflux for 19 h under N2. The crude product precipitated as a yellowish-orange fine solid at the end of the heating period, was isolated by filtration and recrystallized from EtOH-H2O. Yield: 0.08 g (33%). 1H NMR (400 MHz, MeOD) δ ppm 7.32 (dd, J = 5.03, 3.81 Hz, 1 H) 7.88 (dd, J = 5.18, 1.22 Hz, 1 H) 8.14 (dd, J = 3.81, 1.07 Hz, 1 H) 8.18 (dd, J = 8.53, 4.87 Hz, 1 H) 8.24 (dd, J = 8.22, 5.18 Hz, 1 H) 8.48 (s, 1 H) 8.99 (dd, J = 8.53, 1.52 Hz, 1 H) 9.09 (dd, J = 8.22, 1.22 Hz, 1 H) 9.25 (dd, J 39  = 5.18, 1.52 Hz, 1 H) 9.32 (dd, J = 4.72, 1.37 Hz, 1 H). 13C NMR (150.92 MHz, DMSO-d6) δ ppm 123.08 (2xCH), 123.66, 125.76, 127.93, 128.30, 129.74, 131.57, 132.23, 132.37, 136.07, 139.18, 144.34, 145.86, 149.84, 150.04, 161.14. HR-EI MS m/z: calcd for C17H11N3OS, 305.06228; found, 305.06243 (-0.5 ppm).  N-(1,10-phenanthrolin-5-yl)-2,2´-bithiophene-5-carboxamide (28, phen-btL) The title compound was prepared using the same method as described for phen-tL (27). CHCl3 was used in the preparation of the acyl chloride, and was purged with N2 (15 minutes) prior to the addition of [2,2´-bithiophene]-5-carboxylic acid (36). The final product was used without purification. Yield: 0.162 g (84%). 1H NMR (300 MHz, MeOD) δ ppm 7.13 (dd, J = 5.12, 3.58 Hz, 1 H) 7.40 (d, J = 4.10 Hz, 1 H) 7.44 (d, J = 3.84 Hz, 1 H) 7.50 (d, J = 5.12 Hz, 1 H) 8.05 (d, J = 4.10 Hz, 2 H) 8.22 (ddd, J = 18.11, 8.38, 4.99 Hz, 2 H) 8.49 (s, 1 H) 9.01 (dd, J = 8.58, 1.41 Hz, 1 H) 9.10 (dd, J = 8.19, 1.28 Hz, 1 H) 9.24 (dd, J = 5.12, 1.28 Hz, 1 H) 9.32 (dd, J = 4.74, 1.41 Hz, 1 H). 13C NMR (150.92 MHz, MeOD) δ ppm 122.02 (2×CH), 124.72, 125.07, 125.50, 125.86, 126.46, 127.26, 128.74, 129.22, 131.63, 133.13, 135.58, 136.69, 136.81, 141.89, 142.39, 145.80, 146.65, 149.03, 160.86. HR-EI MS m/z: calcd for C21H14N3OS2, 388.0578; found, 388.0575 (-0.9 ppm).  N-(1,10-phenanthrolin-5-yl)-[2,2':5',2''-terthiophene]-5-carboxamide (29, phen-ttL) The title compound was prepared using the same method as described for phen-tL (27). CHCl3 was used in the preparation of the acyl chloride, and was thoroughly purged with N2 prior to the addition of [2,2':5',2''-terthiophene]-5-carboxylic acid (37). The final product was used without purification. Yield: 0.050 mg (63%). 1H NMR (400 MHz, DMSO-d6) δ ppm 7.10 - 7.16 40  (m, 1 H) 7.34 (d, J=3.75 Hz, 1 H) 7.40 (d, J=3.07 Hz, 1 H) 7.49 (d, J=3.75 Hz, 1 H) 7.53 (d, J=3.75 Hz, 1 H) 7.57 (d, J=5.12 Hz, 1 H) 8.15 - 8.24 (m, 2 H) 8.26 - 8.31 (m, 1 H) 8.48 (s, 1 H) 8.99 (d, J=8.19 Hz, 1 H) 9.10 (d, J=7.85 Hz, 1 H) 9.24 (d, J=4.44 Hz, 1 H) 9.32 (d, J=3.41 Hz, 1 H) 11.17 (br. s., 1 H). ESI MS m/z 470.1 ([M+H]+).  Ru(phen-tL)2Cl2 (40) Compound 27 (100 mg, 0.327 mmol, 2 eq) was dissolved in 10 ml of EtOH:H2O (4:1). A large excess of LiCl was added (6 mmol).  The mixture was warmed to dissolve phen-tL (27) and purged with N2 for 15 minutes prior to the addition of Ru(DMSO)2Cl2 (79.4 mg, 0.164 mmol).  The reaction mixture was heated to reflux overnight, and then concentrated under reduced pressure until a brown solid precipitated. This crude product was isolated by filtration, washed with an excess of EtOH and acetone, and dried under vacuum.  Due to poor solubility, this product was used in the next step without purification. Yield: 0.125 g (97%). MALDI-TOF MS m/z 749.8 ([M-Cl]+).  Ru(phen-btL)2Cl2 (41) Ru(phen-btL)2Cl2 was prepared using the same method as Ru(phen-tL)2Cl2 (40). After heating to reflux, a very dark purple solid was suspended in the reaction mixture. This solid was isolated by filtration, washed with EtOH and acetone, dried under vacuum and used in the next step without further purification. Yield: 0.177 g (68%). MALDI-TOF MS m/z 911.2 ([M-Cl]+).   41  [Ru(phen-tL)3][PF6]2 (31) Complex 40 (80 mg, 0.10 mmol) and 27 (46 mg, 0.15 mmol) were combined in 10 ml of a EtOH:H2O (4:1) mixture that had been purged with N2 for 15 minutes. The reaction mixture was heated to reflux overnight, cooled to room temperature and the desired product was precipitated as an orange-brown solid through the addition of a saturated solution of NH4PF6(aq). To purify the product, it was first dissolved in CH3CN and then passed through a silica column using a CH3CN:H2O:KNO3(aq) (96:3:1) eluent. The major orange band was collected, concentrated under reduced pressure and converted to the hexafluorophosphate salt by addition of a saturated NH4PF6(aq) solution.  The resulting bright orange product was collected by vacuum filtration, washed with NH4PF6(aq) and water, and then dried under vacuum to give the title compound. Yield: 0.015 g (12 %).  1H NMR (400 MHz, CD3CN) δ ppm 7.28 - 7.33 (m, 5 H) 7.67 (dddd, J=10.85, 8.19, 5.48, 2.59 Hz, 10 H) 7.82 (d, J=4.87 Hz, 4 H) 8.03 (d, J=3.96 Hz, 7 H) 8.04 - 8.07 (m, 3 H) 8.10 - 8.15 (m, 5 H) 8.51 (d, J=1.83 Hz, 5 H) 8.60 (d, J=8.22 Hz, 5 H) 8.72 (d, J=8.53 Hz, 5 H) 9.31 (s, 5 H). 13C NMR (150.92 MHz, CD3CN) δ ppm 121.71 (2xCH), 124.86, 125.65, 127.34, 127.92, 129.45, 130.09, 132.04, 132.87, 133.24, 136.00, 145.92, 147.82, 152.11, 152.88, 161.01. HR-ESI MS m/z: ([M-PF6] +) calcd for C51H33N9O3F6PS3Ru, 1159.0540; found, 1159.070 (-2.6 ppm).  [Ru(phen-btL)3][PF6]2 (32) The title complex was prepared and purified using the same method as for [Ru(phen- tL)3][PF6]2 (31).  Yield: 0.030 g (18 %).  1H NMR (400 MHz, CD3CN) δ ppm 7.14 (dd, J=5.03, 3.81 Hz, 1 H) 7.39 (d, J=3.96 Hz, 1 H) 7.44 (d, J=3.65 Hz, 1 H) 7.48 (d, J=5.18 Hz, 1 H) 7.66 (dddd, J=13.52, 8.26, 5.33, 2.74 Hz, 2 H) 7.93 (d, J=3.96 Hz, 1 H) 8.00 - 8.06 (m, 1 H) 8.09 - 42  8.15 (m, 1 H) 8.50 (d, J=2.44 Hz, 1 H) 8.58 (d, J=8.53 Hz, 1 H) 8.72 (d, J=8.53 Hz, 1 H) 9.31 (s, 1 H). 13C NMR (150.92 MHz, CD3CN) δ ppm 121.76, 124.05, 124.91, 125.32, 125.67, 126.47, 127.32, 128.11, 130.06, 130.41, 132.89, 133.19, 135.40, 136.00, 136.17, 142.95, 145.89, 147.82, 152.04, 152.87, 160.76. ESI MS m/z 1408.2 ([M-PF6] +). Anal. Calcd. for C63H41F12N9O4P2RuS6 (32 + H2O): C, 48.15; H, 2.63; N, 8.02. Found: C, 48.11; H, 2.80; N, 7.82.  [Ru(phen)2(phen-btL)][PF6]2 (33) Ru(phen)2Cl2 (69 mg, 0.13 mmol) and 28 (50 mg, 0.13 mmol) were suspended in a mixture of 4:1 EtOH:H2O that had been purged with N2 for 15 minutes. The reaction mixture was left to reflux under N2 overnight, then cooled to room temperature and filtered through glass wool to remove any insoluble impurities. The filtrate was added to a stirring saturated aqueous solution of NH4PF6 and the resulting orange-red precipitate was collected. The product was purified using column chromatography as in the synthesis of [Ru(phen-tL)3][PF6]2 (31). Yield: 0.040 g (27%). 1H NMR (600 MHz, CD3CN) δ ppm 7.13 (dd, J=5.12, 3.58 Hz, 1 H) 7.38 (d, J=4.10 Hz, 1 H) 7.44 (d, J=3.58 Hz, 1 H) 7.48 (dd, J=5.12, 1.02 Hz, 1 H) 7.58 - 7.68 (m, 4 H) 7.93 (d, J=4.10 Hz, 1 H) 7.97 - 7.99 (m, 1 H) 8.00 - 8.03 (m, 1 H) 8.05 - 8.09 (m, 2 H) 8.25 (s, 2 H) 8.48 (s, 1 H) 8.56 (d, J=7.68 Hz, 1 H) 8.60 (t, J=8.70 Hz, 2 H) 8.69 (d, J=7.68 Hz, 1 H) 9.35 (s, 1 H). 13C NMR (150.92 MHz, CD3CN) δ ppm 123.46, 125.85, 126.58, 127.11, 127.22, 127.36, 128.27, 129.06, 129.36, 129.39, 129.90, 131.83, 132.12, 132.33, 132.36, 134.56, 134.95, 137.70, 138.11, 138.15, 144.74, 147.70, 149.22, 149.27, 149.65, 153.80, 154.25, 154.28, 154.36, 154.39, 154.60, 162.50. ESI MS m/z 994.2 ([M-PF6] +). Anal. Calcd. for C45H31F12N7O2P2RuS2 (33  + H2O): C, 46.72; H, 2.70; N, 8.47. Found: C, 46.78; H, 2.83; N, 8.42.  43  [Ru(phen)2(phen-ttL)][PF6]2 (34) The title complex was prepared using the same method as [Ru(phen)2(phen-btL)][PF6]2 (33). This complex was prepared on a very small scale, and the entirety of the product was used in the 1H NMR measurement, and the subsequent spectroscopic measurements. No yield was recorded. 1H NMR (400 MHz, CD3CN) δ ppm 7.10 (dd, J=5.03, 3.50 Hz, 1 H) 7.26 (d, J=3.65 Hz, 1 H) 7.33 (dd, J=3.50, 1.07 Hz, 1 H) 7.36 - 7.43 (m, 3 H) 7.57 - 7.69 (m, 6 H) 7.94 (d, J=4.26 Hz, 1 H) 7.96 - 8.04 (m, 3 H) 8.05 - 8.10 (m, 3 H) 8.25 (s, 4 H) 8.49 (s, 1 H) 8.54 - 8.64 (m, 5 H) 8.70 (d, J=8.53 Hz, 1 H) 9.36 (s, 1 H).  Section 2.3 – Results and discussion  Section 2.3.1 – Synthesis and characterization  Ligands phen-tL (27), phen-btL (28), and phen-ttL (29) were all prepared using a stepwise procedure (Scheme 2-1). The target thienyl carboxylic acid (35-37) was treated with SOCl2 in CH2Cl2 or CHCl3 in the presence of catalytic amounts of DMF, giving the acyl chloride derivative (35Cl-37Cl). The acyl chloride was cooled to 0°C and used immediately in the next step; a solution of 5-amino-1,10-phenanthroline (38) in CHCl3 with TEA was slowly added to the acyl chloride residue under positive nitrogen flow. The mixture was warmed to room temperature, and then heated to reflux overnight resulting in formation of off-white (27) to light orange (29) precipitates, which in all cases were found to be the desired ligand. The expected structures of the ligands were confirmed through NMR spectroscopy, and high resolution mass spectrometry.  The electronic character of these ligands was elucidated using various ground state and excited state spectroscopic methods. The precipitates isolated from the synthetic procedure were found to be of satisfactory purity for use in the preparation of the Ru2+ 44  complexes discussed in this chapter. Of all three ligands, only phen-tL (27) was further purified through recrystallization, due to the insolubility of phen-btL (28) and phen-ttL (29).  Scheme 2-1.  The amino precursor, 5-amino-1,10-phenanthroline (38) was prepared in two steps (Scheme 2-2); nitration of 1,10-phenanthroline with H2SO4/fuming HNO3 gave 5-nitro-1,10- phenanthroline (39). Reduction of 5-nitro-1,10-phenanthroline (39) with 10% Pd/C and N2H4 in EtOH gave 5-amino-1,10-phenanthroline (38) as previously reported in literature.100,101 Scheme 2-2.  Homoleptic metal complexes [Ru(phen-tL)3][PF6]2 (31) and [Ru(phen-btL)3][PF6]2 (32) were prepared by reacting phen-tL (27) or phen-btL (28) with Ru(DMSO)4Cl2 (Scheme 2-3) while [Ru(phen)2(phen-btL)][PF6]2 (33) was prepared through reaction of phen-btL (28) with 45  Ru(phen)2Cl2.  The asymmetrical substitution of the phen ligand can result in several possible isomers of these complexes; however 1H NMR spectroscopy of the homoleptic complexes showed no appreciable signal broadening, suggesting either only one isomer is formed or any isomers present are not sufficiently different to result in chemical shift differences. The 1H NMR spectra are consistent with symmetrical species, confirming the expected D3 geometry of the homoleptic complexes, and the C2 geometry of the heteroleptic complex. Scheme 2-3.   Section 2.3.2 – Photophysical properties  The ground state absorption spectra of ligands 27-29 (Figure 2-1) exhibit two distinct features. A higher energy feature (λmax = 268 nm, in 27; λmax = 284 in 28 and 29) attributed to transitions localized on the phen portion of the ligand, and a lower energy feature that appears as a shoulder in 27 (λmax = 306 nm) and shifts to progressively longer wavelengths in 28 (λmax = 344 nm) and 29 (λmax = 378). This lower energy feature is attributed to π  π* transitions localized on the oligothienyl portion of the ligand, and the shift to lower energy maxima correlates to an 46  increase in conjugation in this portion of the ligand and a subsequent narrowing of the band gap.102   Figure 2-1. Normalized absorption spectra of ligands 27-29 (CH3CN).   The absorption spectrum of [Ru(phen-tL)3][PF6]2 (31, Figure 2-2) exhibits moderately intense Ru dπ  π* MLCT bands (λmax = 450 nm with a shoulder at λmax = 420 nm), and LC bands in the UV region.  These spectral features are comparable to those observed for [Ru(bpy)3] 2+ (1) and [Ru(phen)3][PF6]2 (30) (Figure A1-1). 25,26  Complexes [Ru(phen- btL)3][PF6]2 (31) and [Ru(phen)2(phen-btL)][PF6]2 (33) exhibit similar spectra with an additional intense band at λmax = 355 nm attributed to a bithienyl π  π* transition of the ligand.  The band at 355 nm is more intense in [Ru(phen-btL)3][PF6]2 (31) than in [Ru(phen)2(phen-btL)][PF6]2 (33), as expected due to the number of bithienyl chromophores present. Furthermore, no 47  significant ground-state electronic interaction between the Ru2+ core and the thienyl moieties is evident from these spectra.   Figure 2-2. Absorption and emission spectra of complexes 31-33 (CH3CN, λex = 450 nm).  Excitation into the lowest energy absorption band of 31-33 results in identical emission spectra centered at 596 nm (Figure 2-2), similar to that observed for  [Ru(phen)3][PF6]2 (30).  Emission quantum yields for 31-33 (Table 2-1) are comparable to that previously reported for [Ru(bpy)3] 2+ (Φem = 0.095). 103  Interestingly, the emission lifetimes, τem (λex = 453 nm), at room temperature are significantly different for the three complexes; varying from 0.89 μs for [Ru(phen-tL)3][PF6]2 (31) to 7.4 μs for [Ru(phen-btL)3][PF6]2 (32). By comparison, [Ru(phen)3][PF6]2 (30) has an emission lifetime of 523 ns under identical conditions.  48  Table 2-1. Select photophysical properties of ligands and complexes presented in this chapter Compound λem / nm a Φem b,c τem c,d τes (λ / nm) c,e phen-tL (27) 308    phen-btL (28) 405   > 10 μs [Ru(phen)3][PF6]2 (30) 600 f 0.036g 523 ns 534 ns [Ru(phen-tL)3][PF6]2 (31) 596 f 0.047 ± 0.005 891 ns 973 ns (450) [Ru(phen-btL)3][PF6]2 (32) 596 f 0.071 ± 0.001 7.4 μs 5.9 μs (395 – 426), 6.2 μs (420 – 450), 6.2 μs (460 – 490), 6.3 μs (520 – 560) [Ru(phen)2(phen-btL)][PF6]2 (33) 596f 0.058 ± 0.001 2.9 μs 2.5 μs (395 – 450), 2.6 μs (460 – 620) aUncorrected, room temperature, CH3CN solution. bAbsolute quantum yield at room temperature. cSamples prepared in air and purged with Ar for 30 min. dλex = 453 nm. eλex = 355 (fwhm = 35 ps). fλex = 450 nm. gCalculated by comparison to [Ru(bpy)3] 2+ (1)104   Figure 2-3. Excited state difference spectra of [Ru(phen-tL)3][PF6]2 (31, black), [Ru(phen- btL)3][PF6]2 (32, teal), [Ru(phen)2(phen-btL)][PF6]2 (33, blue) and [Ru(phen)3][PF6]2 (30, red); t = 65 – 265 ns (CH3CN, λex = 355 nm, fwhm = 35 ps).   49   Figure 2-4. Excited state difference spectra of [Ru(phen-tL)3][PF6]2 (31, black) and [Ru(phen- btL)3][PF6]2 (32, red); t = 5-6 ns (CH3CN, λex = 355 nm, fwhm = 35 ps).  Figure 2-3 depicts time-resolved transient absorption (TA) difference spectra of 30-33.  Complex [Ru(phen-tL)3][PF6]2 (31) shows a strong ground state MLCT bleach between 400-500 nm and absorptions at 356 and 550 nm attributed to transitions localized on a phen anion.24,105 These spectral features closely resemble those observed for [Ru(phen)3][PF6]2 (30). The bathochromic shift observed in the high energy band (λmax = 356 nm) of [Ru(phen-tL)3][PF6]2 (31) is attributed to some charge delocalization over the amide bond, or as discussed in Chapter 4 a narrowing of the HOMO-LUMO gap due to the electron donating character of the amide linkage.  Simultaneous decay of the TA bands of [Ru(phen-tL)3][PF6]2 (31) was fit to a single exponential model with τes = 973 ns (Figure A1-2).  The similarity in emission and TA lifetimes for [Ru(phen-tL)3][PF6]2 (31, 891 ns vs. 973 ns),  and similarities to the TA and emission spectra for related species, strongly supports the assignment of the major excited state species in [Ru(phen-tL)3][PF6]2 (31) as a 3MLCT state.  Interestingly, the excited state lifetime is longer 50  than that of [Ru(phen)3][PF6]2 (30).  It is possible that a minor contribution from a 3LC state on the thienyl group results in the longer lifetime. In contrast to [Ru(phen-tL)3][PF6]2 (31), TA spectra of [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)3][PF6]2 (33) exhibit a broad, multi-featured absorption between 390-450 nm, a lower energy feature at 450-500 nm and a broad, low energy absorbance at 550 nm (Figure 2-3).  Qualitatively, the spectra of complexes [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen- btL)3][PF6]2 (33) are similar suggesting that the excited state species are the same.  At short time regimes (t < 100 ns) a ground state bleach is also observed at 340 nm, corresponding to the ground state bithienyl π  π* absorption (Figure 2-4).  The excited state lifetimes (Figure A1-3, A1-4) of the two bithienyl complexes are comparable to the emission lifetimes observed for these species.  The states observed in the TA spectra of [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)3][PF6]2 (33) are evidently quite different from the 3MLCT state observed for [Ru(phen-tL)3][PF6]2 (31) and [Ru(phen)3][PF6]2 (30).  Figure 2-5. A high resolution TA difference spectrum of complex 32 (CH3CN, t = 0 – 2 μs, λex = 355 nm, fwhm = 35 ps, grating = 150 g/mm).  51   Adjusting the grating on the TA instrument monochromator (transitioning from 300 grooves/mm to 150 grooves/mm) offers a high-resolution insight into the nature of the absorption bands found in the 400-500 nm region of the excited state spectrum of [Ru(phen- btL)3][PF6]2 (32). Here, it appears that this region of the excited state spectrum is actually composed of three separate bands, indicating that there may be multiple states taking part in forming the overall excited state manifold of this complex (Figure 2-5). It is well established that 3LC states can equilibrate with 3MLCT states of comparable energies.61,64,87 The triplet energy of unsubstituted bithiophene is 2.2 eV,102 close to the 3MLCT energy (2.08 eV) of [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)3][PF6]2 (33) calculated from the 3MLCT emission band, suggesting that equilibration of 3LC and 3MLCT states is possible.  The excited state absorption of phen-btL (28) at 400 nm (Figure 2-6) is coincident with the high energy band in the TA spectrum of [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)3][PF6]2 (33), thus it is likely that a non-emissive 3LC state is present in the complexes and is responsible, in part, for the long lifetime of the excited state. This is further evidenced by the approximately threefold decrease in lifetime between [Ru(phen)2(phen- btL)3][PF6]2 (33) and [Ru(phen-btL)3][PF6]2 (32), where [Ru(phen)2(phen-btL)3][PF6]2 (33) has only a third of the bithienyl substituents of [Ru(phen-btL)3][PF6]2 (32) and thus a smaller ‘triplet reservoir’, an effect previously observed in Ru2+-pyrenyl complexes.62 Additionally, the same spectral features are observed in the TA spectrum of [Ru(phen-btL)3][PF6]2 (32) when an excitation wavelength of 450 nm is used (Figure A1-5), suggesting that the same excited state is formed regardless of excitation pathway. 52   Figure 2-6. Normalized TA difference spectra for [Ru(phen-btL)3][PF6]2 (32) and phen-btL (28). (CH3CN, λex = 355 nm, fwhm = 35 ps)  It is evident, however, that an additional excited state species must be present in [Ru(phen- btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)][PF6]2 (33) since there are two additional bands in the TA spectra of these complexes that are absent in the TA spectrum of phen-btL (28), centered at 475 and 550 nm.  It is possible that a charge-separated 3ILCT state can also equilibrate with the 3MLCT state, in addition to the 3LC state.  This 3ILCT state would form by reductive quenching of Ru3+ by the bithienyl group giving rise to a 3ILCT state consisting of a bithienyl cation and an anion localized either on the phen group or possibly delocalized to the amide. This possibility was investigated through spectroelectrochemistry of [Ru(phen-btL)3][PF6]2 (32).   Differential pulse voltammetry (DPV) of [Ru(phen-btL)3][PF6]2 (32) showed a shoulder at 1.25 V and two waves at 1.38 V and 1.50 V vs. Ag/AgCl (first positive-going potential scan, Figure A1-6).  These two waves are assigned to oxidation of the Ru2+ center and the oxidation of the bithienyl moieties, respectively.  It is apparent that oxidative polymerization of the bithienyl 53  groups is occurring as sequential scans show increasing amplitude and simultaneous formation of a yellow film on the electrode (Section 2.3.4).  The reductive DPV of [Ru(phen-btL)3][PF6]2 (32) shows a very broad cathodic process between -0.7 and -1.1 V followed by a more pronounced anodic peak at ca. -0.9 V, assigned to reduction of the substituted phen ligand.106  This wave is not observed in 30 (first reduction ca. -1.35 V, Figure A1-7). Despite the less negative reduction potential in [Ru(phen-btL)3][PF6]2 (32), no bathochromic shift is observed in the emission spectrum or the MLCT absorption of [Ru(phen-btL)3][PF6]2 (32) compared to [Ru(phen)3][PF6]2 (30).  This is attributed to the bichromophoric nature of [Ru(phen-btL)3][PF6]2 (32); here optical transitions and redox processes may be localized on separate orbitals.107 This is further evidenced by comparison with [Ru(phen-tL)3][PF6]2 (31), which has an identical first reduction potential (Figure A1-8), and emission (596 nm, 2.08 eV), but a red-shift in the band assigned to the phen anion in the excited state TA spectrum (with respect to the same band in 30).  At more negative potentials, further reduction waves are observed due to subsequent reduction of the phen groups.  Gibbs free energy changes for intramolecular electron transfer were calculated (Equation 1-1, 1- 2)108 to be ΔETG° ≈ -14 kJ/mol -1 (-0.14 eV) indicating that formation of an intramolecular ILCT state is energetically feasible.  The broadness and poor reversibility of the DPV peaks in [Ru(phen-btL)3][PF6]2 (32) makes a definitive assignment of the stored energy, ΔGo, of the ILCT state impossible. However, its value may be estimated as ≥ 1.9 eV. This compares to a calculated value of 2.0 eV in [Ru(phen-tL)3][PF6]2 (31) and reveals that it is energetically accessible. 54   Figure 2-7. Reductive spectroelectrochemistry of [Ru(phen-btL)3][PF6]2 (32, -0.85 V, 50 μM solution in CH3CN, black), and differential excited state spectrum of [Ru(phen-btL)3][PF6]2 (32, red) at t = 0 - 2 μs (CH3CN, λex = 355 nm, fwhm = 35 ps).  Reductive spectroelectrochemistry of [Ru(phen-btL)3][PF6]2 (32) shows three distinct spectral features: a strong absorbance at 390 nm, a shoulder at 428 nm and a low-energy band at 484 nm (Figure 2-7).  This differs substantially from the spectra obtained upon electroreduction of [Ru(phen)3][PF6]2 (30), where the MLCT band at 425 nm is bleached, while a broad absorption between 500-750 nm is observed due to formation of a phen anion bound to a Ru2+ center (Figure A1-9). As a result, the spectral features of [Ru(phen-btL)3][PF6]2 ▪- (32▪-) are assigned to a substituted phen anion bound to a Ru2+ center.  Comparison of the spectrum of [Ru(phen-btL)3][PF6]2 ▪-  (32▪-) with the TA spectrum of [Ru(phen-btL)3][PF6]2 (32) shows excellent overlap, suggesting that the excited state is similar to the Ru2+-phen▪- state observed in the spectroelectrochemistry (Figure 2-7).  55   Figure 2-8. Chemical oxidation of phen-btL (28) with increasing amounts of NOPF6 in CH3CN.  Oxidative spectroelectrochemistry of [Ru(phen-btL)3][PF6]2 (32) was not possible as this species electropolymerized (Section 2.3.4) under these conditions; however, chemical oxidation of phen-btL (28) with NOPF6 was carried out in dilute solution, and showed growth of a band between 375-440 nm (Figure 2-8) due to 28+.  Previously, the radical cation of bithiophene has been shown to absorb at 420 nm, with a weak low energy absorption at 580 nm.109-111  In the TA spectra of [Ru(phen-btL)3][PF6]2 (32), some of the high energy features between 390 and 450 nm, attributed to triplet bithiophene, may also correspond to an oxidized bithienyl moiety.   56   Figure 2-9. Differential absorption spectra of [Ru(phen-btL)3][PF6]2 (32) in the presence of TTF, illustrating decreases in absorption in the 400-450 nm region up to 2 μs after excitation (CH3CN, λex = 355 nm, fwhm = 35 ps).  Addition of a sacrificial electron donor, tetrathiafulvalene (TTF), to [Ru(phen-btL)3][PF6]2 (32) during the TA experiment results in bleaching of the high energy bands of 32, concomitant with the growth of bands corresponding to TTF+ (Figure 2-9).112  TTF donates an electron to the oxidized bithienyl moiety formed via reductive quenching of the photoexcited Ru3+.  Addition of an electron acceptor, methyl viologen (MV2+), yielded reversible electron transfer from photoexcited 32* to form MV▪+ as evidenced by growth of bands corresponding to reduced MV2+ in the UV-Vis and TA spectra (Figure 2-10).113  Importantly, bleaching in the 400–500 nm region also occurs, indicating the spectral features of both the oxidized and reduced species in the ILCT state overlap to a significant extent.  These data together support the formation of the charge separated ILCT species in [Ru(phen-btL)3][PF6]2 (32). 57   Figure 2-10. (a) TA spectra of [Ru(phen-btL)3][PF6]2 (32) in the presence of MV 2+, up to 2 μs after excitation. Pictured is the bleaching of the bands corresponding to the excited state 32 species concomitant with growth of  bands corresponding to the formation of MV▪+ at 400 nm and 600 nm.113 (λex = 355 nm) (b) Ground state absorption spectrum of 32 (CH3CN) in the presence of an excess of MV2+ before laser irradiation at 355 nm (black), and after irradiation (red). Bands at 400 nm, and 600 nm correspond to the reduced MV▪+ species.113  With all of these considerations in place, it is possible to envision three interacting excited states in [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen)2(phen-btL)][PF6]2 (33, Figure 2-11).  A long- lived bithienyl-localized 3LC state acts as a reservoir to populate both the 3MLCT state, which is the only species to decay radiatively, and a 3ILCT state in which the electron and hole are localized on the phenanthroline and bithienyl portions of the complex, respectively.  The emission at 596 nm for 32 and 33 along with the absence of any 3MLCT bands in the TA spectra suggests that both the 3LC and 3ILCT states are close to, but slightly lower in energy than the 3MLCT state. In this case, the triplet reservoir extends the lifetimes of both the 3MLCT and 3ILCT states.  (a) (b) 58   Figure 2-11. Jablonski diagram of [Ru(phen-btL)3][PF6]2 (32) in CH3CN.   Section 2.3.3 – Effect of longer conjugation length in ligands  To take advantage of the equilibration of 3LC states with a 3MLCT state in order to fuel a long-lived excited state, matching the energies of the respective states is paramount. In the case of oligothiophene based states, as observed in the ground state absorption spectra of the ligands (Figure 2-1), the lowest-lying excited state is expected to drop in energy significantly, with each additional ring. Incorporation of ligand phen-ttL (29) into a heteroleptic complex, [Ru(phen)2(phen-ttL)][PF6]2 (34, Chart 2-2) offers some insight into the significant photophysical changes instigated though varying the pendent thiophene length. 59   Figure 2-12. (a) Absorption spectrum of [Ru(phen)2(phen-ttL)][PF6]2 (34). (b) TA difference spectrum of 34 (CH3CN, λex = 355 nm, fwhm = 35 ps).  The ground state absorption spectrum of 34 (Figure 2-12a) exhibits features similar to those of the bithienyl analog [Ru(phen)2(phen-btL)][PF6]2 (33), with the marked exception that the terthiophene localized π  π* transition is at a low enough energy that it overlaps with the 1MLCT bands (λmax ≈ 390 nm). Excitation at these wavelengths results in population of both MLCT and LC states. Regardless of excitation wavelength, 34 is a non-emissive complex, with an exceptionally long excited state lifetime (τes > 50 μs). Along with comparison of Figure 2-12b to complexes previously reported in our research group featuring pendent terthiophene ligands,92 these data strongly suggest that the excited state formed in the 34 is a 3LC state localized on the terthienyl moiety.   These findings suggest that in Ru2+-polypyridyl complexes, bithienyl moieties are the optimal length oligothiophene if equilibration of 3MLCT and 3LC states is desired in the excited state. Such equilibrations may result in long-lived charge separated 3ILCT states (as in the case of 33 or 32) that may be accessed by follow-on reactions, and as such low-lying 3LC states may prove problematic in the design of photocatalytic molecular systems. (a) (b) 60  Section 2.3.4 – Electropolymerization of complexes bearing peripheral bithienyl moieties  Complexes bearing oligothiophenes may be polymerized electrochemically, giving rise to materials or films with longer conjugation lengths.71 [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen- btL)2(dppz)][PF6]2 (a complex discussed in Chapter 3; 50 Chart 3-2) were oxidatively polymerized (to give polymeric films, poly-32 and poly-50) by sweeping the working electrode (indium tin oxide; ITO) between 0 V and the onset of current (1.5 V vs. Ag wire) for a number of cycles. During sweeping the potential, a monotonic increase in current was observed upon successive sweeps (Figure 2-13a), indicative of polymerization114 and producing an orange film on the ITO electrode.   Figure 2-13. (a) Cyclic voltammogram showing the increase in current with successive scans of a CH3CN solution of [Ru(phen-btL)3][PF6]2 (32). (b) Absorption spectra of a solution of 32 (CH3CN) and a 10 scan film of poly-32 on an ITO substrate.  Poly-32 exhibited optical absorption properties similar to the monomeric species in solution (Figure 2-13b), suggesting the films retain photophysical properties similar to their parent monomers. Additionally, solid-state TA measurements performed on poly-32 gave an excited state spectrum (Figure 2-14) qualitatively similar to that recorded for monomeric 32 in (a) (b) 61  solution (Figure 2-3), suggesting the formation of a charge separated state in the film. Due to ablation of the films under laser irradiation, excited state lifetime data were impossible to obtain.  Figure 2-14. Solid-state excited state TA spectra of unfunctionalized ITO (red) and poly-32 (t = 0-200 ns, CH3CN, λex = 355 nm, fwhm = 35 ps).  Comparison by SEM of films poly-32 and poly-50 grown under identical conditions offers some insight into the film morphology differences obtained for the two different complexes. Poly-32 films appear smooth, while poly-50 films appear to have a fibrous surface morphology (Figure 2-15). This may be a result of the asymmetrical coordination sphere around the metal center 32.  62   Figure 2-15. SEM micrographs of 15 scan electrochemically grown films of (a) [Ru(phen- btL)3][PF6]2 (32) and (b) [Ru(phen-btL)2(dppz)][PF6]2 (50) on an ITO substrate.  In order to determine whether these films may be used as electrodes in photoelectrochemical synthesis (PES) cells to carry out the half-reactions of artificial photosynthesis (Section 1.2), films on ITO were used as the working electrode in a three electrode chronoamperometry experiment housed in a quartz cuvette (held at a potential of 0 V vs. Ag wire). The films were then irradiated with a handheld UV lamp (λem = 365 nm), and the current was monitored versus time. On irradiation, a current opposite of that observed for unfunctionalized ITO was observed in the cell (Figure 2-16). This current ceased once the lamp was turned off. It appears that on irradiation, charge carriers are formed in the film, suggesting these functionalized ITO electrodes may be used as electrodes in PES cells. (a) (b) 63   Figure 2-16. Chronoamperometry experiment with (a) poly-32 and (b) poly-50 in CH3CN with 0.1 M n-[Bu4N]PF6 (on an ITO substrate) with UV-light irradiation (λem = 365 nm, 0 V vs. Ag wire).  PES cells function by carrying out the half-reactions of artificial photosynthesis at separate electrodes in an electrochemical cell. The potential needed to drive the reactions is provided by light irradiation rather than by an external applied energy source. These cells require (stable) interfacial links to attached molecular assemblies, supporting electron transfer to and from the electrode. In PES cells, electrodes can function as either an electroactive interface (where the attached assembly acts as a conductive interface for transferring electrons between catalysts at separate electrodes resulting in an overall charge on the electrode surface) or as active components (where the electrode behaves as the initial electron acceptor rather than a unit in an assembly).5  Section 2.3.5 – Incorporation of oligothiophene ligands into cyclometalated Ir(III) complexes  Cyclometalated Ir3+ complexes are isostructural to Ru2+ polypyridyl complexes, and have found application in electron transfer arrays,115 photocatalytic hydrogen production,116 light (a) (b) 64  harvesting materials,117 and most notably as phosphorescent materials in organic light emitting diodes (OLEDs).118 Ir3+ cyclometalates have also been used in the fabrication of electroluminescent devices and light emitting electrochemical cells (LECs).119 To date, only one example of an Ir complex where a 3LC state is in equilibrium with a 3MLCT state has been reported in the literature.120  Chart 2-3.   In order to investigate whether phen-btL (28) may act as a ‘triplet reservoir’ in a system with a metal center other than Ru2+, the Ir3+ complexes 42-44 in Chart 2-3 were prepared via microwave-assisted synthesis. A number of isomers are possible for each complex and no efforts were made to isolate the individual isomers (one possible isomer of each complex is shown in Chart 2-3). The absorption spectra of these complexes are reminiscent of fac-Ir(ppz)3, 121 with the exception of the introduction of a π  π* band attributed to a bithienyl moiety observed in 44 (Figure 2-17). Contrary to fac-Ir(ppz)3 these complexes are all luminescent, from a 3MLCT state, albeit weakly in the case of 44. Other photophysical properties corresponding to these complexes are tabulated in Table 2-2.  65   Figure 2-17. Normalized absorption spectra of Ir3+ complexes 42-44 (CH3CN). Table 2-2. Photophysical properties of Ir3+ complexes with oligothiophene ligands Complex λem / nm a Φem b,f τem / μs c,d τes / μs (λ / nm) c,e [Ir(ppz)2(phen)][PF6] (42) 564 0.52 0.900 1.10 (385 – 408) 0.83 (508 – 531) [Ir(ppz)2(phen-tL)][PF6] (43) 573 0.27 0.800 0.81 (397 – 420) 0.78 (500 – 523) [Ir(ppz)2(phen-btL)][PF6] (44) 576 0.08 - 12.00 (412 – 442) 12.30 (534 – 638) aUncorrected, room temperature, CH3CN solution. bAbsolute quantum yield at room temperature. cSamples prepared in air and purged with Ar for 30 min. dλex = 453 nm. eλex = 355 (fwhm = 35 ps). fError estimated to be ≤ 10% based on prior experiments (Table 2-1).  It is clear from the data in Table 2-2 that an increase in the number of thienyl rings appended to the phenanthroline ligand results in a decrease in emission energy, and a decrease in  emission quantum yield. Additionally, 42 and 43 exhibit almost identical excited state and emission lifetimes (τem ≈ 1 μs), where 44, exhibits an excited state lifetime that is approximately 12 times longer than the aforementioned complexes. 66  Analogous to the discussion in Section 2.3.2, it is possible to attribute the bathochromic shift in emission wavelength in these complexes to one of two factors: a delocalization of the excited state electron onto the amide bridge, resulting in a longer path of conjugation; or to the electron donating character of the amide linkage (this is discussed in depth in Chapter 4). The decrease in quantum yield from 42 (0.52) to 43 (0.27) to 44 (0.08) may be attributed to formation of a second excited state close in energy, and equilibrating with the emissive 3MLCT state. Emissive heteroleptic cyclometalated Ir3+ complexes bearing ligands similar to ppz are expected to have emission (and therefore 3MLCT energies) that lie in close proximity to the energy previously reported for a 3LC state localized on the bithienyl moiety of 28 (2.2 eV).102,121,122 Based on this comparison, and the drastic increase in excited state life and decrease in quantum yield in 44, it is possible that two states may be equilibrating in the excited state of this complex.  Figure 2-18. TA difference spectra of cyclometalated Ir3+ complexes 42-44 (t = 78 – 127 ns, CH3CN, λex = 355 nm, fwhm = 35 ps).  67  An analysis of the excited state difference spectra of complexes 42-44 (Figure 2-18), reveals a trend similar to that observed in the homoleptic Ru2+ complexes reported in Section 2.3.2. Here, 42 and 43 appear to be behaving in a similar fashion in the excited state, while 44 exhibits features at both high and low energies of the spectrum that are comparable to those in [Ru(phen-btL)3][PF6] (32) and [Ru(phen)2(phen-btL)3][PF6] (33, Figure 2-3). These features correlate to the formation of a 3LC state on bithiophene, where emission of this complex, albeit weak, at 576 nm confirms the presence of a 3MLCT state. These two states, due to their energetic similarities, may be in equilibrium, with the 3LC state slightly lower in energy.  Triplet excitons that display a long lifetime are of use in solar energy conversion applications, by facilitating charge separation; and in general managing the interplay between peripheral organic components and metal centers of these types of complexes is important for a variety of applications.123-125 Investigations of Ir3+ cyclometalates bearing phen-tL (27) and phen- btL (28) ligands highlight the optimal properties of the bithienyl ligand in systems designed for the formation of long-lived excited states comprised of two or more interfacing states.  Section 2.4 – Conclusions   In most Ru-based triads, the lifetime of the second charge-separated state (typically an ILCT state) is on the order of 100-300 ns as back electron transfer is largely unimpeded (Section 1.2.2).126 In this chapter a series of Ru2+ and Ir3+ complexes with long excited state lifetimes have been discussed and it was determined that two factors extend this lifetime well into the microsecond regime. First, the 3LC state controls the rate of 3ILCT formation by regulating the amount of 3MLCT state present. Second, back electron transfer from the 3ILCT state to the ground state is non-radiative and a high energy process (-ΔGo ≥ 1.9 eV) that could easily exceed 68  the total back electron transfer reorganization energy, putting this process in the inverted Marcus region.86,127  The transient absorption spectra of complexes bearing phen-btL (28) ligands demonstrate that a bithienyl-based triplet state exists in equilibrium with both a 3MLCT and a charge- separated state where a hole is localized on the bithienyl moiety and an electron is localized on a phenanthroline moiety.   Electropolymerization of [Ru(phen-btL)3][PF6] (32) to give thin films may lead to applications of these films as electrodes in PES cells. Irradiation of these films leads to the formation of a current in an electrochemical cell, suggesting that these films may be used as electroactive interfaces to drive the catalytic half reactions of artificial photosynthesis. The results presented in this chapter advocate that further efforts to direct the charge- separation in Ru2+ complexes bearing phen-btL (28) combined with other acceptor ligands could lead to long-lived excited states in which charge separation is vectorial and readily accessible to follow-on reactions. To this end, Chapter 3 introduces a series of complexes bearing both phen- btL (28) ancillary ligands and large, planar, polypyridyl ligands that may behave as electron acceptors initiating the formation of states where charge separation is directional.    69  CHAPTER 3  Long-lived, directional photoinduced charge separation in Ru(II) complexes bearing laminate polypyridyl ligands  Section 3.1 – Introduction  The guiding principles behind the design of effective artificial systems for photochemical energy conversion are built on foundations established by electron transfer (ET) research and investigations into natural photosynthetic processes.   In Photosystem II, photoexcitation initiates a cascade of ET reactions spatially separating the electron-hole pair such that this energy can be used to drive multi-electron water oxidation and carbon fixation reactions.6 Attempts to mimic photosynthesis have led to the study of molecular donor-chromophore (D-C) or chromophore- acceptor (C-A) dyads, donor-chromophore-acceptor (D-C-A) triads (Chart 3-1), and more elaborate tetrads, pentads, and related multi-modular assemblies (Section 1.2.2).15,128-131 These assemblies are designed to support directional long-range electron transfer upon photoexcitation with the goal of producing high energy redox equivalents for follow-on reactions. Such efforts are still hampered by fast recombination rates and competing relaxation processes such as energy transfer, radiative and non-radiative decay.16,132 In general, charge separated (CS) states in molecular triads are relatively short lived, with lifetimes ranging from tens to hundreds of nanoseconds.106,133-135 In linear, rod-like D-C-A molecular triads (46) capable of directional charge separation, modest increases in charge separated state lifetimes (up to ≈ 1 µs) have been achieved by maximizing the separation distance of the electron-hole pair and have been further enhanced by applying some external perturbation (hydrogen bonding, for example).136,137 70  Chart 3-1. Ref. 128,136,137    One strategy to increase the lifetime of the charge separated state is via equilibration with other low-lying states.56 In this chapter, bithienyl moieties (shown previously to possess low- lying triplet states) are paired with Ru2+ polypyridyl complexes containing ‘laminate’138 acceptor ligands (Chart 3-2): dipyrido[3,2-a:2',3'-c]phenazine (47, dppz), tetrapyrido[3,2-a:2',3'-c:3'',2''- h:2''',3'''-j]phenazine (48, tpphz), and 9,11,20,22-tetraazatetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3''']- pentacene (49, tatpp).  Laminate acceptor ligands have two or more acceptor orbitals that are delocalized over the entire ligand (laminated over each other) but interact with the metal such that one orbital defines the ground state optical properties of the complex (referred to as the ‘optical’ molecular orbital) and the other orbital defines the ground state reduction potentials (referred to as the ‘redox’ molecular orbital).138-140  In the excited state, these two acceptor MOs 71  participate to give 3MLCTprox (involving an orbital proximal to the metal center) and 3MLCTdist (involving an orbital distal to the metal center) states, either of which may dominate the excited state properties of the complex depending on solvent, secondary coordination sphere, protonation, or in the case of tatpp (49) and tpphz (48) ligands; metalation at the open end.141-146  Thus in the MLCT excited state, the laminate ligands offer two potential sites of electron storage with the distal site formally storing an electron spatially further away from the Ru3+ center.   Chart 3-2.   In this chapter, a series of D-C-A triads (Chart 3-2) prepared by incorporating amide- linked bithienyl donor ancillary ligands (28) and a series of linear acceptor ligands into Ru2+ complexes 50-52 is introduced.  Here, bithienyl moieties may act as reductive quenchers for Ru3+ formed on photoexcitation and the excited electron may be directed to either the proximal or distal MO on the acceptor ligand. If the electron is directed to the distal MO, the resulting inter-72  ligand charge transfer (ILCT) state would nominally represent a charge-separated state with 11 to 14 Å (center of the acceptor ligand to the center of the bithienyl moiety) separating the electron-hole pair, a distance at which back electron transfer (BET) may be slowed.147 In some cases, incorporation of bithienyl groups may introduce additional low-lying 3LC states that can extend the lifetime of low-lying CS states via excited state equilibration (the ‘triplet reservoir’ effect),61 making the CS state available to follow-on reactions and making the triads useful models for the study of biomimetic photoinduced electron transfer.  Section 3.2 – Experimental  Section 3.2.1 – General  NH4PF6 (Alfa), RuCl3·xH2O (Strem), 1,10-phenanthroline hydrate (Alfa), and Zn(OTf)2 (used in spectroscopic experiments, Strem) were purchased from commercial sources and used as received. The preparation of ligand phen-btL (28) has been discussed in Chapter 2, while the preparation of ligand tL (77) is described in Chapter 4. All solvents were used as received, unless noted. Silica gel used in purification was purchased from Silicycle (SiliaFlash F60 or G60). Complexes Ru(phen-btL)2Cl2 (41, Section 2.2.3) 148 and [Ru(phen-btL)2(1,10- phenanthroline-5,6-dione)][PF6]2 (55), 149 were prepared using modified literature procedures. [Ru(phen)2(tpphz)][PF6]2 (53) and [Ru(phen)2(tatpp)][PF6]2 (54) were prepared in the labs of Dr. F. M. MacDonnell (University of Texas, Arlington) and were used for spectroscopic measurements as received.  1H and 13C NMR spectra were obtained on either a Bruker AV-300, Bruker AV-400Direct or Bruker AV-400Indirect spectrometer. All chemical shifts in 1H and 13C spectra were 73  referenced to residual solvent, and the splitting patterns are designated as s (singlet), d (doublet), t (triplet), m (multiplet) or br (broad). NMR solvents (Cambridge Isotope Laboratories or Sigma) were used as received. ESI-MS (Bruker Esquire), and MALDI-TOF MS (Bruker Biflex IV) were acquired at the UBC Microanalysis facility. Transmission electron microscopy micrographs were obtained on a Hitachi H7600 Transmission Electron Microscope at the UBC Bioimaging Facility. UV/Vis absorption spectra were obtained with a Varian Cary 5000 using Fisher (HPLC Grade) solvents. Fluorescence data were collected on a Photon Technology International (PTI) fluorimeter using a 75 W Xe arc lamp as the source. Absolute quantum yields were determined using an integrating sphere coupled to the PTI fluorimeter. Fluorescence lifetime measurements and transient absorption experiments were carried out as described in Section 2.2.2. Electrochemical data were obtained on a CHI620C electrochemical analyzer (CH Instruments, Austin, TX, USA). A single-compartment, three-electrode electrochemical cell was used with either a glassy carbon (1.5 mm diameter disk) or platinum (1.0 mm diameter disk) from Cypress Systems as working electrode.  Immediately before use, the electrode was polished to a mirror finish with wet alumina (Buehler, 0.05 m), followed by rinsing with Millipore Milli- Q water and sonication. A Pt wire and a non-leak Ag/AgCl, satd KCl reference electrode (Cypress Systems, model EE009) were used as counter and reference electrodes, respectively.  All potentials were measured and are quoted vs. Ag|AgCl|satd. KCl reference electrode. All electrochemical data were recorded in acetonitrile with 0.1 M Bu4NPF6 as supporting electrolyte. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the electrochemical characterization of respective complexes. Transmittance spectroelectrochemical measurements were performed at constant potential in a quartz thin-layer compartment 74  containing a platinum minigrid as working electrode. The liquid thin layer was spectroscopically probed as a function of time by using a diode array spectrometer (Hewlett-Packard model 8453).  The counter electrode (platinum wire) and the Ag/AgCl reference electrode were placed in the quartz cuvette near to the thin layer compartment.   Section 3.2.2 – General procedures for preparation of organic precursors required for the synthesis of metal complexes bearing dppz, tpphz and tatpp ligands  The ligand dipyrido[3,2-a:2',3'-c]phenazine (47, dppz) used in the preparation of [Ru(phen- btL)2(dppz)][PF6]2 (50) was prepared from condensation of 1,10-phenanthroline-5,6-dione (56) and o-phenylenediamine (Eastman Organic Chemicals), in 95% EtOH as reported by Collins et al.150 The product was recrystallized from hot MeOH. Oxidation of 1,10-phenanthroline with H2SO4/HNO3 in the presence of KBr gave 1,10-phenanthroline-5,6-dione (56) in high yield. 151 Complexes bearing tpphz (48) require the synthesis of 5,6-diamino-1,10-phenanthroline (58). This diamino precursor was prepared using reported methods illustrated in Scheme 3-1. Synthetic Scheme 3-1 was adapted from Launey and coworkers, with slight modifications.152 5- nitro-1,10-phenanthroline (39) was prepared by nitration with fuming HNO3 in H2SO4. 101 Reaction of 5-nitro-1,10-phenanthroline with hydroxylamine hydrochloride in EtOH/dioxan afforded 5-nitro-6-amino-1,10-phenanthroline (57).153 Reduction of the nitro group at the 5- position with 10% Pd/C (Sigma) and hydrazine (Aldrich) gave the target 5,6-diamino-1,10- phenanthroline (58, as determined by comparison of 1H NMR spectra and mass spectrometry results to those reported in literature).153   75  Scheme 3-1.   A synthetic scheme for the preparation of dipyrido[3,2-a:2',3'-c]phenazine-11,12-diamine (63, dadppz) is shown in Scheme 3-4. A number of modified literature procedures were used in the synthesis of this compound. Briefly, o-phenylenediamine was protected with tosyl groups (59),154 then nitrated at the 4 and 5 positions with fuming HNO3 in glacial CH3COOH (60). 155 Reduction of the nitro groups was performed using Sn in HCl (61).156 Condensation of this N,N'- (4,5-diamino-1,2-phenylene)bis(4-methylbenzenesulfonamide) product with 1,10- phenanthroline-5,6-dione (56) in MeOH gave the tosylated dadppz (62) product in quantitative yield. The protecting groups were removed in H2SO4, to give dadppz (63) as a red solid. 157   Section 3.2.3 – Methods  [Ru(phen-btL)(1,10-phenanthroline-5,6-dione][PF6]2 (55)  Ru(phen-btL)2Cl2 41 (70 mg, 0.074 mmol) and 56 (19 mg, 0.089 mmol) were suspended in 20 mL 1:1 EtOH:H2O. This suspension was purged with N2 for 15 minutes, and heated to reflux under N2 for 19 hours. The mixture was cooled to room temperature, concentrated under reduced pressure and treated with a saturated solution of NH4PF6(aq). The resulting brown precipitate was collected by filtration, dried in air, and purified by silica gel column chromatography (96:3:1) with CH3CN:H2O:KNO3(aq) as eluent. The major orange/brown band was collected, concentrated under reduced pressure and treated with a minimal amount of saturate NH4PF6(aq) resulting the 76  formation of a dark orange/brown precipitate as the title compound. Yield: 20 mg (20 %). 1H NMR (400 MHz, CD3CN) δ ppm 7.10 - 7.17 (m, 1 H) 7.39 (t, J=4.42 Hz, 1 H) 7.44 (t, J=3.35 Hz, 1 H) 7.47 - 7.57 (m, 2 H) 7.58 - 7.68 (m, 1 H) 7.77 - 7.87 (m, 1 H) 7.94 (dd, J=8.22, 3.96 Hz, 2 H) 8.01 (d, J=5.18 Hz, 1 H) 8.28 (t, J=3.81 Hz, 1 H) 8.36 (t, J=3.81 Hz, 1 H) 8.47 - 8.55 (m, 2 H) 8.58 (d, J=8.22 Hz, 1 H) 8.70 (dd, J=15.99, 8.38 Hz, 1 H) 8.81 (d, J=8.22 Hz, 1 H) 9.37 (d, J=10.66 Hz, 1 H). ESI MS m/z 1231.3 ([M+PF6] +).  [Ru(phen-btL)2(dppz)][PF6]2 (50)  The ligand dppz 47 (40 mg, 0.14 mmol) was suspended in 10 mL EtOH:H2O (7:3), the mixture was purged with N2 (10 mins) and then heated to reflux to dissolve the dppz. Under a constant flow of N2, Ru(phen-btL)2Cl2 (120 mg, 0.13 mmol) was added, and the reaction mixture was left to reflux under N2 for 18 hours. The reaction mixture turned deep red, and after the reaction period a bright red solid formed on addition of a minimal amount of saturated NH4PF6(aq). This red solid was collected, and purified via silica gel column chromatography with CH3CN/H2O/KNO3(aq) (96:3:1) as eluent. The major orange/red band was collected, concentrated under reduced pressure, and the title complex was precipitated as an orange solid through the addition of a minimal amount of NH4PF6(aq). Yield: 0.051 g (27 %). 1H NMR (400 MHz, CD3CN) δ ppm 7.13 (dt, J=5.18, 3.50 Hz, 1 H), 7.36 - 7.41 (m, 1 H), 7.44 (t, J=3.35 Hz, 1 H), 7.48 (dt, J=3.27, 1.87 Hz, 1 H), 7.61 - 7.74 (m, 2 H), 7.77 - 7.87 (m, 1 H), 7.91 - 7.95 (m, 1 H), 8.02 - 8.06 (m, 1 H), 8.11 - 8.20 (m, 3 H), 8.24 - 8.28 (m, 1 H), 8.49 (dd, J=6.40, 3.35 Hz, 1 H), 8.52 (s, 1 H), 8.61 (d, J=8.22 Hz, 1 H), 8.74 (ddd, J=8.53, 3.65, 0.91 Hz, 1 H), 9.31 (d, J=2.13 Hz, 1 H), 9.67 (dd, J=8.22, 1.22 Hz, 1 H). 13C NMR (150.92 MHz, CD3CN) δ ppm 121.59, 121.65, 124.05, 124.89, 125.30, 125.74, 126.47, 126.84, 127.34, 128.11, 129.19, 130.71, 130.36, 132.08, 133.09, 133.22, 135.38, 136.17, 139.59, 142.31, 142.97, 145.81, 147.8, 150.40, 152.07, 77  152.30, 152.96, 153.12, 153.81, 160.66. HR-ESI MS m/z [M]+ calcd for C60H36N10O2F6PS4Ru, 1300.0610; found, 1300.0607 (0.2 ppm).  [Ru(phen-btL)2(tpphz)][PF6]2 (51)  Complex 55 (20 mg, 0.015 mmol) was dissolved in 5 mL of CH3CN. The solution was purged with N2 (10 mins) and then 58 (5 mg, 0.017 mmol) was added as a solution in 5 mL of MeOH (that had also been purged with N2 for 10 mins). The combined solutions were heated to reflux for 12 hours, cooled to room temperature, and then filtered to remove any insoluble impurities. The resulting filtrate was concentrated under reduced pressure, and then treated with a small amount of saturated NH4PF6(aq) to give the title complex as a bright orange solid. The complex was isolated by filtration, washed with (2 mL) H2O, EtOH and Et2O and used without further purification. Yield: 17 mg (77%). 1H NMR (with 5 eq. Zn2+, 400 MHz, CD3CN) δ ppm 7.11 (m, 1 H), 7.39 (m, 3 H), 7.68 (m, 2 H), 7.82 (m, 1 H), 7.94 (m, 3 H), 8.29 (m, 1 H), 8.39 (dd, J=8.22, 4.87 Hz, 1 H), 8.50 (m, 1 H), 8.60 (d, 1 H), 8.75 (m, 1 H), 9.37 (d, J=4.87 Hz, 1 H), 9.47 (br s, 1 H), 9.96 (d, J=7.31 Hz, 1 H), 10.23 (d, J=8.53 Hz, 1 H). 13C NMR (with 5 eq. Zn2+, 100.63 MHz, CD3CN) δ ppm 123.72, 125.88, 126.90, 127.09, 127.57, 128.25, 128.70, 129.71, 129.91, 131.40, 132.04, 132.24, 135.01, 135.47, 137.22, 138.03, 141.56, 141.78, 143.67, 144.75, 148.44, 149.29, 149.63, 151.61, 152.07, 154.99, 156.38, 158.92, 159.12, 161.62. HR-ESI MS m/z [M]+ calcd for C66H38N12O2F6PS4Ru, 1402.0818; found, 1402.0825 (-0.5 ppm).  [Ru(phen-btL)2(tatpp)][PF6]2 (52)   Complex 55 (20.0 mg, 0.015 mmol) was dissolved in 15 mL of CH3CN and added dropwise to a solution of 63 (5.5 mg, 0.017 mmol) in 60 mL of 1:1 glacial acetic acid:EtOH 78  heated to reflux. The suspension was heated to reflux for 12 hrs and then filtered hot. The filtrate was concentrated to ca. 15 mL and a saturated solution of NH4PF6(aq) was added resulting in precipitation of a dark brown solid. The solid was isolated by filtration and washed with small volumes (2 mL) or H2O, EtOH and Et2O. This product was used without further purification. Yield: 19 mg (79%). 1H NMR (with 5 eq. Zn2+, 400 MHz, CD3CN) δ ppm 7.14 (m, 1 H), 7.40 (m, 1 H), 7.45 (t, J=4.42 Hz, 1 H), 7.49 (t, J=4.72 Hz, 1 H), 7.70 (m, 2 H), 7.87 (ddd, J=8.15, 5.25, 3.35 Hz, 1 H), 7.95 (t, 4.26, 1 H), 8.05 (m, 1 H), 8.13 (m, 1 H), 8.19 (t, 1 H), 8.27 (m, 1 H), 8.35 (d, J=5.48 Hz, 1 H), 8.53 (d, J=9.75 Hz, 1 H), 8.64 (dd, J=8.38, 3.50 Hz, 1 H), 8.77 (d, J=8.83 Hz, 1 H), 8.99 (d, J=4.26 Hz, 1 H), 9.37 (d, J=2.74 Hz, 1 H), 9.73 (m, 2 H), 10.05 (d, J=7.92 Hz, 1 H). HR-ESI MS m/z [M - H]+ calcd for C72H39N14O2S4Ru, 1358.1294; found, 1358.1323 (-2.1 ppm).  [Ru(tL)2(tatpp)][PF6]2 (64)  [Ru(tL)2(1,10-phenanthroline-5,6-dione)][PF6]2 (50 mg, 0.040 mmol) and 63 (14 mg, 0.044 mmol) were dissolved in 9 mL CH3CN:THF:CH3COOH (1:1:1) that had been purged with N2 for 15 minutes. The reaction mixture was heated at 90°C for 6 hrs. After the reaction time, the mixture was cooled to room temperature, and the mixture was centrifuged to remove any insoluble impurities. The liquid phase was decanted, and a minimal amount of saturated NH4PF6(aq) was added. The brown precipitate that formed was collected by vacuum filtration. The collected solid was dissolved in CH3CN and filtered again to remove any insoluble solids. The filtrate was collected and the solvent was removed under reduced pressure to yield the title complex as a red-brown solid. Yield: 43 mg (71%). 1H NMR (400 MHz, CD3CN)  ppm 7.22 - 7.35 (m, 2 H) 7.51 (d, J=6.14 Hz, 1 H) 7.68 (d, J=5.26 Hz, 1 H) 7.74 (d, J=4.97 Hz, 1 H) 7.80 (d, 79  J=5.55 Hz, 1 H) 7.88 - 7.98 (m, 4 H) 8.02 (d, J=3.80 Hz, 1 H) 8.32 (br. s., 1 H) 8.36 (d, J=5.55 Hz, 1 H) 8.85 (d, J=11.40 Hz, 2 H) 9.23 (br. s., 1 H) 9.61 (br. s., 1 H) 9.69 (d, J=7.89 Hz, 1 H) 9.98 (br. s., 1 H). MALDI-TOF MS m/z 1373.3 ([M + PF6] +).  Section 3.3 - Results and discussion  Section 3.3.1 - Synthesis and characterization  The synthesis of ligand phen-btL (28) is described in a previous chapter (Section 2.2.3), and reported in literature.158 To prepare complex [Ru(phen-btL)2(dppz)][PF6]2 (50), chelating ligand dppz (47) was synthesized through condensation of 1,10-phenanthroline-5,6-dione (56, separately prepared via the oxidation of 1,10-phenanthroline with H2SO4/HNO3) with o- phenylenediamine (Scheme 3-2).150 This method gave dppz (47) in almost quantitative yield, and the product was further purified through multiple recrystallizations.   Scheme 3-2.   Complex 50 was obtained through reaction of Ru(phen-btL)2Cl2 (41) with dppz (47) in EtOH/H2O (Scheme 3-2). The product was purified by silica gel column chromatography (96:3:1 CH3CN:H2O:KNO3(aq)), and isolated as a hexafluorophosphate salt. A number of isomers of this 80  complex are possible, both through the asymmetric nature of the ligand, and the possibility of Δ- or Λ- isomers through the octahedral geometry of the metal center; no effort was made to isolate or characterize the individual isomers and all spectroscopic measurements were carried out on what is likely to be a mixture of these isomers. 1H NMR spectra were indicative of a symmetrical species, confirming the expected C2 symmetry of immediate coordination sphere surrounding the metal center.  Due to the two possible metal binding sites on bridging ligands such as tpphz (48) and tatpp (49), synthesis of mononuclear metal complexes of this type is challenging. Even at high dilutions, attempts to synthesize mononuclear complexes using a similar approach to the one employed in the preparation of 50 were unsuccessful. As a result, a ‘chemistry on the metal’ approach was utilized, where [Ru(phen-btL)2(1,10-phendione-5,6-dione)][PF6]2 (55) was condensed with the appropriate diamino precursor (either 63 or 58) to give the desired tatpp or tpphz product. In the case of tpphz complex [Ru(phen-btL)2(tpphz)][PF6]2 (51), 55 was condensed with 5,6-diamino-1,10-phenanthroline (58, Scheme 3-1) in CH3CN/MeOH (Scheme 3-3). The identity of the resulting product was difficult to confirm by NMR techniques, as these complexes have been shown to aggregate via π-π interactions of the tpphz ligands, as evidenced through the broadening of many of the resonances.159     81  Scheme 3-3.  The diamino precursor required for synthesis of tatpp complexes, dipyrido[3,2-a:2',3'- c]phenazine-11,12-diamine (63, dadppz), was prepared using a stepwise approach (Scheme 3-4). For most of the steps, synthesis proceeded as reported in literature. Particularly problematic was the reduction of N,N'-(4,5-dinitro-1,2-phenylene)bis(4-methylbenzenesulfonamide) (60) to the diamino precursor N,N'-(4,5-diamino-1,2-phenylene)bis(4-methylbenzenesulfonamide) (61). Ultimately, reduction with Sn in HCl proved to be the most effective, albeit low yielding, method for this transformation.156 The final deprotection step in H2SO4 gave dadppz (63) as a red-brown solid that was characterized by 1H NMR and mass spectrometry, and confirmed by comparison to literature.157           82   Scheme 3-4.    [Ru(phen-btL)2(tatpp)][PF6]2 (52) was prepared via condensation of 55 with 63 in CH3CN/glacial CH3COOH/EtOH (Scheme 3-5). The final product was isolated as a hexafluorophosphate salt and the structure was confirmed by NMR spectroscopy and high resolution mass spectrometry.  Scheme 3-5.   83   Figure 3-1. (top) Portion of the 1H NMR spectrum of [Ru(phen-btL)2(tatpp)][PF6]2 (52) prior to addition of Zn2+ and (bottom) portion of the 1H NMR spectrum of 52 with 5 eq. of Zn2+ (CD3CN, 400 MHz, 24.9°C).  At moderate concentrations [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen- btL)2(tatpp)][PF6]2 (52) show broad 1H NMR signals associated with aggregation via π-π stacking of the polypyridyl tpphz and tatpp moieties.159 To resolve the 1H NMR spectra, 5 eq. of Zn2+ as Zn(OTf)2 was added to prepared 1H NMR samples which has the effect of coordinating the open end of the complex and breaking up the π-π stacking as evidenced by a sharpening of the NMR peaks (Figure 3-1). Additional evidence for aggregation was observed in transmission electron microscopy (TEM) images of solutions that were drop-cast onto carbon film/copper mesh TEM grids from CH3CN. In samples cast from a solution of [Ru(phen-btL)2(tatpp)][PF6]2 (52) with 5 eq. Zn2+ present, TEM images showed fibrous, uniform structures throughout the grid. In samples cast from a solution of 52 in the absence of Zn2+, more bulbous fibers were observed (Figure 3-2). The bulbous nature of the latter may be attributed to π-π interactions in 84  tatpp units that without Zn2+ coordination are expected to be planar; there are a number of nanoscopic structures possible from these interactions, including columns and stacks.     Figure 3-2. TEM micrographs of (a) [Ru(phen-btL)2(tatpp)][PF6]2 (52) with 5 eq. Zn 2+ and (b) 52 without Zn2+ cast from CH3CN. Vacc = 80.0 kV.  Section 3.3.2 - Electrochemical evaluation  Electrochemical data for complexes 32, 50-54 and relevant related complexes are collected in Table 3-1 and schematically represented in Figure 3-3.  The data in Table 3-1 was predominantly obtained by either CV or DPV techniques, however in some instances, the reductive processes in the dppz and tatpp-based complexes are not clearly observed by these techniques and are only detected as minor quasi-irreversible waves; particularly tatpp complexes in the presence of Zn2+.* This difficulty may be associated with poor surface electron-transfer kinetics and/or absorption effects.  It is clear that a redox process is occurring in many such cases, as we observe clear optical changes in the absorption spectra using transmittance                                                           *  These electrochemical experiments were performed at the University of Texas, Arlington by Dr. Norma de Tacconi, a member of the Dr. F. M. MacDonnell research group. 85  spectroelectrochemical (SEC) techniques.  It is then practical to estimate the potential of a poorly defined redox process in CV or DPV via SEC, which tracks the spectral changes of solution species. These data are included in Table 3-1 and are specifically noted.   Figure 3-3. Schematic comparison of the redox potentials of the reported complexes; Ru2+/3+ oxidation (filled circles), bithienyl oxidation (unfilled circles), ligand based reductions associated with the distal (redox) MO (squares) and proximal (optical) MO (triangles).   86   Table 3-1 Redox potentials for the oxidation (Eox) and reduction (Ered) of 30, 32, 50-54, 65-68. Complex Eox (Ru2+/3+) Eox (BT0/+) Ered Redox MO Ered Optical MO [Ru(phen)3] 2+  (30) 160 1.35  -1.37 -1.37 [Ru(phen-btL)3][PF6]2 (32) 158 1.35 1.25 -1.50 -1.50 [Ru(phen-btL)2(dppz)][PF6]2 (50)   -0.98 (a) -1.19 [Ru(phen)2(dppz)][PF6]2 (65) 1.38  -0.83, -1.28 -1.46 [Ru(phen-btL)2(tpphz)][PF6]2 (51) 1.37 1.24 -0.77, -1.06 -1.53 [Ru(phen-btL)2(tatpp)][PF6]2 (52) 1.37 1.25 -0.28/-0.33 (a,b), -0.47/-0.44(a,b) -1.19 [Ru(phen)2(tpphz)][PF6]2 (53) 161  1.38  -0.82 -1.28 [Ru(phen)2(tatpp)][PF6]2 (54) 162  1.33  -0.30, -0.83 -1.38 [(phen)2Ru(tpphz)Ru(phen)2] 4+ (68) 161 1.38  -0.67 -1.27 [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66) 162 1.39  -0.22, -0.71 -1.28 ‘Zn(tatpp)Zn’4+ adduct (67) 163   0.04, -0.25  All potentials (V) are quoted versus Ag/AgCl reference electrode in CH3CN except potentials for 51 which are quoted versus Ag/AgNO3 (a)Data estimated from SEC data. (b)Splitting of the first redox process due to π-π stacking.162  It is well-established that the energies of MLCT absorption energies in most Ru2+ polypyridyl complexes correlate linearly with the difference between the electrochemical potentials for (metal-centered) oxidation and (ligand-centered) reduction.20 In these cases, the redox MO and the optical MO are the same.  In complexes with laminate acceptor ligands, it is generally the second or third reduction potential that reveals the energy of the optical MO and these values are perturbed to more negative potentials than anticipated due to Coulombic effects.  Nevertheless, the difference in the Ru2+/3+ potential and the reduction potential of the proximal (or optical) MO corresponds well with the optical data (1MLCTprox typically centered at 460 nm).  The observation of the redox MO reduction prior to reduction of the optical MO is a clear measure that the redox MO is the ground state LUMO.  Complexes with bithienyl (BT) moieties 87  also exhibit an irreversible oxidative process associated with the BT0/+ couple at approximately +1.25 V, assigned to formation of the bithienyl radical cation and subsequent polymerization reactions.158 This process is observed prior to and overlapping with the Ru2+/3+ couple (typically observed at 1.35 V) indicating that the HOMO in bithienyl adducts is the bithiophene MO, not the Ru dπ MOs.  It is apparent from the optical data (Figure 3-4) that the Ru dπ MO acts as the donor orbital in the observed lowest energy optical transitions (i.e. the 1MLCT bands centered at 460 nm).   Section 3.3.3 - Ground state optical properties   Figure 3-4. Absorbance spectra of complexes 50-52 in CH3CN. 88   Figure 3-5. (a) Normalized absorbance spectra of [Ru(phen)2(tpphz)][PF6]2 (53) and [Ru(phen- btL)2(tpphz)][PF6]2 (51), and (b) complexes [Ru(phen)2(tatpp)][PF6]2 (54) and [Ru(phen- btL)2(tatpp)][PF6]2 (52) in CH3CN.  As previously described, laminate acceptor ligands have two or more acceptor orbitals that interact with the metal such that one orbital, the ‘optical’ molecular orbital, defines the ground state optical properties of the complex and the other orbital, the ‘redox’ molecular orbital, defines the ground state reduction potentials. For example, the lowest energy 1MLCT transition (~2.7 eV) in [Ru(phen)2(dppz)] 2+ (65) is assigned to a Ru dπ  π* (dppz LUMO+1) transition while the reduction process for the [Ru(phen)2(dppz)] 2+/+ couple occurs at -0.83 V vs. Ag/AgCl (Table 3-1) and is assigned to population of the LUMO localized on dppz.164  In this case the LUMO+1 corresponds to the optical orbital where the majority of the orbital density is localized on the bipyridine-like portion responsible for metal chelation and for this reason it is also referred to as the proximal molecular orbital.  The LUMO (or redox molecular orbital) is one where the majority of the orbital density is localized on the ‘phenazine-like’ or distal portion of the dppz ligand (also referred to as the distal MO).  (a) (b) 89  The ground state absorption spectra of complexes 50-52 (Figure 3-4) exhibit features analogous to those of their unsubstituted analogs, [Ru(phen)2(dppz)] 2+ (65),164 [Ru(phen)2(tpphz)][PF6]2 (53), and [Ru(phen)2(tatpp)][PF6]2 (54, Figure 3-5). Absorption spectra of 50-52 exhibit moderately intense Ru dπ  π* 1MLCT transitions in the visible region (centered around 460 nm).  Because the energy of these transitions are essentially identical to the corresponding 1MLCT transitions in [Ru(phen)3] 2+, they can be assigned to the 1MLCTprox state in which the electron resides in a ‘bpy-like’ proximal MO.  MLCT transitions between the Ru2+ dπ (HOMO)  π* redox or distal MO are expected to be of considerably lower energy on the basis of electrochemical measurements and are not observed in any of the complexes. The UV region of these spectra is dominated by LC transitions, with a strong bithiophene π  π* transition centered at 355 nm. In complexes [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen- btL)2(tatpp)][PF6]2 (52), this bithiophene transition overlaps with LC transitions localized on tpphz (48) and tatpp (49) moieties. Additionally tatpp complexes (52, 54, and [(phen)2Ru(tatpp)Ru(phen)2][PF6]2 66) all exhibit an intense structured band at 445 nm overlapping with the 1MLCTprox transition. 143 Coordination of Zn2+ to the open chelation site in 51-54, causes only minor perturbations in the visible region of the ground state absorption spectra (Figure 3-6). It becomes clear however, that this coordination has a significant effect on the excited state relaxation processes.  90   Figure 3-6. Absorbance spectra of (a) [Ru(phen-btL)2(tpphz)][PF6]2 (51) and (b) [Ru(phen- btL)2(tatpp)][PF6]2 (52) with and without 5 eq. of Zn 2+ as Zn(OTf)2 in CH3CN.  Section 3.3.4 - Excited state properties  Complexes bearing dppz (47) and tpphz (48) ligands are well studied largely due to the ‘light-switch effect,’ referring to the observation that bright emission from the 3MLCTprox state is observed in aprotic solvents or when the complex is intercalated into DNA.146,165 In protic solvents, these complexes are only weakly emissive due to the low quantum yield of emission associated with the 3MLCTdist state (the dominant state in protic environments). 140,166 The mechanism of this switching effect is still contested; however, it is clearly dependent on the solvent dipole and H-donor capacity.140,142,145,164,166-171 From the temperature dependence of the luminescence in CH3CN, Brenneman and coworkers have shown that the excited state equilibrium between the 3MLCTprox and 3MLCTdist states in [Ru(phen)2(dppz)] 2+ (65) is shifted to the proximal state due to entropic effects, illustrating how energetically close the two states are in this medium.145 In some cases, the lifetimes of these 3MLCT states are also enhanced through excited-state equilibration with ligand-centered (3LC) states on the laminate ligands.  For (a) (b) 91  example, the lifetime of the 3MLCTdist state in [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66) is extended to 1.3 μs in CH2Cl2 via equilibration with a 3LC state on the tatpp (49) ligand.143  While the lowest energy excited state is largely 3LC in nature, the complex retains much of the reactivity and excited state properties of the 3MLCT state. Excitation of the complexes presented in this chapter at wavelengths corresponding to their lowest-lying transitions, typically the 1MLCT transitions, results in emission centered at 610 nm in [Ru(phen-btL)2(dppz)][PF6]2 (50), [Ru(phen-btL)2(tpphz)][PF6]2 (51), and [Ru(phen)2(tpphz)][PF6]2 (53), while complexes [Ru(phen-btL)2(tatpp)][PF6]2 (52) and [Ru(phen)2(tatpp)][PF6]2 (54) exhibit no detectable emission. The energy of the emission in 50 and 51 matches that observed for related complexes without bithienyl groups, [Ru(phen)2(dppz)] 2+ (65) and 53, that has previously been assigned to emission from a 3MLCTprox state. 161,164 Addition of Zn2+ to 51 and 53 reduces the intensity of emission and shifts the emission maximum to 660 nm (Figure 3-7); this is indicative of switching emission from the 3MLCTprox to the 3MLCTdist state.  This metalation-induced switching effect was previously reported for the bpy analogue of [Ru(phen)2(tpphz)][PF6]2 (53), [Ru(bpy)2(tpphz)] 2+ (69) when bound to DNA.170 The ruthenium dimer, [(phen)2Ru(tpphz)Ru(phen)2] 4+  (68), represents the extreme case which is permanently metalated at both ends and emission from 68 at ~710-740 nm  has been interpreted as emission from the 3MLCTdist state. 170,172 Complexes [Ru(phen- btL)2(tatpp)][PF6]2 (52) and [Ru(phen)2(tatpp)][PF6]2 (54) remain non-emissive when Zn 2+ is added, which is consistent with this 3MLCTdist state always lying significantly lower in energy than the 3MLCTprox in complexes incorporating tatpp.   The lack of emission is due to the low energy nature of this state, which may be expected to emit in the near IR region or decay rapidly and non-radiatively. 92   Figure 3-7. Emission spectra for (a) [Ru(phen-btL)2(tpphz)][PF6]2 (51) in the absence (blue) and presence (orange) of Zn2+ as Zn(OTf)2 and (b) the same spectra collected after purging the sample with Ar for 15 minutes (λex = 450 nm, CH3CN).  Determining the exact nature of the excited state in these complexes requires analysis of luminescence lifetimes (τem) along with quantum yields (Φem) and excited state lifetimes (τes) measured by time resolved transient absorption (TA) spectroscopy (Table 3-2).  Where data exist for both τem and τes, the values are generally in good agreement.  Importantly, τes data offers insight into excited state processes even when the compound is non-emissive.  (a) (b) 93  Table 3-2. Summary of photophysical properties of complexes reported in this chapter Compound λem (nm) Φem e τem (µs) a τes (µs) b [Ru(phen)3][PF6]2 (30) 600 0.036 d 0.523 0.528 [Ru(phen-btL)3][PF6]2 (32) 158 600 0.072 7.4 6.2 [Ru(phen-btL)2(dppz)][PF6]2 (50) 615 0.110 2.2 2.2 [Ru(phen)2(dppz)] 2+ (65) 600164 0.033164 0.66164  [Ru(phen-btL)2(tpphz)][PF6]2 (51) 614 0.044 d 3.6 (0.27) 4.5 (388 - 488 nm) 3.5 (520 - 650 nm)  [Ru(phen-btL)2(tpphz)][PF6]2 + Zn (51Zn) 661   0.095 (433 - 483 nm) 0.131 (570 - 620 nm) [Ru(phen-btL)2(tatpp)][PF6]2 (52)     5.8 – 7.0 c [Ru(phen-btL)2(tatpp)][PF6]2 + Zn (52Zn)     0.10 – 0.15c [Ru(phen)2(tpphz)][PF6]2 (53) 604 0.073 161 0.900 0.891 [Ru(phen)2(tpphz)][PF6]2 + Zn (53Zn) 658   0.081 (433 - 483 nm)  0.090 (570 - 620 nm) [Ru(phen)2(tatpp)][PF6]2 (54)    0.35 – 0.55 c [Ru(phen)2(tatpp)][PF6]2 + Zn (54Zn)    0.004 [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66)    0.005 (CH3CN) 1.30 (CH2Cl2) 143 ‘Zn(tatpp)Zn’4+ adduct (67)    30 143 All measurements recorded in CH3CN unless otherwise noted, solutions prepared in air and then purged with Ar for 15 mins. aλex = 453 nm. bλex = 355 nm. cDifferent regions of the spectrum have differing lifetimes. dCalculated by comparison to [Ru(bpy)3] 2+ (1) 104. eError estimated to be ≤ 10% based on prior experiments (Table 2-1).   Over the series of complexes, there is a tremendous variation in excited state lifetimes as measured by emission and TA methods.  Significantly, complexes with appended bithienyl groups exhibit considerably longer lifetimes than their unsubstituted analogs.  Previously, [Ru(phen-btL)3][PF6]2 (32) was compared to [Ru(phen)3][PF6]2 (30), and the observed lifetime extension was attributed to excited state equilibration of a bithienyl ligand triplet state (3LCBT) and an intraligand charge transfer state (3ILCT) with the 3MLCT state.158 In the remaining 94  complexes in this study, we observe the bithienyl moieties playing a similar role, albeit not always involving both the 3LCBT and 3ILCT states.  This is illustrated in Figure 3-8, where the TA difference spectra of complexes [Ru(phen-btL)2(dppz)][PF6]2 (50), [Ru(phen- btL)2(tpphz)][PF6]2 (51), and [Ru(phen-btL)2(tatpp)][PF6]2 (52) at t ≈ 1 μs are overlaid.  For 50 and 51, the most notable feature in these spectra is the absence of a MLCT bleach in the 430-480 nm region, indicating that the predominant excited state is not a MLCT-based state but rather a 3LCBT state in equilibrium with a 3MLCTprox state, (as evidenced by emission at ~610 nm).  Comparing emission energies, it is reasonable to suggest that in 50 and 51 the 3MLCTprox state is nearly isoenergetic with the 3LCBT and 3ILCT states observed in [Ru(phen-btL)3][PF6]2 (32), suggesting the BT is playing a similar role in 50 and 51; behaving both as a triplet reservoir, and a reductive quencher for Ru3+.  Figure 3-8. TA difference spectra of 50-52 in CH3CN (t = 0.78 – 1.28 µs, λex = 355 nm, fwhm = 35 ps).   95  Section 3.3.5 – Effect of Zn2+ coordination and solvent environment in unsubstituted tatpp complexes  The TA difference spectrum observed for [Ru(phen-btL)2(tatpp)][PF6]2 (52, Figure 3-8), is essentially identical to that reported for the tatpp 3LC state in [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66).143 However, the excited state lifetime of 52 (in CH3CN) is much longer than that reported for 66 (6 μs vs 0.005 μs). To fully understand the nature of the excited state manifold in triad complexes 50-52 and Zn2+ adducts of [Ru(phen-btL)2(tpphz)][PF6]2 (51Zn) and [Ru(phen- btL)2(tatpp)][PF6]2 (52Zn), it is necessary to first understand the excited state processes in their unsubstituted analogues, [Ru(phen)2(dppz)] 2+ (65), [Ru(phen)2(tpphz)][PF6]2 (53), [Ru(phen)2(tatpp)][PF6]2 (54), and 66.   Figure 3-9. Qualitative Jablonski diagrams of 66 (left) in CH3CN or CH2Cl2 and [Ru(phen)2(tatpp)][PF6]2 (54, right) in CH3CN.  On the left, the red and blue highlights are used to show how the 3MLCTdist is perturbed by the solvent, CH2Cl2 (red) or CH3CN (blue).  On the right, the red and blue highlights are used to show how the 3MLCTdist is perturbed by the presence (blue) or absence (red) of Zn2+.  States in black are less significantly influenced by the solvent or Zn.  Dashed arrows are used to indicate non-radiative decay pathways.  96  The sensitivity of excited state decay processes to solvent is most clearly seen in the ‘light- switch’ behavior reported for [Ru(bpy)2(dppz)] 2+ (70) and [Ru(phen)2(dppz)] 2+ (65) wherein addition of protic solvents to CH3CN solutions switches emission from a ‘bright’ 3MLCTprox state to a ‘dark’ 3MLCTdist state (which is weakly emissive). Conversely, the dark state can be switched to the bright state in an aqueous solution by addition of DNA.  In both cases, the ability of solvent to access and stabilize the excited state dipoles generated is understood to be involved in the light switch behavior.  Because protic solvents can interact with the excited state via protonation or H-bonding in addition to simple dipolar stabilization, their role is not fully understood.164,173 The behavior of [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66) exemplifies how sensitive the MLCT states can be to changes in solvent dipole in the absence of proton donors.  Dinuclear 66 has a Ru2+ ion coordinated to both chelation sites of the tatpp ligand (49) and from electrochemical data it is clear that the energy of the redox orbital is appreciably lower (by approximately 1 eV) than the optical MO.  In this case, it is clear that the 3MLCTdist state is always lower in energy than the 3MLCTprox and that the 3MLCTprox is not noticeably involved in the relaxation process other than as a conduit to the 3MLCTdist or other lower-lying states.  One such lower-lying state is a 3LC state centered on tatpp which is also observed in TA spectra for the Zn(tatpp)Zn4+ (67) adduct (Figure 3-10).  The tatpp ligand is insoluble in most common organic solvents but readily dissolves in CH3CN on addition of Zn 2+.  The non-luminescent 3LCtatpp excited state has a lifetime of τes ≈ 30 μs and the TA spectrum reported for the Zn 2+ adduct is essentially identical to that of 66* in CH2Cl2 at 1 μs. 143  From this and the lifetime data, the Jablonski diagram in Figure 3-9 was proposed by Chiorboli et al.143  Excitation of 66 into absorption bands corresponding to either the 1MLCT state or the 1LC states of the tatpp ligand quickly leads to population of a 3LCtatpp state. 143  In CH2Cl2, the lifetime of this state is 1.3 μs but 97  upon switching to CH3CN, this lifetime drops to τes < 1 ns.  This change in lifetime is due to equilibration between the energetically similar 3LCtatpp and 3MLCTdist states which will exhibit an overall lifetime that is a weighted average of the population of the two individual states (ca. 30 μs for 3LCtatpp and ca. 250 ps for 3MLCTdist 164).  Because a large dipole is induced in the 3MLCTdist state, this state is more stable in polar solvents than in non-polar solvents that influence the ΔE between the two equilibrating states as indicated in Figure 3-9 (left panel).  The shortened lifetime of 66* in more polar solvents reflects a decrease in the ΔE from 0.21 eV in CH2Cl2 to 0.03 eV in CH3CN, as calculated using a two state model. 59  Figure 3-10. Normalized TA difference spectrum of [Ru(phen)2(tatpp)][PF6]2 (54) and ‘Zn(tatpp)Zn’ (67) adduct in CH3CN (λex = 355 nm, fwhm = 35 ps).  Complex [Ru(phen)2(tatpp)][PF6]2 (54) exhibits similar switching behavior to that of 66, except that metalation at the open end may be used to stabilize the energy of the 3MLCTdist state relative to the 3LCtatpp state.  The TA spectrum of 54 reveals that the 3LCtatpp state is also the predominantly occupied state in 54* (Figure 3-10).143 The Jablonski diagram for 54 (Figure 3-9 98  right panel), shows qualitatively similar behavior to 66 but for different reasons.  In this case, the absence of a second Ru2+ center raises the energy of the 3MLCTdist state to 0.18 eV above the 3LCtatpp state in CH3CN, as determined from the lifetimes.  Addition of Zn 2+ shortens the lifetime, from 400 ns to 4 ns, corresponding to a decrease in ΔE from 0.18 eV to 0.06 eV. This is almost the same ΔE as seen for the ruthenium dimer 66 in CH3CN showing that coordination of the Zn2+ ion in 54Zn, in place of the Ru2+ ion, yields nearly identical results.  Section 3.3.6 - Zn2+ coordination and bithiophene effects in tpphz complexes  Figure 3-11. (a) TA difference spectra of [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen)2(tpphz)][PF6]2 (53, t = 551 – 1048 ns); (b) TA difference spectra of [Ru(phen- btL)2(tpphz)][PF6]2 (51Zn) and [Ru(phen)2(tpphz)][PF6]2 (53Zn) in the presence of 5 eq. Zn 2+ (t = 61 – 111 ns). (CH3CN, λex = 355 nm, fwhm = 35 ps) (a) (b) 99   The TA spectra of complexes [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen)2(tpphz)][PF6]2 (53) in CH3CN are overlaid in Figure 3-11a, and those of the corresponding Zn2+ adducts, 51Zn and 53Zn, are shown in Figure 3-11b.  The striking difference between the TA difference spectra of 51 and 53 reveals the significant variation in the nature of their excited states.  In 51, the strong ground state MLCT bleach centered between 400-500 nm indicates that the final excited state resembles a 3MLCT state (where the Ru2+ center has been converted to Ru3+).174 A relatively high energy emission at 604 nm and a moderately long lifetime of 900 ns allows the assignment of the excited state in 53 as a 3MLCTprox excited state.175,176 In 51, the MLCT bleach is not observed, indicating that the predominant excited state species is not a MLCT state (with Ru3+), however the observed emission at 614 nm and extended lifetime of 3.6 μs indicates that the predominant excited state is long-lived and is being depleted via an excited-state equilibration process with the 3MLCTprox state.  Figure 3-12 shows Jablonski diagrams indicating the relevant excited states and their interactions for the Zn2+-adduct and Zn2+-free complexes, 53Zn and 53 (Figure 3-12, left panel), and 51Zn and 51 (Figure 3-12, right panel). In [Ru(phen)2(tpphz)][PF6]2 (53), the 3MLCTprox state is the predominant excited state on the nanosecond timescale.  On the other hand, the adduct 53Zn exhibits luminescence at 660 nm and a shortened lifetime (τes = 90 ns) which are indicative of formation of a 3MLCTdist state, which has been stabilized by Zn2+ coordination.    100   Figure 3-12. Qualitative Jablonski diagrams of [Ru(phen)2(tpphz)][PF6]2 (53, left) in CH3CN and [Ru(phen-btL)2(tpphz)][PF6]2 (51, right) in CH3CN.  In both diagrams, the red and blue highlights are used to show how the 3MLCTdist is perturbed through the addition (blue) or lack (red) of Zn2+. States in black are less significantly influenced by the Zn2+ ion.  The dominant excited state observed in [Ru(phen-btL)2(tpphz)][PF6]2 (51) is a 3LCBT state which is characterized, in part, by absorption in the TA difference spectrum at 420 - 440 nm (Figure 3-12a) and a lifetime enhancement.  The observed emission at 614 nm indicates this 3LCBT state decays via thermal population of a 3MLCTprox state (Figure 3-12, right panel).  In the case of 51, the 3MLCTdist state is higher in energy than the 3MLCTprox state and plays no significant role in the excited-state processes.  As with [Ru(phen)2(tpphz)][PF6]2 (53), coordination of Zn2+ to 51 lowers the energy of the 3MLCTdist state to below that of the 3MLCTprox state as evidenced by emission at 661 nm.  Significantly, the lifetime of adduct 51Zn (τes = 131 ns) is longer than that of 53Zn (τes = 90 ns), and the TA spectra (Figure 3-12b), exhibit similar features, albeit less intense in 51Zn.  One possible reason for this lifetime enhancement could be excited-state equilibration of the 3MLCTdist with a 3ILCT state in which the hole is 101  formally localized on a BT moiety and an electron is localized in the distal tpphz MO.  A clearly observable positive feature is seen at 400 nm in the 51Zn spectrum that is absent in 53Zn and may be attributed to a BT radical cation.109,177 Rapid electron transfer between the neutral BT and an adjacent Ru3+ ion in the 3MLCTdist state would be needed for generation of the aforementioned 3ILCT state. A comparison of ground state redox potentials for Ru2+/3+ and BT0/+ reveals that the two couples are less than 0.1 V apart and that oxidation of the BT moiety by the Ru3+ is exergonic.  Reduction of the distal tpphz orbital, as would be found in the excited state complex 51Zn*, should not alter this situation appreciably.  The potential role of a low-lying 3LCtpphz state being responsible for the enhanced lifetimes can be ruled out, as this should affect both 51Zn and 53Zn equally and the energy of this state is likely to be too high to be involved as the free ligand, tpphz (48), emits at 380 nm (3.15 eV) in CH2Cl2. 171  The light switch behavior of [Ru(bpy)2(tpphz)] 2+ (69) in CH3CN when either protonated with strong acids or metalated (with Ru2+ and Os2+) was first reported by Chiroboli et al.170,178 Similar switching behavior is seen when 69 is bound to DNA in the presence or absence of Zn2+ or Co2+.170 In this latter case, it appears that the DNA bound state essentially approximates the solvent environment of CH3CN. The behavior of 66, [Ru(phen)2(tatpp)][PF6]2 (54), 54Zn, [Ru(phen)2(tpphz)][PF6]2 (53) and 53Zn, as a function of solvent and metalation with Zn 2+ (of which only 53 and 53Zn show actual light switch behavior) reveals that the principal way in which Zn2+ modifies the excited state properties is by modulation of the magnitude of excited state dipole moments, especially with respect to the 3MLCTdist state.  The relative magnitude of the excited state dipoles (μ) in [(phen)2Ru 3+(tpphz▪-)]2+* (53*) would be μ (3MLCTdist) > μ (3MLCTprox).  Equilibration between the 3MLCTprox and 3MLCTdist states is shifted to favor the former in less polar solvents and the latter in solvents of greater polarity.  Upon formation of the 102  53Zn adduct the linear Ru(+3)–tpphz(-1)–Zn(+2) charge configuration in the excited state results in opposed internal dipoles which partially cancel out, resulting in a much smaller excited dipole compared to the Ru(+3)-tpphz(-1) dipole in [Ru(phen)2(tpphz)] 2+* (53*).  In this excited state, the magnitudes of the dipoles are always considerably smaller and the energy of the 3MLCTdist is always lower than that of the 3MLCTprox, regardless of the solvent polarity.  In other words, in 53Zn the charge separated state (3MLCTdist) is the preferred state as the presence of the Zn 2+ at the opposite end of the tpphz ligand results in a Coulombic well that ‘pulls’ the electron towards an orbital in the center of the tpphz ligand.   As discussed below, this is slightly different than the outcome of Zn2+ (or Ru2+) coordination in tatpp complexes 54Zn and 66 where metalation at the open site serves to modulate ΔE between a 3LCtatpp state and the 3MLCTdist state.  The net effect is to stabilize the 3MLCTdist state which would now be the lowest energy state relative to the 3LC state in 66*, resulting in shortening of the excited state lifetime as the equilibrium is shifted to favor the state with the shortest lifetime.   103  Section 3.3.7 - Zn2+ coordination effects and the influence of bithienyl moieties in substituted tatpp complexes   Figure 3-13. (a) TA spectra of the ‘Zn(tatpp)Zn’ (67) adduct (red, t ≈ 1 µs), 52 (blue, t = 456 – 647 ns) and 52Zn (t = 61 – 111 ns); (b) Reductive SEC of 52 (orange, -0.9 V) and TA difference spectra of 52 (blue, t = 456 – 647 ns) and 54 (green, t = 43 – 243 ns). (CH3CN, λex = 355 nm, fwhm = 35 ps)  The TA spectra of complexes ‘Zn(tatpp)Zn’ (67), [Ru(phen-btL)2(tatpp)][PF6]2 (52), and 52Zn in CH3CN are overlaid in Figure 3-13a, and Figure 3-13b shows the TA spectrum of 52 overlaid with [Ru(phen)2(tatpp)][PF6]2 54 (along with the reductive SEC of 52). It is immediately clear that all of the TA spectra resemble the spectrum of the ‘Zn(tatpp)Zn’4+ (67) adduct, and that (a) (b) 104  this spectrum must correspond to the 3LCtatpp state reported by Chiroboli et al. 143 This spectrum features a bleach of the LC transition at 445 nm and three positive features: one feature at higher energy (380 - 420 nm), and two features at lower energies (480 nm and a broad feature between 550 - 650 nm).  Electrochemical reduction (Figure 3-13b, orange trace) of the tatpp ligand in [Ru(phen-btL)2(tatpp)][PF6]2 (52) to form [(phen-btL)2Ru II(tatpp▪-)]+ was observed to bleach the LC transition at 445 nm and give two positive peaks at ~400 and 520 nm, which correspond to a 3MLCTdist state, but also correlate well with two of the three features observed in the 3LCtatpp state.  It appears that the broad low energy peak at 620 nm is a unique characteristic of the LC triplet state.  None of the tatpp complexes are observed to luminesce under any conditions, due to quantitative population of the low-lying 3LCtatpp state regardless of the solvent or metalation state of the complex. In CH3CN, all of the Ru-tatpp complexes have lifetimes on the 1-400 ns timescale, with the notable exception of the BT complex [Ru(phen-btL)2(tatpp)][PF6]2 52 (τes ≈ 6 μs).  A comparison of these data with the TA data for [Ru(phen)2(tatpp)][PF6]2 (54), the previous data for 32, 50, 51, 66, and the associated Zn adducts, illustrates that a triad capable of both vectorial charge transfer and exhibiting a long-lived CS state has been designed and synthesized.  Figure 3-15 shows the qualitative Jablonski diagrams for [Ru(phen-btL)2(tatpp)][PF6]2 (52) and 52Zn derived from an understanding of this data.  This diagram is very similar to that shown for [Ru(phen)2(tatpp)][PF6]2 (54, Figure 3-9, right panel) except for the new states introduced by addition of the BT moieties.  Regardless of the excitation channel, the system undergoes intersystem crossing and relaxation to yield a 3LCtatpp state, as seen from TA data in the sub-500 ns regime (Figure 3-13a).  The lifetime of this state changes from 6 μs without Zn2+ to 100 ns with Zn2+, a 60-fold decrease.  As seen in [Ru(phen)2(tatpp)][PF6]2* (54*), this strong 105  dependence on the presence or absence of Zn2+ is understood within the framework of the 3MLCTdist state accelerating the decay process by depleting the 3LCtatpp state through excited state equilibration.  The energies of the 3MLCTdist states in Zn 2+-free [Ru(phen- btL)2(tatpp)][PF6]2 (52, red) and 52Zn (blue) relative to the 3LCtatpp state are drawn in Figure 3- 14.     Figure 3-14. Qualitative Jablonski diagrams of [Ru(phen-btL)2(tpphz)][PF6]2 (52) and 52Zn in CH3CN.  The red and blue highlights are used to show which states are most perturbed by the presence or absence of Zn2+.  A blue highlight shows the relative energy level of a state in the presence of Zn2+ whereas red shows where the states reside in the absence of Zn2+.  States in black are less significantly influenced by the Zn2+ ion. Dashed arrows are used to indicate non- radiative decay pathways.  Given that the appended BT moieties are spatially far away from the tatpp ligand, it is expected that energies of these states would be similar to those found in [Ru(phen)2(tatpp)][PF6]2 (54, Figure 3-9, right).  In [Ru(phen-btL)2(tatpp)][PF6]2 (52), however, the presence of BT 106  groups extends the lifetime in 52* to 6 μs compared to 450 ns in 54*.  It is very unlikely that the 3MLCTprox or 3LCBT states are involved in lifetime enhancement as they are too high in energy to equilibrate with the 3LCtatpp or 3MLCTdist states.  It is possible that the change from phen in [Ru(phen)2(tatpp)][PF6]2 (54) to phen-btL (28) in [Ru(phen-btL)2(tatpp)][PF6]2 (52) is either raising the energy of the 3MLCTdist or introducing a new low energy 3ILCT state which is now equilibrating with the 3MLCTdist and 3LCtatpp states as drawn in Figure 3-14.   In this new 3ILCT state the hole on Ru3+ in the 3MLCTdist state hops to the BT moiety to form the BT radical cation and the excited state electron is localized in the distal tatpp MO.  Another possibility is one resulting from an increase in the energy of the 3MLCTdist in 52 (and 52Zn) relative to the same state in 54 (and 54Zn).  It is possible that the change from phen to phen-btL (28) alters the Ru2+/3+ oxidation potential such that the energy of the 3MLCTdist state increases relative to the 3LCtatpp state and thereby increases the observed excited state lifetime. Using a two-state model, we can calculate that an increase of 0.072 eV in the energy gap of [Ru(phen-btL)2(tatpp)][PF6]2* (52*) relative to [Ru(phen)2(tatpp)][PF6]2* (54*) would account for the observed increase in lifetime.  This is not an unreasonable increase given that the ground state oxidation potentials for the Ru2+/3+ couple are observed to vary by as much as 50 mV for the compounds in Table 3-1.   However, when the oxidation potentials of the homoleptic complexes [Ru(phen)3][PF6]2 (30) and [Ru(phen-btL)3][PF6]2 (32) are compared, no change is observed.  Similarly, when the Ru2+/3+ oxidation potentials of [Ru(phen-btL)2(tatpp)][PF6]2 (52) and [Ru(phen)2(tatpp)][PF6]2 (54) are compared, only a 40 mV difference is observed, not the 72 mV needed to account for the longer lifetime.  While these data suggest that the perturbation to the energy of the 3MLCTdist in 52* is not enough to account for the observed increase in excited state 107  lifetime, the error associated with measuring these oxidation potentials is significant enough that it is hard to make conclusions based on these data alone.   An additional argument can be made that the increase in Ru2+/3+ oxidation potential in 52Zn should be the same as seen in [Ru(phen-btL)2(tatpp)][PF6]2 (52). It has been previously shown for both [(phen)2Ru(tpphz)Ru(phen)2] 4+ (68) and [(phen)2Ru(tatpp)Ru(phen)2] 4+ (66) that the Ru2+/3+ couples are independent and observed as a single two-electron wave, meaning that the presence of a second metal ion at this remote site does not alter the Ru2+/3+ oxidation potential due to Coulombic effects (it does, however, alter the energy of the tpphz or tatpp reduction potential as expected).  Thus, Zn2+ coordination at the distal site in 52Zn or 54Zn should not alter the Ru2+/3+ potential.  If this is the case, then the Ru2+/3+ oxidation potential in [Ru(phen- btL)2(tatpp)][PF6]2 (52) and 52Zn should be identical and, as such, the increase in the ΔE (3MLCTdist to 3LCtatpp) in 52Zn relative to 54Zn is calculated to give an enhanced lifetime of 69 ns (using the two state model), whereas the observed lifetime is 100 ns.  In this respect, the data are not consistent with a two-state model.  The introduction of a 3ILCT state to give a three equilibrating excited state model is unusual but not unprecedented.65 It is clear from ground state redox data that formation of the 3ILCT state is exergonic from the 3MLCTdist state by as much as 0.1 eV and mechanistically it is easy to rationalize a simple electron-transfer from the BT moiety to the Ru3+ site.  A similar extension of excited state lifetime was seen in tpphz complexes [Ru(phen-btL)2(tpphz)][PF6]2 (51) and 51Zn relative to [Ru(phen)2(tpphz)][PF6]2 (53) and 53Zn due to the presence of BT moieties.  As with the tatpp complexes, this extension could be due to either a change in the Ru2+/3+ oxidation potential or the presence of a 3ILCT state as indicated in Figure 3-14.  While it is not possible to definitively assign the source of the increase in the 108  excited state lifetime of [Ru(phen-btL)2(tatpp)][PF6]2 (52), 52Zn, and 51Zn to the presence of a 3ILCT state, the data support this interpretation.  Section 3.3.8 – The photophysical properties of a directly bound, 2,2’-bipyridine [Ru(phen- btL)2(tatpp)][PF6]2 (52) analog  Chapter 4 outlines some significant differences observed when the linkage binding the thienyl or bithienyl moieties to the chelating ligand is varied. Complimentary to this work, a mononuclear tatpp complex (Chart 3-3, one possible isomer shown) bearing tL (77, Scheme 4-1) ancillary ligands was prepared in the same fashion as [Ru(phen-btL)2(tatpp)][PF6]2 (52).   Chart 3-3.   Contrary to results for [Ru(phen-btL)2(tatpp)][PF6]2 (52), aggregation was not observed in 1H NMR spectra of [Ru(tL)2(tatpp)][PF6]2 (64). Here, it is anticipated that through π-π interactions, this complex may form dimeric species (with Ru2+ centers at opposite ends). Due to the direction in which the thienyl moieties radiate from the metal center, once a dimer is formed, the steric bulk of the thienyl moieties at the ends of the dimeric structure may hinder the approach of other molecules.  109   Figure 3-15. (a) Ground state absorption spectrum of [Ru(tL)2(tatpp)][PF6]2 (64) and (b) transient absorption difference spectrum (shown with decay) of 64 (CH3CN, λex = 355, fwhm = 35 ps).    [Ru(tL)2(tatpp)][PF6]2 (64) was found to be non-emissive, and to exhibit a ground state absorption spectrum (Figure 3-15a) reminiscent of the [Ru(phen-btL)2(tatpp)][PF6]2 (52) analog (Figure 3-4). The excited state difference spectrum of 64 qualitatively appears to be very similar to that recorded for the 52 analog. Moreover, the excited state lifetime of the 2,2'-bipyridyl derivative is much shorter (τes = 48 ns) than that of 52 (τes ≈ 6 μs). This observation highlights the significant role bithienyl moieties play in enhancing the excited state of these complexes. Although the excited state is short lived, the ground state bleach centered at 450 nm fails to relax over the course of the transient absorption experiment. Interestingly, similar behavior was observed in the reductive SEC of this complex (Figure A1-10), suggesting that some photochemistry may be taking place through the excited state manifold. Although the excited state spectrum resembles that of 52, and the ‘Zn(tatpp)Zn’ (67) adduct (determined to be arising from a 3LCtatpp state), the reactivity of the 3MLCT state is clearly preserved in this complex.   (a) (b) 110  Scheme 3-6.  Previously MacDonnell et al. have reported possible dimerization associations that tatpp bridges may undergo in the reduced, and therefore the 3MLCTdist, state. 162 Similar associations have been reported for dppz radical anions, although it is unclear whether the association is π-π stacking in nature, or results in the formation of a covalent σ bond.179,180 The formation of such a dimeric species would account for the lack of recovery in the ground state bleach at 450 nm in the TA experiment:  This bleach is attributed to the formation of a Ru3+ center, and if the electron ejected from the metal center in the 3MLCTdist state is used in creating a bridge from one tatpp to a neighboring one (Scheme 3-6), charge recombination would be prevented, resulting in permanent formation of a Ru3+ center. Additionally, as in the case of the SEC experiment, this region of absorbance in the ground state spectrum is also attributed to transitions on the tatpp bridge; formation of a bridge between two tatpp moieties may also account for a lack of reversibility in this feature. It is unclear as to why photochemical associations or transformations of this type should occur when the ancillary ligand and linkage is varied, but as becomes apparent in Chapter 4, varying the linkage from the phen or bpy to the peripheral thienyl or bithienyl moiety results in specific changes of the excited state structure of these types of complexes.    111  Section 3.4 – Conclusions  The design of triads for light-induced charge separation must address two important factors: the degree or distance of charge separation, and the amount of energy stored in the final CS state.  In [Ru(phen-btL)2(tpphz)][PF6]2 (51), the 3MLCTprox state has approximately the same energy (2.0 eV) as the 3MLCT state in [Ru(phen)3][PF6]2 (30), however in both cases the actual distance over which charge separation occurs is small, as the MLCT state involved has a minimal distance of charge separation (~3 Å, centroid of the phen to the Ru3+ site). In 51Zn, there is a nominal increase in the distance of charge separation to 6.2 Å for the 3MLCTdist state (centroid of the tpphz ligand to the Ru3+ site). The energy of this state can be estimated from the emission data at 1.67 eV.† This correlates well with the energy of this state estimated from the difference in potential between the Ru2+/3+ couple at +1.38 V and the first ligand reduction in [(phen)2Ru(tpphz)Ru(phen)2] 4+ (68) at -0.73 V‡ which gives 1.51 eV.  The energy of the 3ILCT state would be approximately 0.1 eV lower at 1.41 eV but further increases the distance of charge separation to ~11 Å (centroid of the extended BT moiety to the centroid of the tpphz ligand). The excited states in the tatpp complexes are non-luminescent so the energies of the excited states must be estimated using the ground state redox potentials (as was done for 51Zn).  In this case we obtain an excited state energy of ~1.08 eV for the 3MLCTdist state and ~0.98 eV for the 3ILCT state in [Ru(phen-btL)2(tatpp)][PF6]2 (52).  These values drop by ~0.08 eV for the Zn adduct 52Zn but still indicate an appreciable amount of stored energy.  While there is a loss                                                           † While the emission maximum of 661 nm suggests an even higher energy should be possible, previously reported data for the dinuclear ruthenium complex [(phen)2Ru(tpphz)Ru(phen)2] 4+ (68) in CH3CN yields an emission maximum closer to 740 nm giving an energy of the 3MLCTdist state at 1.67 eV, when two metals are bound. Higher energy maxima are seen when ‘mixing’ occurs with mononuclear complex [Ru(phen)2(tpphz)] 2+ (53).168 ‡ Assigned to reduction of the distal or redox MO, at -0.73 V and correcting for intersystem crossing (-0.6 eV taken from the loss observed during intersystem crossing in [Ru(phen)3] 2+*) 112  of 0.5 eV on going from the tpphz to tatpp complexes, the distance of charge separation has increased to ~14 Å (centroid of the BT moiety to the centroid of the tatpp ligand).  If the electron can be transferred via binding of a substrate to the open tatpp site in [Ru(phen-btL)2(tatpp)][PF6]2 (52) or by coordination of the substrate to the Zn2+ in 52Zn, the effective charge separation distance of this transient species would measure over 20 Å.  In light of the discussion in Chapter 1 (Section 1.2), the triads discussed in this chapter satisfy elements 1-4 as dictated by Meyer et al.;5 they undergo light absorption, electron transfer quenching, redox separation by electron transfer and store an appreciable amount of energy to drive catalysis. With further tuning, it may even be possible to initiate multiple electron transfer in these complexes, with two photon excitation, as tatpp has been shown previously to behave as a multielectron storage unit,181,182 further enhancing the utility of these complexes in an artificial photosynthesis system.   113  CHAPTER 4  Elucidating the role of amide linkages in Ru(II) complexes bearing thiophene substituted 2,2’-bipyridine ligands  Section 4.1 – Introduction  In recent years, a number of studies have been reported featuring integrated amide-linkage motifs with a broad range of functions and applications. Whitesides and coworkers have shown that switching from a saturated –CH2CH2– linkage to a more polar –C(O)NH– linkage in the self-assembled monolayer component of junctions comprised of AgTS-SAM//Ga2O3/EGaIn does not result in a dramatic variation in charge transfer by tunneling, although incorporation of the amide linkage does result in an increase in the number of working junctions.183 In fullerene-peptide-radical systems, Turro et al. have shown that the directionality of the peptide-bridge plays a significant role in controlling the physiochemical properties of the system. Through the formation of helices possessing an aspect of directionality, the redox and optical properties of these robust systems are altered, as the dipole moment of the peptide bridge varies.184  Figure 4-1. A chromophore-amide-catalyst dyad reported by Meyer et al.185 114   Meyer et al. have investigated photoinduced electron transfer in a number of chromophore- catalyst dyads anchored to semiconductor surfaces (such as TiO2). In a recent report (Figure 4.1), Meyer and coworkers have suggested that incorporating a benzamide linkage (71) results in the formation of a saturated linker between the chromophore and catalyst, allowing both components to retain their original optical properties.185,186 In the study by Meyer et al., inclusion of a saturated amide linkage provides a platform for controlling electronic coupling and intramolecular electron transfer rates, combined with ease of synthetic modification. In previous sections of this thesis, a number of metal complexes incorporating amide- linked thiophene and oligothiophene ligands have been described. These systems often exhibit multicomponent excited state manifolds with several equilibrating excited state species present. The role of the amide linkage in these complexes is not well understood, and based on these studies it is unclear whether the amide linkage plays an active role in electron and/or energy transfer processes, or if it merely behaves as a synthetically accessible linker with minimal influence on the electronic structure of the final complex. To probe this question a number of Ru2+ complexes incorporating thienyl moieties through 2,2'-bipyridine ligands have been prepared (Section 4.3.1). Previously, Swager et al. have reported Ru2+ complexes (72, 73) with 4,4'- and 5,5'- substituted 2,2'-bipyridine ligands (Chart 4-1). These positions were substituted with directly bound bithiophene groups resulting in the formation of complexes that readily undergo electropolymerization. The photophysical properties of these complexes, however, have not been explored.93,187 These complexes in which the bithiophene is directly attached to the bipyridine ligand can be compared to their amide bound analogs in order to provide a comparison of how the photophysical properties depend on the link between components.  Additionally, it has been 115  shown that substitution at the 4,4'- positions versus the 5,5'- positions results in the greatest degree of conjugation, or electronic communication between the peripheral substituents and the metal center.93,187,188  As a result, this substitution pattern is used here to probe the effects of varying the linkage between peripheral thienyl moieties and the metal center. Chart 4-1. Ref. 93,187  Comparison of emission, ground state absorption properties and transient absorption spectroscopy (TA) of complexes with both directly and amide-linked peripheral thienyl groups (Section 4.3.1) offers insight into the role of the amide linkage. Several possible scenarios can be envisioned: the amide linkage may act like a saturated linker resulting in weak or no electronic coupling between the metal center and the substituents; through-bond electron transfer (superexchange) may occur by way of the partial double-bond character of the amide linkage;189 the amide linkage may simply bring the substituents into close proximity with the metal center allowing for through-space electron and energy transfer; or in the simplest case, the amide linkage may behave (depending on the connectivity) as an electron donating or electron withdrawing group,190-192 influencing the band gap of the excited state. A primary consideration in determining which of these scenarios shape the excited state is determination of which ligand, in the case of a heteroleptic ML2L' complex, is behaving as the electron acceptor. 116   Section 4.2 – Experimental  Section 4.2.1 – General  2,2'-Bipyridine and NH4PF6 (Alfa), thiophene-2-boronic acid, tetrathiafulvalene, methyl viologen dichloride (Sigma), Pd(PPh3)4 and RuCl3·xH2O (Strem), were purchased from commercial sources and used as received. [2,2'-Bithiophen]-5-yltri-tert-butylstannane used in the preparation of btL (78) was synthesized by Dr. Agostino Pietrangelo.193 Anhydrous THF was obtained via distillation from Na/benzophenone, and anhydrous CH2Cl2 was obtained via distillation from CaH. All other solvents were used as received. Silica gel used in purification was purchased from Silicycle (SiliaFlash F60 or G60). Heterocyclic precursors 2,2'-bipyridine-N,N'-dioxide (74),194 4,4'-dinitro-2,2'-bipyridine- N,N'-dioxide (75),195 4,4'-dibromo-2,2'-bipyridine (76) 196 and 4,4'-diamino-2,2'-bipyridine (79),195 were all prepared as previously reported. These intermediates were isolated and characterized by comparison to the reported literature characterization. In all cases, with the exception of 4,4'-dibromo-2,2'-bipyridine (76), the methods and resulting yields agreed closely with those reported in literature. Initially, preparation of 4,4'-dibromo-2,2'-bipyrdine (76) from 4,4'-dinitro-2,2'-bipyridine-N,N'-dioxide (75) was attempted with PBr3 in anhydrous CH2Cl2 followed by neutralization with 25% NaOH. Unfortunately, this synthetic route proved to be extremely low yielding, and so the method proposed by Cid et al. was utilized. The crude product (82% crude yield) from this method was purified by column chromatography (47:47:6 Hex:EtOAc:MeOH). Metal-containing precursor Ru(bpy)2Cl2 (80) was also prepared according to published procedures.148 Ru(tL)2Cl2 (81) and Ru(sec-amL)2Cl2 (82) were prepared using a slightly 117  modified procedure where Ru(DMSO)4Cl2 (prepared as in ref. 96) was combined with 2 equivalents of the desired ligand in EtOH or EtOH/H2O, and in the presence of LiCl. The resulting precipitates were collected, the expected structure was confirmed by MALDI-TOF MS, and used in the following reactions without further characterization or purification due to poor solubility and instability of the complexes to recrystallization.149 [Ru(bpy)3][PF6]2 (1) was prepared by addition of a saturated NH4PF6(aq) solution to an aqueous solution of [Ru(bpy)3]Cl2 (Strem). The resulting bright orange precipitate was collected by filtration and used without any further purification. 1H and 13C NMR spectra were obtained on either a Bruker AV-300, Bruker AV-400Direct or Bruker AV-400Indirect spectrometer. All chemical shifts in 1H and 13C spectra were referenced to residual solvent, and the splitting patterns are designated as s (singlet), d (doublet), t (triplet), m (multiplet) or br (broad). NMR solvents (Cambridge Isotope Laboratories or Sigma) were used as received.  ESI MS (Waters ZQ with ESCI ion source) and HR-ESI MS (Bruker Esquire LC-MS) were obtained at the UBC Microanalysis facility. Samples for spectroscopic measurements were prepared using HPLC-grade Fisher solvents. Electronic absorption spectra were recorded on a Varian-Cary 5000 UV-Vis-near-IR spectrophotometer.  Emission spectra and quantum yield measurements were recorded on a Photon Technology International QuantaMaster 50 fluorimeter fitted with an integrating sphere, double monochromator and utilizing a 75W Xe arc lamp as the source. Transient absorption excited state spectra and lifetimes were collected using methods described in Section 2.2.2.    118  Section 4.2.2 – Methods  4,4'-di(thiophen-2-yl)-2,2'-bipyridine (77, tL)  THF (10 mL), 4,4'-dibromo-2,2'-bipyridine 76 (151 mg, 0.481 mmol), thiophene-2-boronic acid (123 mg, 0.961 mmol) were placed into a round bottom flask, under N2. The mixture was further purged with N2 for 20 minutes, after which aqueous 2M Na2CO3 (1 mL) was added. The biphasic reaction mixture was purged with N2 for a further 5-10 minutes. Subsequently, Pd(PPh3)4 (3% mol, 17 mg) was added and the mixture was heated to 90°C. The reaction progress was monitored by TLC (8:2 Hex:EtOAc) and after 20 hours, 4,4'-dibromo-2,2'- bipyridine (76) was no longer observed. A spot near the baseline of the TLC plate was observed, and attributed to a mono-substituted product, so an additional portion of thiophene-2-boronic acid (23 mg, 0.18 mmol) was added to the reaction mixture. After 27 hours of total reaction time, the reaction was deemed to have reached completion by TLC (8:2 Hex:EtOAc and 98:2 CHCl3:MeOH), and was cooled to room temperature.  THF was removed from the reaction mixture under reduced pressure, and the residue was dissolved in CH2Cl2 then washed with water (3 × 10 mL) to remove any residual salts. The organic layer was separated and dried over anhydrous Na2SO4, then concentrated under reduced pressure. The concentrated mixture was passed through a silica gel plug on a frit with 98:2 CHCl3:MeOH eluent. The collected washings were combined, and the solvent was removed under reduced pressure to yield a grey solid; the title compound. Yield: 75 mg (66 %). 1H NMR (400 MHz, CDCl3) δ ppm 7.16 (dd, J=4.95, 3.58 Hz, 1H), 7.44 (dd, J=5.12, 1.02 Hz, 1H), 7.53 (dd, J=5.12, 1.71 Hz, 1H), 7.67 (dd, J=3.75, 1.02 Hz, 1H), 8.66 – 8.71 (m, 2H).  13C (100.63 MHz, CDCl3) δ ppm 117.07, 119.73, 125.39, 126.91, 128.07, 141.07, 142.17, 149.34, 156.09. ESI MS m/z 321.2 ([M + H]+). 119  4,4'-di([2,2'-bithiophen]-5-yl)-2,2'-bipyridine (78, btL)  4,4'-Dibromo-2,2'-bipyridine 76 (150 mg, 0.478 mmol) and 2.5 equivalents of [2,2'- bithiophen]-5-yltri-tert-butylstannane (546 mg, 0.45 mL, 1.20 mmol) were added to 50 mL anhydrous toluene under N2. The solution was purged with N2 for 20 minutes, after which 3% mol of Pd(PPh3)4 (27 mg, 0.02 mmol) was added. The mixture was heated at 100°C for 3 days; during this time, the reaction was monitored by TLC (98:2 CHCl3:MeOH). The reaction mixture was then filtered to remove any insoluble solids that had formed, concentrated under reduced pressure, and dissolved in 50 mL of anhydrous toluene with the addition of another 1 equivalent (0.48 mmol) of [2,2'-bithiophen]-5-yltri-tert-butylstannane and an additional 3% mol of Pd(PPh3)4. After an additional 24 hrs heating at reflux, TLC analysis of the reaction mixture showed no starting material remained. The reaction mixture was cooled to room temperature and reduced in volume to approximately 3 mL under reduced pressure and left at 4°C overnight, resulting in the formation a yellow/orange precipitate, the title compound previously reported in literature.93 1H NMR (400 MHz, CDCl3) δ ppm 7.04 - 7.09 (m, 1 H) 7.12 (d, J=3.35 Hz, 1 H) 7.23 (d, J=3.35 Hz, 1 H) 7.27 - 7.31 (m, 1 H) 7.51 (d, J=3.65 Hz, 1 H) 7.58 (d, J=3.35 Hz, 1 H) 8.65 (br. s., 1 H) 8.69 (d, J=3.96 Hz, 1 H). 13C (100.63 MHz, CDCl3) δ ppm 117.23, 119.85, 124.68, 125.06, 125.47, 126.74, 128.34, 136.58, 137.19, 139.60, 150.07, 156.80. ESI MS m/z 485.1 ([M + H]+).  N,N'-([2,2'-bipyridine]-4,4'-diyl)bis(thiophene-2-carboxamide) (83, sec-amL)  Thiophene-2-carboxylic acid 35 (120 mg, 0.939 mmol) was added to 5 mL anhydrous CH2Cl2. The mixture was cooled to 0°C, and SOCl2 (0.2 mL, 2.818 mmol) was added drop-wise followed by 2 drops of DMF. This reaction mixture was warmed to room temperature and then 120  heated to reflux for 1 hour. After 1 hour, the solvent was removed under reduced pressure and the residue (thiophene-2-carbonyl chloride, 35Cl) was used in the next step without further purification or characterization. 4,4'-Diamino-2,2'-bipyridine 76 (159 mg, 0.854 mmol) was dissolved in 40 mL of anhydrous THF, along with Hunig’s base (0.7 mL). This mixture was added to the acyl chloride residue collected above, which had been cooled to 0°C. A substantial amount of white vapor formed (presumed to be HCl(g)), and was removed from the reaction vessel with a steady stream of N2. The reaction was allowed to warm to room temperature, and then heated to reflux overnight under N2. After heating, the solvent was removed under reduced pressure, yielding a brown oily residue. On addition of H2O to this residue, a white solid formed and was collected by filtration. This white solid was recrystallized from MeOH/H2O to yield the title compound. Yield 139 mg (40%). 1H NMR (400 MHz, DMSO-d6) δ ppm 7.27 (dd, J=5.12, 3.75 Hz, 1H), 7.94 (dd, J=4.95, 1.19 Hz, 1H), 7.98 (dd, J=5.46, 2.05 Hz, 1H), 8.17 (dd, J=3.76, 1.02 Hz, 1H), 8.60 (d, J=5.46 Hz, 1H), 8.77 (d, J=2.05, 1H), 10.71 (s, 1H, N-H). 13C (100.63 MHz, CDCl3) δ ppm 111.39, 114.70, 128.96, 130.76, 133.67, 139.78, 147.43, 150.66, 156.59, 161.30. ESI MS m/z 407.3 ([M + H]+).  N,N'-([2,2'-bipyridine]-4,4'-diyl)bis(N-ethylthiophene-2-carboxamide) (84, tert-amL)  Crushed KOH (224 mg, 3.99 mmol) was added to DMSO (2 mL). After 5 minutes of stirring this suspension, 83 (63 mg, 0.155 mmol) was added, followed by CH3CH2I (0.33 mL, 4.0 mmol). The resulting suspension was stirred for 30 minutes and then poured into 10 mL of a 1:1 MeOH:H2O mixture. This mixture was left at 4°C for 2 days, resulting in the formation of a small quantity of white powder (the title compound) that was collected by filtration. Yield: 10 121  mg (14%).  1H NMR (300 MHz, DMSO-d6) δ ppm 1.14 (t, J=7.08 Hz, 3H), 3.94 (q, J=7.16 Hz, 2H), 6.92 (d, J=3.43 Hz, 2H), 7.40 (dd, J=5.25, 2.28 Hz, 1H), 7.67 – 7.71 (m, 1H), 8.25 (d, J=1.83 Hz, 1H), 8.65 (d, J=5.25 Hz, 1H). ESI MS m/z 485.1 ([M + Na]+).  General procedure for preparation of heteroleptic Ru2+ complexes  Ru(bpy)2Cl2 (80) and 1.1 equivalents of the desired ligand were suspended in a mixture of 1:1 EtOH:H2O (20 mL) and purged for 30 mins with N2. The mixture was heated to reflux under N2, and left heating at this temperature overnight. After heating, the bright orange to deep red solution was filtered hot through glass wool to remove any insoluble impurities, and treated with a minimal amount (ca. 2 mL) of a saturated solution of NH4PF6(aq). The resulting dark orange precipitate was collected by vacuum filtration, washed with small amounts (2 – 5 mL) of H2O and EtOH and left to air dry. This crude product was further purified by column chromatography. The product was dissolved in a small volume of CH3CN and eluted through a silica gel column using a 96:3:1 CH3CN:H2O:KNO3(aq) solvent mixture. The major orange band (a NO3 - salt of the target complex) was collected, and the solvent was removed under reduced pressure. The residue was dissolved in a small volume of MeOH, passed through glass wool (to remove insoluble KNO3) into an aqueous saturated solution of NH4PF6. The resulting precipitate was collected by vacuum filtration, washed with small portions (2 mL) of H2O, EtOH and Et2O (sequentially) and left to air dry.  X-ray quality crystals of these complexes were subsequently obtained by preparation of a saturated solution in CH2Cl2 or CH3CN, and layering this solution with a small volume of Et2O.  122  [Ru(bpy)2(tL)][PF6]2 (85)  Yield: 30 mg (37%). 1H NMR (400 MHz, CD3CN) δ ppm 7.29 (dd, J=4.78, 3.76 Hz, 1H) 7.38 - 7.45 (m, 2H) 7.56 (dd, J=5.80, 2.05 Hz, 1H) 7.66 (d, J=5.80 Hz, 1H) 7.73 (ddd, J=9.81, 5.38, 0.85 Hz, 2H) 7.86 (dd, J=5.80, 0.68 Hz, 1H) 7.96 (dd, J=3.76, 1.02 Hz, 1H) 8.07 (td, J=8.02, 1.02 Hz, 2H) 8.51 (d, J=8.19 Hz, 2H) 8.77 (d, J=1.71 Hz, 1H). 13C (100.63 MHz, CD3CN) δ ppm 118.40, 121.45, 124.53, 125.62, 128.98, 129.95, 130.70, 131.64, 139.19, 140.18, 153.04, 158.34, 158.62. HR-ESI MS m/z [M]+ calcd for C38H28N6F6PS2Ru, 873.0524; found, 873.0535 (-1.3 ppm).  [Ru(bpy)2(btL)][PF6]2 (86)  The entire product from the synthetic procedure was used in preparing a crystallographic sample, characterization, and performing spectroscopic measurements. No yield was calculated. 1H NMR (400 MHz, CD3CN) δ ppm 7.14 (dd, J=5.18, 3.65 Hz, 1H) 7.37 - 7.45 (m, 5H) 7.46 - 7.55 (m, 2H) 7.65 (d, J=6.09 Hz, 1H) 7.74 (d, J=4.87 Hz, 1H) 7.84 - 7.88 (m, 1H) 7.92 (d, J=3.96 Hz, 1H) 8.07 (td, J=7.92, 1.52 Hz, 3H) 8.51 (d, J=8.53 Hz, 3H) 8.74 (d, J=1.83 Hz, 1H). HR-ESI MS m/z [M]+ calcd for C46H32N6F6PS4Ru, 1040.0247; found, 1040.0273 (-2.5 ppm).  [Ru(bpy)2(sec-amL)][PF6]2 (87)  The crude product was purified by silica gel chromatography using 50:6:2 CH3CN:H2O:KNO3(aq) as the eluent. Yield: 62 mg (27%).  1H NMR (400 MHz, CD3CN) δ ppm 7.23 (dd, J=4.95, 3.93 Hz, 1H), 7.36 – 7.48 (m, 2H), 7.54 (d, J=6.49 Hz, 1H), 7.66 (dd, J=6.32, 2.22 Hz, 1H), 7.72 – 7.82 (m, 2H), 7.87 – 7.96 (m, 2H), 8.05 (tdd, J=7.89, 7.89, 5.03, 1.37 Hz, 123  2H), 8.46 – 8.54 (m, 2H), 9.03 (d, J=2.39 Hz, 1H), 9.49 (s, 1H). 13C (100.63 MHz, CD3CN) δ ppm 114.71, 118.28, 125.52, 128.82, 128.90, 129.91, 131.63, 134.89, 138.90, 139.75, 148.79, 153.07, 153.15, 158.44, 158.57, 158.76, 162.58. HR-ESI MS m/z [M]+ calcd for C40H30N8F6PO2S2Ru, 962.0641; found, 962.0634 (0.7 ppm).  [Ru(bpy)2(tert-amL)][PF6]2 (88)  Yield: 5 mg (24%). 1H NMR (400 MHz, CD3CN) δ ppm 1.21 (t, J=7.17 Hz, 3H) 4.01 (qd, J=7.11, 1.88 Hz, 2H) 6.84 (dd, J=4.95, 3.93 Hz, 1H) 6.91 (dd, J=3.76, 1.02 Hz, 1H) 7.20 (dd, J=6.14, 2.39 Hz, 1H) 7.38 (ddd, J=7.42, 5.89, 1.37 Hz, 1H) 7.51 - 7.54 (m, 1H) 7.56 (d, J=6.14 Hz, 1H) 7.73 (d, J=5.80 Hz, 1H) 7.77 (d, J=5.46 Hz, 1H) 8.05 (dd, J=15.70, 1.37 Hz, 1H) 8.11 - 8.16 (m, 2H) 8.50 (t, J=8.19 Hz, 3H). HR-ESI MS m/z [M]+ calcd for C44H38N8O2F6PS2Ru, 1018.1259; found, 1018.1260 (-0.1 ppm).  [Ru(tL)3][PF6]2 (89)  Ru(tL)2Cl2 81 (68 mg, 0.080 mmol) and an excess of 77 (40 mg, 0.12 mmol) were suspended in 10 mL of 4:1 EtOH:H2O which had been purged for 30 minutes with N2. The mixture was heated to reflux and left at that temperature for 24 hours. The mixture was then centrifuged to remove any insoluble impurities, and the supernatant was decanted. This dark red solution was filtered through glass wool into a saturated aqueous solution of NH4PF6 to yield a deep red precipitate that was collected by vacuum filtration. The solid collected from centrifugation was suspended in 10 mL of 4:1 EtOH:H2O and heated to reflux overnight after the addition of a second portion of 77 (20 mg, 0.062 mmol). The same work up as above was 124  performed, and a second portion of deep red product was collected. The two products were combined and chromatographed on silica gel with a 96:3:1 CH3CN:H2O:KNO3(aq) eluent. The major dark red band was collected, concentrated under reduced pressure and treated with a solution of NH4PF6(aq) to yield the desired product. Yield: 39 mg (36 %).  1H NMR (400 MHz, (CD3)2CO) δ ppm 7.32 (dd, J=5.03, 3.81 Hz, 2H) 7.79 (dd, J=6.09, 1.83 Hz, 2H) 7.84 (dd, J=5.03, 0.76 Hz, 2H) 8.04 (dd, J=3.65, 0.91 Hz, 2H) 8.19 (d, J=6.09 Hz, 2H) 9.24 (d, J=1.83 Hz, 2H). 13C (150.91 MHz, (CD3)2CO) δ ppm 121.29, 124.69, 129.99, 130.64, 131.67, 140.14, 144.32, 153.30, 158.97. HR-ESI MS m/z [M]+ calcd for C54H36N6F6PS6Ru, 1204.0044; found, 1204.0027 (1.4 ppm).  [Ru(sec-amL)3][PF6]2 (90)  Ru(sec-amL)2Cl2 82 (47.2 mg, 0.0509 mmol) and sec-amL 83 (20.7 mg, 0.0509 mmol) were suspended in 10 mL of 4:1 EtOH:H2O, purged with N2, and heated to reflux. The mixture was heated to reflux overnight, and during this time the chloride salt of the desired product precipitated from the solution. [Ru(sec-amL)3]Cl2 was collected by vacuum filtration, and then dissolved in 1:1 THF:MeOH with heating. This solution was treated with a saturated solution of NH4PF6(aq), and the mixture concentrated under reduced pressure resulting in the formation of title compound as a dark orange precipitate. This precipitate was suspended in a small volume of H2O and filtered. This precipitate was eluted through a basic alumina column using acetone. The major orange band was collected, the solvent removed under reduced pressure. The resulting residue was treated with a saturated NH4PF6(aq) solution to yield the title complex as a dark orange precipitate. Yield 25 mg (30%).  1H NMR (400 MHz, CD3CN) δ ppm 7.24 (dd, J=5.03, 3.81 Hz, 2H), 7.68 – 7.74 (m, 4H), 7.81 (d, J=4.87 Hz, 2H), 7.93 (d, J=3.65 Hz, 2H), 9.04 (d, 125  J=1.52 Hz, 2H), 9.39 (s, 2H).  13C (100.63 MHz, CD3CN) δ ppm 114.65, 118.23, 129.92, 131.58, 134.89, 139.80, 148.39, 153.31, 159.08, 162.57. HR-ESI MS m/z [M]+ calcd for C60H41N12O6S6Ru, 1316.0685; found, 1316.0656 (2.2 ppm).  Section 4.2.3 - X-Ray crystallography  The crystal structures of [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(btL)][PF6]2 (86), [Ru(bpy)2(sec-amL)][PF6]2 (87), [Ru(bpy)2(tert-amL)][PF6]2 (88) were obtained by Dr. B. O. Patrick at UBC. All measurements were made on a Bruker APEX DUO diffractometer with graphite monochromated Mo-Kα radiation. Data were collected and integrated using the Bruker SAINT197 software package. Data were corrected for absorption effects using the multi-scan technique (SADABS or TWINABS198). The data were corrected for Lorentz and polarization effects. The structures were solved by direct methods.199  Diagrams were drawn using CCDC Mercury 3.0.200  [Ru(bpy)2(tL)][PF6]2 (85)  A red irregular crystal of C38H28N6RuS2P2F12▪1.5CH2Cl2, having approximate dimensions of 0.10 × 0.22 × 0.75 mm was mounted on a glass fiber. The data were collected at a temperature of -183.0 + 0.1°C to a maximum 2ϴ value of 55.8°. Data were collected in a series of  and ω scans in 0.5° oscillations using 8.0-second exposures. The crystal-to-detector distance was 59.88 mm. The material crystallizes as a multi-component twin, however the major component is significantly larger than any other components.  As there was no significant overlap between the different components the HKLF4 data were used for all structure solution and refinement.  Of the 126  47661 reflections that were collected, 10188 were unique (Rint = 0.040); equivalent reflections were merged.  The material crystallizes with 1.5 molecules of CH2Cl2 in the asymmetric unit, one of which is disordered in two orientations.  Additionally, one thiophene ring (containing S1) is disordered in two orientations.  Finally, one PF6 anion is disordered and was modeled in two orientations.  All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated positions.  The final cycle of full-matrix least-squares refinement on F2 was based on 10188 reflections and 720 variable parameters and converged. All refinements were performed using the SHELXL-97201 via the WinGX202 interface.  [Ru(bpy)2(btL)][PF6]2 (86)  A red plate crystal of C46H32N6S4Ru.2PF6▪2CH2Cl2 having approximate dimensions of 0.04 × 0.24 × 0.36 mm was mounted on a glass fiber. The data were collected at a temperature of -183.0 + 0.1oC to a maximum 2ϴ value of 50.5o. Data were collected in a series of  and ω scans in 0.5o oscillations using 20.0-second exposures. The crystal-to-detector distance was 50.02 mm. The material crystallizes as a two-component twin with components one and two related by a 180.0º rotation about the (0 0 1) real axis.  Data were integrated for both twin components, including both overlapped and non-overlapped reflections.  In total 42110 reflections were integrated (5690 from component one only, 4924 from component two only, 31496 overlapped).   The structure was solved by direct methods199 using non-overlapped data from the major twin component.  Subsequent refinements were carried out using an HKLF5 format data set containing complete data from component one and overlapped reflections from component two.  127  Both terminal thiophene groups are disordered by rotation about C – C single bonds.  A series of SAME/EADP/SADI commands were used to ensure reasonable geometries and displacement parameters.  A list of the constraints and restraints used in this refinement can be found within the CIF.  Finally, the material crystalizes with two methylene chloride solvent molecules in the asymmetric unit.  All non-hydrogen atoms were refined anisotropically.  All hydrogen atoms were placed in calculated positions.  The final cycle of full-matrix least-squares refinement on F2 was based on 9544 reflections and 739 variable parameters and converged. All refinements were performed using the SHELXL-97201 via the WinGX202 interface.  [Ru(bpy)2(sec-amL)][PF6]2 (87)  A red prism crystal of C40H30N8O2F12P2S2Ru▪2CH3CN having approximate dimensions of 0.08 × 0.10 × 0.19 mm was mounted on a glass fiber. The data were collected at a temperature of -183.0 + 0.1°C to a maximum 2ϴ value of 50.9°. Data were collected in a series of  and ω scans in 0.5° oscillations using 30.0-second exposures. The crystal-to-detector distance was 40.19 mm. The material crystallizes as a two-component ‘split-crystal’ with components one and two related by a 179.2° rotation about the (0.147 1 0.090) real axis.  Data were integrated for both twin components, including both overlapped and non-overlapped reflections.  In total 62120 reflections were integrated (31517 from component one only, 27954 from component two only, 2649 overlapped).  The structure was solved by direct methods199 using non-overlapped data from the major twin component.  Subsequent refinements were carried out using an HKLF4 format data set containing complete data from component one.  Both PF6 anions are disordered in two orientations by rotation about a F—P—F axis.  A series of SADI commands were used to ensure 128  reasonable geometries and displacement parameters.  A list of the constraints and restraints used in this refinement can be found within the CIF.  All non-hydrogen atoms were refined anisotropically.  H2N and H4N were located in difference maps and refined isotropically.  All other hydrogen atoms were placed in calculated positions.  The material crystallizes with significant amounts of solvent acetonitrile in the lattice.  Two such molecules were modeled, however there is a region within the unit cell where the remaining CH3CN molecules are disordered and could not be reasonably modeled.  As a result the PLATON/SQUEEZE203 program was employed to generate a ‘solvent-free’ data set.  Ultimately the equivalent of 160 electrons were removed from the void space in the lattice, an amount consistent with something between 3 and 4 acetonitrile solvent molecules in the asymmetric unit. The empirical formula contains only those solvent molecules that were refined in the structure, not those removed via SQUEEZE.  The final cycle of full-matrix least-squares refinement on F2 was based on 10593 reflections and 740 variable parameters and converged. All refinements were performed using the SHELXL-2012201 via the Olex2204 interface.  [Ru(bpy)2(tert-amL)][PF6]2 (88)  A red plate crystal of C44H38N8O2RuS2P2F12▪CH2Cl2, having approximate dimensions of 0.02 × 0.09 × 0.24 mm was mounted on a glass fiber. The data were collected at a temperature of -183.0 + 0.1°C to a maximum 2ϴ value of 50.2°. Data were collected in a series of  and ω scans in 0.5° oscillations using 45.0-second exposures. The crystal-to-detector distance was 39.97 mm. Of the 43504 reflections that were collected, 9064 were unique (Rint = 0.065); equivalent reflections were merged. The material crystallizes with one molecule of CH2Cl2 in the asymmetric unit.  Additionally, one thiophene ring (containing S2) is disordered in two 129  orientations by 180° rotation about the C16 – C17 bond.  Finally, there is one PF6 anion located in a general position.  The second anion is located on two special positions, with one half-anion residing on a two-fold rotation axis.  All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in calculated positions.  The final cycle of full-matrix least-squares refinement on F2 was based on 9064 reflections and 695 variable parameters and converged. All refinements were performed using the SHELXL-97201 via the WinGX202 interface.  Section 4.3 - Results and discussion  Section 4.3.1 - Synthesis and characterization  The series of symmetrical ligands (77, 78, 83 and 84) described in this chapter was prepared using modifications of previously reported procedures. Ligand tL (77) was prepared via Suzuki coupling of 4,4'-dibromo-2,2'-bipyridine with thiophene-2-boronic acid in the presence of catalytic amounts of Pd(PPh3)4. A bithienyl analog of 77, btL (78) was prepared by a modified Stille coupling reported by Swager et al.93,187 The structure of the desired ligand, btL (78), was confirmed by NMR and mass spectrometry, albeit with some impurity present. It proved challenging to obtain a pure sample of this ligand using this method, and the impure product was used in the preparation of the corresponding heteroleptic complex. Any residual impurities (largely containing -Sn(t-Bu)3 fragments) were removed from the Ru 2+ complex via column chromatography.    130  Scheme 4-1.    The precursor to these ligands, 4,4'-dibromo-2,2'-bipyridine (76), was prepared using a step-wise procedure. First, 2,2'-bipyridine was converted to the N,N'-oxide analog (74) using H2O2 as an oxidant, followed by nitration at the 4 and 4' positions (75). The resulting N,N'- dioxide-4,4'-dinitro-2,2'-bipyridine (75) was converted into the target molecule via reduction of the N-oxide groups, and subsequent ipso-carbon substitution with acetyl bromide. Loss of the N,N'-dioxide groups was confirmed through the disappearance of ν[N-O] IR bands (1263 cm-1). The product was purified via column chromatography to yield pure 4,4'-dibromo-2,2'-bipyridine (76), as evidenced by comparison of 1H NMR spectroscopy and mass spectrometry characterization data to literature values. This synthetic pathway proved relatively low yielding, however no suitable alternative was found. 131  Ligand sec-amL (83) was prepared using a modified previously discussed procedure (Section 2.2.3), where the thiophene-2-carboxylic acid chloride was reacted with 4,4'-diamino- 2,2'-bipyridine (79). The precursor 4,4'-diamino-2,2'-bipyridine (79) was prepared using a known literature procedure,195 via 10% Pd/C catalyzed reduction of the 4,4'-dinitro (75) derivative prepared as described above in the presence of N2H2. Thiophene-2-carboxylic acid chloride (35Cl) was prepared through reaction with SOCl2 in the presence of a catalytic amount of DMF, followed by removal of solvent and unreacted SOCl2 under reduced pressure. The acyl chloride derivative (35Cl) was used as prepared in a reaction with 4,4'-diamino-2,2'-bipyridine (79), without any further purification or characterization. Scheme 4-2.   The sec-amL (83) ligand was converted to the tert-amL (84) analog via deprotonation of the amide by solid KOH in DMSO, followed by reaction with CH3CH2I. 205 Conversion to the tert-amL (84) analog was monitored using 1H NMR spectroscopy, where loss of the diagnostic 132  amide hydrogen resonance (δ 10.71 ppm) was recorded after reaction with KOH. On reaction with CH3CH2I, resonances attributed to the newly installed ethyl group were observed (δ 1.14 ppm, δ 3.93 ppm). The identity of the final product was confirmed by 1H NMR spectroscopy and mass spectrometry and the compound was used without further purification in the preparation of [Ru(bpy)2(tert-amL)][PF6]2 (88). The installation of an ethyl group at the amide –N atom has been previously shown to result in a ‘twisted’ amide conformation,189,206,207 however no evidence for this behavior was observed in the NMR spectra of this ligand.  Scheme 4-3.  Heteroleptic Ru2+ complexes of all the ligands were prepared by reaction of cis- Ru(bpy)2Cl2 (80) with the desired ligand in EtOH/H2O (Scheme 4-3). The target complexes were isolated as hexafluorophosphate salts by addition of a saturated aqueous NH4PF6 solution resulting in formation of precipitates orange, red or dark red in color. These precipitates were purified by column chromatography with CH3CN/H2O/KNO3(aq) as eluent and the final products were characterized using 1H and 13C NMR spectroscopy, high resolution mass spectrometry and various ground and excited stated spectroscopic methods.  133  Although Δ- and Λ- isomers of these heteroleptic complexes are possible, no efforts were made to isolate the isomers. For convenience, the metal complexes are all drawn as Λ- isomers. 1H and 13C NMR spectra were consistent with symmetrical species in solution, confirming the expected C2 symmetry of these ML2L' type complexes. 93  Section 4.3.2 - Solid state characterization  X-ray quality crystals of complexes 85-88 were grown from concentrated CH2Cl2 or CH3CN solutions layered with Et2O, allowing for characterization of these complexes in the solid state. Of particular interest in these complexes is the relationship of the thienyl groups with respect to the pyridine rings. Planarity between these groups has significant implications in terms of electron delocalization out to the periphery of the molecule, influencing electron and energy transfer processes.   Figure 4-2. Solid state structure of [Ru(bpy)2(tL)][PF6]2 (85). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity.   134  Table 4-1. Selected bond lengths and angles for [Ru(bpy)2(tL)][PF6]2 (85) Bond angles (o)  Lengths (Å)  N1-Ru1-N2 78.48(10) N(1-6)-Ru1 2.053(2) – 2.068(3) N3-Ru1-N4 79.04(11)   N5-Ru1-N6 78.71(12)   Torsion angles (o)    C17-C12-C13-S2 -11.2(5) C2-C3-C4A-S1A 10.5(15)  In [Ru(bpy)2(tL)][PF6]2 (85, Figure 4-2), despite some disorder in one thiophene ring (the thiophene ring containing S1A can flip 180o to a position where the sulfur is pointing towards the ‘inside’ of the bipyridine plane), the rings are observed to be almost entirely coplanar with respect to the bipyridine rings with torsion angles of -11.2(5)° (C17-C12-C13-S2) and 10.5(15)° (C2-C3-C4A-S1A; Table 4-1). As discussed in this chapter, in solution, this is the expected excited state orientation, where in the ground state these rings are likely rotating along the C12- C13 and C3-C4A bonds.   Figure 4-3. Solid state structure of [Ru(bpy)2(btL)][PF6]2 (86). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity. 135   Table 4-2. Selected bond lengths and angles for [Ru(bpy)2(btL)][PF6]2 (86) Bond lengths (Å)    C3-C4 1.485(11) C7-C8 1.486(15) C16-C17 1.449(13) C20-C21 1.45(3) C8-S2 1.742(13) C7-S1 1.724(9) C20-S3 1.723(10) C21-S4 1.734(16) C16-C17 1.449(13) C3-C4 1.485(11) Torsion angles (o)    C15-C16-C17-S3 -176.6(8) S3-C20-C21-S4 -151(4) C12-C3-C4-S1 -173.1(8) S1-C7-C8-S2 -178.8(10)   The solid state structure of [Ru(bpy)2(btL)][PF6]2 (86, Figure 4-3) is comparable to that of [Ru(bpy)2(tL)][PF6]2 (85). In 86 the thiophene rings immediately adjacent to the bipyridine portion of the ligand are nearly planar with respect to the pyridine rings with torsion angles of - 176.6(8)°  (C15-C16-C17-S3) and -173.1(8)° (C12-C3-C4-S1; Table 4-2). These rings are slightly out of planarity with respect to the outer set of thiophene rings with torsion angles of - 151(4)°  (S3-C20-C21-S4) and -178.8(10)°  (S1-C7-C8-S2). The thienyl sulfur atoms (S1-S4) on adjacent thiophene rings are in a transoid arrangement relative to each other (S1 and S3 face to the ‘outside’ of the plane, while S4 and S2 point towards the ‘inside’ of the bipyridine plane).   136   Figure 4-4. Solid state structure of [Ru(bpy)2(sec-amL)][PF6]2 (87). Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, counterions and occluded solvent molecules omitted for clarity.  Table 4-3. Selected bond lengths and angles for [Ru(bpy)2(sec-amL)][PF6]2 (87)  Bond angles (o)  Lengths (Å)  C3-N2-C11 125.3(7) N2-C11 1.386(10) C8-N3-C16 128.3(7) N3-C16 1.376(11) N3-C16-C17 115.0(8) C16-O2 1.222(11) N2-C11-C12 115.2(7) C11-O1 1.208(10) C11-C12-O1 122.2(7) N3-C8 1.389 (10) C17-C16-O2 122.7(8) N2-C3 1.388(10)   C12-C11 1.472(11)   C16-C17 1.484(12) Torsion angles (o)    O1-C11-C12-S1 1.6(11) O2-C16-C17-S2 -2.7(12) C12-C11-N2-C3 -165.9(8) C3-C4-N2-C11 6.6(13) C8-N3-C16-C17 -176.7(8) C7-C8-N3-C16 -2.0(13)   The thiophene rings in [Ru(bpy)2(sec-amL)][PF6]2 (87, Figure 4-4) are also reasonably planar with the plane of the amide linkage, and the pyrdine rings (Table 4-3). This planarity is reflected in the torsion angles; 1.6(11)° (O1-C11-C12-S1) and -2.7(12)° (O2-C16-C17-S2).  Interestingly, the amide linkages both adopt a conformation in the solid state wherein the amide carbonyl oxygen is facing into the ‘center’ of the bipyridine plane; in other words, the two 137  oxygen atoms are pointed towards each other. In addition, much as in the structure of [Ru(bpy)2(tL)][PF6]2 (85), the thiophene sulfur atoms are also oriented in the same direction as the carbonyl oxygen atoms. No significant interactions with counterions or solvent molecules are observed in this structure.  As expected, replacement of the amide hydrogen with an ethyl group in [Ru(bpy)2(tert- amL)][PF6]2 (88, Figure 4-5) results in a dramatically different geometry at the amide linkage (Table 4-4). In 88, the thiophene rings are twisted out of the plane of the pyridine rings through the C3-N2 and C8-N3 bonds. This results in a conformation where the amide ethyl groups are oriented below the plane of the pyridine rings, and the thienyl moieties are located above the plane of the pyridine rings. Interestingly, the outcome is the formation of a pocket for a coordinating PF6 - anion. The anion is coordinated between the two amide ethyl groups and an adjacent pyridine ring. Some possible contacts are shown in Figure 4-5 (right), all of which have angles > 130o (C-H▪▪▪F), and relatively short distances < 3 Å. These types of interactions with weakly coordinating anions have been observed previously in bimetallic Re/Ru systems connected through amide linkages (with the interactions ocurring via the amide N-H),208 however C-H▪▪▪F hydrogen bound systems are also possible.209  138   Figure 4-5. Solid state structure of [Ru(bpy)2(tert-amL)][PF6]2 (88, left) and the same structure with one [PF6] - counterion and some possible C-H▪▪▪F contacts. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms and occluded solvent molecules omitted for clarity.  Table 4-4. Selected bond lengths, angles and contacts for [Ru(bpy)2(tert-amL)][PF6]2 (88)  Bond angles (o)  Lengths (Å)  C8-N3-C16 121.6(5) C8-N3 1.406(7) N3-C23-C24 112.2(5) N3-C16 1.382(7) C17-C16-N3 118.3(5) C16-C17 1.491(8) O2-C16-C17 119.8(5) N3-C23 1.478(8) O2-C16-N3 121.7(6) C3-N2 1.408(7) C3-N2-C11 125.5(5) N2-C11 1.369(8) C12-C11-O1 119.2(6) C11-C12 1.473(10) N2-C21-C22 112.8(5) C11-O1 1.224(7) C12-C11-N2 120.2(6) C16-O2 1.218(7) C21-N2-C3 115.9(5) N2-C21 1.464(8) Torsion angles (o)    C7-C8-N3-C23 61.1(8) S1-C12-C11-O1 6.0(8) C7-C8-N3-C16 -143.0(6) C3-N2-C21-C4 68.0(8) N3-C16-C17-C18 24(2) C4-C3-N2-C11 61.8(8) S2-C17-C16-O2 17.5(8) N2-C11-C12-C13 8.8(11) C-H▪▪▪F distances (Å)a  C-H▪▪▪F angles (o)a  H23A-F12 2.554 C22-H22A-F10 167.68 H24A-F11 2.743 C23-H23A-F12 134.39 H22A-F10 2.690 C24-H24A-F11 146.09 H44-F11 2.436 C44-H44-F11 164.71 aAs measured in CCDC Mercury 3.0200 139  Section 4.3.3 - Photophysical properties of complexes 85-90   Figure 4-6. (a) Absorption and emission spectra for [Ru(bpy)3][PF6]2 (1), [Ru(bpy)2(tL)][PF6]2 (85),  [Ru(bpy)2(sec-amL)][PF6]2 (87),  [Ru(bpy)2(tert-amL)][PF6]2 (88), and (b) absorption and emission spectra for [Ru(bpy)3][PF6]2 (1) and [Ru(bpy)2(btL)][PF6]2 (86) in CH3CN (λex = 450 – 490 nm).  [Ru(bpy)2(tL)][PF6]2 (85, Figure 4-6a) and [Ru(bpy)2(btL)][PF6]2 (86, Figure 4-6b) exhibit ground state absorption spectra with Ru dπ  π* (MLCT) bands in the visible region of the spectrum and with the UV region of the spectrum dominated by LC bands. These features, albeit bathochromically shifted (in the visible region), are comparable to those observed in [Ru(bpy)3][PF6]2 (1). In [Ru(bpy)2(btL)][PF6]2 (86), an additional transition centered at λmax = (a) (b) 140  400 nm (composed of two maxima) is observed and attributed to π  π* transitions localized on each of the bithienyl moieties.93 The bathochromic shift of the MLCT bands suggests electronic coupling between the central metal core and the peripheral bithienyl substituents. This increased degree of conjugation from the periphery to the metal center is further evidenced in the emission spectra of [Ru(bpy)2(tL)][PF6]2 (85) and [Ru(bpy)2(btL)][PF6]2 (86), where λem exhibits a bathochromic shift from 610 nm ([Ru(bpy)3][PF6]2) to 638 nm (85) and 675 nm (86). These findings suggest a narrowing of the band gap, resulting from an increase in conjugation within the ligands. Conversely, ground state absorption spectra for heteroleptic [Ru(bpy)2(sec-amL)][PF6]2 (87) and [Ru(bpy)2(tert-amL)][PF6]2 (88, Figure 4-6a) exhibit spectral features mirroring those observed in [Ru(bpy)3][PF6]2 (1). The spectra represent the sum of the individual chromophores in the system; the ligand-centered and the metal-centered bands are largely unaffected by one another (a small bathochromic shift is noted in the MLCT bands of these complexes relative to [Ru(bpy)3][PF6]2, Δλmax ≈ 10 nm). The emission maxima of 87 (623 nm) and 88 (634 nm) are slightly bathochromically shifted in comparison to the emission maximum of [Ru(bpy)3][PF6]2 (1, measured at 610 nm); possibly as a result of the electron donating character of the amide linkage.190,192 In order to reconcile these findings, and to determine what role the amide linkage (if any) may be playing in the photophysical behavior of these complexes, a combination of emission quantum yield (Φ), excited state lifetime (τes) and emission lifetime (τem) data were compared. These findings are reported in Table 4-5, and serve as a starting point for the comparison of complexes 85-90.  141  Although the emission quantum yield values vary, it is readily apparent from the data in Table 4-5 that where complexes with amide-linked thiophene substituents have quantum yields comparable to [Ru(bpy)3][PF6]2 (1), their directly bound analogs have quantum yields that are approximately three times higher. Similar findings have been reported by McCusker et al,105,210 in homoleptic Ru2+ complexes with 4,4'-diphenyl-2,2'-bipyridine (dpb) ligands of the type [Ru(dpb)3] 2+ (91). McCusker and coworkers observed that the quantum yield of [Ru(dpb)3] 2+ (91) was approximately three times greater than that observed for [Ru(bpy)3] 2+, and concluded that these deviations originated from a planarization of the phenyl rings with respect to the bipyridine rings once this complex was excited via the lowest energy ground state absorption.210 This excited state behavior afforded an increase in conjugation of the peripheral ligands, resulting in a lower energy emission maximum and a higher quantum yield of emission. By comparison to the work of McCusker et al., a similar excited state behavior is expected to occur in complexes [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(btL)][PF6]2 (86) and [Ru(tL)3][PF6]2 (89), regardless of the planarity of the thienyl rings in the solid state.    142  Table 4-5. Selected photophysical and electrochemical properties of the complexes described in this chapter Compound λem a   (nm) Φem a,c   τem a  (µs) τes b   (µs) kr  (105 s-1) knr  (105 s-1) [Ru(bpy)3][PF6]2 610 0.095 103 0.85534 0.925 0.73 11.0 85 638 0.33 1.98 2.3 1.7 3.4 86 675   ~15 - - 87 623 (CH3CN) 620 (CH2Cl2) 623 (H2O)  0.11 0.876 (CH3CN) 1.016 (CH2Cl2) 0.502 (H2O) 0.836 1.3 10.2 88 634 (CH3CN) 620 (CH2Cl2) 644 (H2O)  0.12 0.824 (CH3CN) 0.728 (CH2Cl2) 0.315 (H2O) 0.724 1.5 10.7 89 647 0.35 1.28 1.03 2.7 5.1 90 642 0.08 0.451 0.450 1.8 20.3 All measurements performed in CH3CN, unless noted; solutions were prepared in air and then purged with Ar for 15 minutes. In the case where measurements were taken in different solvents samples were first dissolved in CH3CN (13% of final volume) and then made up to volume with the target solvent (CH2Cl2 or H2O). aλex = 453 nm. bλex = 355 nm. cAbsolute quantum yield at room temperature, error estimated to be ≤ 10% based on prior experiments (Table 2-1).   Rates of radiative and non-radiative decay were calculated using equations 4-1 and 4-2:211            ⁄   (4-1)               (4-2) The rates of radiative decay for the directly linked complexes are greater than that of [Ru(bpy)3][PF6]2 (1) and the amide linked complexes. As summarized by McCusker and coworkers,105 the rate of radiative decay is proportional to the product of the square of the transition dipole moment and the cube of the energy separating the two radiatively coupled states (in other words, the emission energy). Here, the excited state transition dipole (which is proportional to the magnitude of the charges in the charge separated excited state multiplied by 143  the distance separating them) is expected to play a large role, as considering solely the emission energy (the second term in the proportionality relationship described above) predicts the opposite trend of what is observed experimentally. An excited state where the photoexcited electron is delocalized onto the peripheral thienyl moieties should result in a larger excited state dipole moment. These observations were initially reported by McCusker and coworkers (for [Ru(dpb)3] 2+ 91),105 and hold true for the directly bound systems described in this work. The formation of an excited state with a greater degree of electron delocalization results in a longer excited state (as well as emission) lifetime. This is clearly observed in the case of [Ru(bpy)2(tL)][PF6]2 (85). In complex [Ru(bpy)2(btL)][PF6]2 (86), in addition to the long lifetime expected for the delocalized MLCT state, additional energy reservoir contributions (similar to those discussed in prior sections of this thesis) are also possible, due to the relatively low-lying triplet state localized on bithiophene.122 From the transient absorption spectroscopy (discussed later in this section), it becomes readily apparent that the excited state in 86 differs significantly from that observed for 85. Surprisingly, the lifetime of 89 is only mildly enhanced in relation to [Ru(bpy)3][PF6]2  (1), suggesting that a system with mixed ligands, ML2L', may experience contributions from both ligand types in the excited state. In stark contrast to [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(btL)][PF6]2 (86) and [Ru(tL)3][PF6]2 (89), amide-linked complexes [Ru(bpy)2(sec-amL)][PF6]2 (87), [Ru(bpy)2(tert- amL)][PF6]2 (88) and [Ru(sec-amL)3][PF6]2 (90) exhibit lifetimes (both excited state and emission) that are comparable to that of [Ru(bpy)3][PF6]2 (1). Despite the observed low energy emission maxima for these complexes, no lifetime enhancement was observed (as indicated by much higher rates of non-radiative decay). These findings are in contrast to one another: the emission results suggest a greater degree of delocalization in the ligand, while lifetime 144  measurements suggest that the degree to which delocalization is occurring is much lower than that in the directly bound complexes. Due to the partial double bond character of the amide linkage,189 electronic communication and electron transfer over the amide bond are expected.212 Perhaps more interesting is the lower energy emission maximum in [Ru(bpy)2(tert- amL)][PF6]2 (88) in comparison to [Ru(bpy)2(sec-amL)][PF6]2  (87). In complex 88, as evidenced from the solid state structure, installing an ethyl group in place of the proton at the amide nitrogen results in a ‘twisted’ amide bond arrangement where, regardless of the excited state behavior, planarization of the thiophene with respect to the pyridine is unlikely.206 This limits the degree of conjugation possible within the ligand. Moreover, measurement of the emission lifetimes of 88 in different dielectric constants solvents (CH3CN vs. CH2Cl2) results in almost no change in lifetime (a small decrease; from 0.824 µs to 0.728 µs), as well as a corresponding bathochromic shift in the emission maximum. In 87, varying the solvent from CH3CN to CH2Cl2 results in a lifetime increase (suggesting a stabilization of the excited state in a solvent of lower polarity, CH2Cl2), but little shift in the emission maximum. Both complexes exhibit a shorter lifetime in H2O than in CH3CN, however this may be attributed to hydrogen bond formation between the amide linkage and surrounding environment. In some donor-chromophore-acceptor (D-C-A) systems, hydrogen bonding has been shown to play an essential role in shaping the character of the excited state.136,137,208 Increasing the dielectric constant, or polarity of the solvating medium is expected to stabilize (and lower) the energy of a polar excited state.213 One possible polar excited state that may be formed in 88 (and in the other heteroleptic complexes), is an LMCT state where an electron is transferred from one of the peripheral ligands to Ru3+ formed on photoexcitation. Based on the solid state structure of [Ru(bpy)2(tert- amL)][PF6]2 (88), incorporating an N-ethyl group into the thienyl containing ligand decreases the 145  centroid-to-centroid distance of the thienyl group to the Ru core to ~7.4 Å. It is possible that on photoexcitation a thienyl moiety is behaving as a reductive quencher for Ru3+. Another possibility is an LMCT state where an unsubstituted 2,2'-bipyridine ligand is acting to quench Ru3+ (if the amide substituted ligand is behaving as the acceptor in the MLCT state). Although formation of an LMCT state is an attractive proposition, with implications in vectorial charge separation, in the case of  [Ru(bpy)2(tert-amL)][PF6] (88), it is also possible that replacing the hydrogen atom at the amide nitrogen with an ethyl group results in a minor change in the electronics of the linkage. The installation of an electron donating ethyl group may strengthen the electron donating character of the nitrogen, resulting in a greater perturbation of the MLCT acceptor orbital (and the resulting bathochromic shift of the emission maximum).214 Comparison of the time-resolved excited state spectra of complexes [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(sec-amL)][PF6]2 (87), and [Ru(bpy)2(tert-amL)][PF6]2 (88) further supports the hypothesis that a different excited state is being formed in all three of these complexes (Figure 4- 7). Complex 87 (Figure 4-7a) exhibits an excited state spectrum mirroring that of [Ru(bpy)3][PF6]2 (1, Figure 4-8), with a strong absorbance at ca. 375 nm attributed to the formation of a bipyridine anion in the MLCT excited state.24,31,32 A bleaching of the ground state MLCT absorbance band is observed between 400 – 500 nm. This is attributed to the formation of Ru3+, (and concomitant depletion of Ru2+ species). A weak positive feature in the TA spectrum is observed centered at ~550 nm, and has been previously attributed to π  π* transitions on a reduced bipyridine moiety.24 146     Figure 4-7. Transient absorption difference spectra of complexes [Ru(bpy)2(sec-amL)][PF6]2 (87) (a), [Ru(bpy)2(tert-amL)][PF6]2 (88) (b), [Ru(bpy)2(tL)][PF6]2 (85) (c) in CH3CN (λex = 355 nm, fwhm = 35 ps). (a) (b) (c) 147  The same higher energy (centered at ca. 375 nm) feature is observed in the excited state spectrum of [Ru(bpy)2(tert-amL)][PF6]2 (88, Figure 4-7b), concomitant with the formation and disappearance of a broad low energy feature centered at ~650 nm. This feature, is analogous to one reported by McCusker et al. in oxidative spectroelectrochemistry of [Ru(dpb)3] 2+ (91).210  McCusker and coworkers attribute the growth of such a broad low energy band to the formation of an LMCT state.19 As previously noted, incorporation of a tertiary alkyl-amide may increase the electron donating character of the amide N atom. If this low energy band is the result of π  π* transitions on a reduced bipyridine moiety (in this case the bipyridine appended to the amide substituent), one possibility is that this band would be expected to shift bathochromically through interactions with the electron donating N atom. Once again a depletion of ground state Ru2+ species is observed in a bleach feature in the 400 – 500 nm region. [Ru(bpy)2(tL)][PF6]2 (85) exhibits the most complicated excited state spectrum (Figure 4- 7c) of the series, where outside of the higher energy absorbance at ~390 nm (bathochromically shifted due to an extension of conjugation previously observed in the ground state spectrum of this complex), and the depletion of the ground state Ru2+ species, two features are observed in the low energy portion of the spectrum. One feature, centered at 550 nm, mirrors that observed in [Ru(bpy)2(sec-amL)][PF6]2 (87), while the low energy shoulder centered at 650 nm mirrors that reported for [Ru(bpy)2(tert-amL)][PF6]2 (88). This suggests that the excited state of 85 contains a combination of features observed for the excited state species of 87 and 88: possibly an LMCT band, and transitions localized on a reduced bipyridine.24,210 A comparison of the excited state spectra of the complexes discussed above and [Ru(bpy)3][PF6]2 (1) is shown in Figure 4-8, illustrating the differences between the excited state features of these four complexes within the first 300 ns after excitation. 148   Figure 4-8. TA difference spectra comparing [Ru(bpy)2(tL)][PF6]2 (85, blue), [Ru(bpy)2(sec- amL)][PF6]2 (87, black), [Ru(bpy)2(tert-amL)][PF6]2 (88, red) and [Ru(bpy)3][PF6]2 (1, teal) in CH3CN (λex = 355 nm).  It is difficult to compare [Ru(bpy)2(btL)][PF6]2 (86) to the complexes discussed above due to the possibility of multiple states interfacing in the excited state (due to the incorporation of bithienyl groups, and the possibility of their corresponding triplet states being formed). The excited state spectrum of 86 differs significantly from that observed for thienyl analog, [Ru(bpy)2(tL)][PF6]2 (85, Figure 4-7b). In the excited state spectrum of 86 (Figure 4-9a), two prominent bleach features are observed; a feature at higher energy (~400 nm) corresponding to a bleaching of the ground state bithienyl π  π* absorbance, and a lower energy bleach feature (~500 nm) corresponding to a depletion of the ground MLCT bands as described for the previous heteroleptic complexes. In addition to these two bleaches, three prominent positive absorbance features are observed a high energy feature centered at 450 nm (the intensity of which may be lowered by overlap with the negative features on either side), a low energy feature centered at 575 nm, and a low energy shoulder associated with this absorbance.  149   Figure 4-9. TA difference spectra of (a) [Ru(bpy)2(btL)][PF6]2 (86) and (b) [Ru(bpy)2(tL)][PF6]2 (85), [Ru(bpy)2(btL)][PF6]2 (86) and [Ru(bpy)3][PF6]2 (1) in CH3CN (λex = 355 nm, fwhm = 35 ps).  In Chapter 2 (Sections 2.3.2 and 2.3.5), the excited state spectra for a series of 1,10- phenanthroline amide-linked thiophene Ir3+ and homoleptic Ru2+ complexes were shown. In those studies, it was determined that contributions to positive absorption features at higher energies (~420 nm, Figure 4-9a) arose from triplet states localized on peripheral bithienyl moieties, as well as reduced phenanthroline groups. By comparison, it can be suggested that the higher energy feature observed in the excited spectrum of [Ru(bpy)2(btL)][PF6]2 (86) is attributable to a triplet state localized on bithienyl moieties appended to the bipyridine.122 This is additionally supported by the exceedingly long excited state lifetime (τ = 15 µs), due to equilibration of multiple excited states.  As previously mentioned in the case of directly bound [Ru(bpy)2(tL)][PF6]2 (85), the long lifetime in [Ru(bpy)2(btL)][PF6]2 (86) likely also arises from the planarization of the bithienyl moieties in the excited state, and an increase in delocalization of the photoexcited electron over this new, longer conjugation pathway. As noted, this is also supported by the bathochromic shift in the emission maximum. The two low energy features observed in the excited state spectrum of (a) (b) 150  86 are reminiscent of similar features observed in 85 and suggest that a similar excited state is formed in both cases. If this is the case, it is also possible that the feature centered at 450 nm in the excited state spectrum of 86 may also be attributed to the formation of a bithiophene cation (previously prepared by radiolysis with λmax = 425 nm), 110,111 in addition to formation of a reduced bipyridine anion. Here, an LMCT state may exist where the Ru3+ is reductively quenched by a bithienyl group, resulting in a long-lived charge separated state.   Figure 4-10. Emission and absorption spectra of [Ru(tL)3][PF6]2 (89), [Ru(sec-amL)3][PF6]2 (90) and [Ru(bpy)3][PF6]2 (1) in CH3CN (λex = 490 nm).  Homoleptic complexes [Ru(tL)3][PF6]2 (89, λem = 647 nm) and [Ru(sec-amL)3][PF6]2 (90, λem = 642 nm) exhibit comparable emission maxima (Figure 4-10), that are both significantly bathochromically shifted when compared to [Ru(bpy)3][PF6]2. Much as in heteroleptic complexes [Ru(bpy)2(tL)][PF6]2 (85) and [Ru(bpy)2(sec-amL)][PF6]2 (87), both 89 and 90 exhibit a ground state absorption spectrum similar to that of the unsubstituted [Ru(bpy)3][PF6]2  (1, Figure 4-10), however, in both complexes, the low energy MLCT band (centered around 480 nm 151  in both) is bathochromically shifted. From these data, and in general terms, the homoleptic complexes appear to behave in a similar fashion to their heteroleptic counterparts. Of additional interest is the modest increase in emission lifetime observed for [Ru(tL)3][PF6]2 (89) when compared to unsubstituted [Ru(bpy)3][PF6]2 (1) and [Ru(bpy)2(tL)][PF6]2 (85). These differences suggest that having a mixture of substituted and unsubstituted ligands plays a role in shaping the nature of the excited state formed in these complexes, regardless of the linkage separating the thiophene from the metal center. The bathochromically shifted emission observed in [Ru(sec-amL)3][PF6]2 (90) is expected based on previously reported studies of Ru2+ complexes with similar secondary amide substituents. Meyer and coworkers,190 as well as George et al.191 have reported an analogous shift in the emission due to the slight electron-withdrawing character of the amide linkage (in these examples, the amide carbonyl was linked to the pyridine ring). In the case of the sec-amL (83) ligand, attachment of the amide linkage to the pyridine ring via the amide N atom should result in a slight increase in the energy level of the acceptor (bipyridine) HOMO; producing a narrowing of the HOMO-LUMO gap, and a corresponding bathochromic shift in the emission (and in the ground state absorption spectrum). The magnitude of the bathochromic shift in the emission of the heteroleptic [Ru(bpy)2(sec-amL)][PF6]2 (87) complex is not as large as the homoleptic complex, possibly due to contributions from the other unsubstituted ancillary ligands. This narrowing of the HOMO-LUMO gap, and lowering of the emission energy may account for the shorter excited state lifetime observed in [Ru(sec-amL)3][PF6]2 (90). 211 Conversely, the bathochromic shift in the absorption and emission spectra of [Ru(tL)3][PF6]2 (89) correlate to the same principles observed in the analogous heteroleptic complex: a planarization of the thiophene rings, and a corresponding delocalization of the 152  photoexcited electron. Here, the shorter lifetime may once again be a result of the lack of contributions from unsubstituted ligands.  Figure 4-11. Comparison of extended TA difference spectra of complexes [Ru(tL)3][PF6]2 (89, red) and [Ru(sec-amL)3][PF6]2 (90, black) (t = 0 – 50 ns, CH3CN, λex = 355 nm, fwhm = 35 ps).  Comparing the excited state difference spectra for [Ru(tL)3][PF6]2 (89) and [Ru(sec- amL)3][PF6]2  (90) offers some insight into the nature of the excited state manifold in these two complexes (Figure 4-11). The spectrum for 89 closely resembles that of [Ru(bpy)2(tL)][PF6]2 (85), with a positive feature centered around 400 nm, and a bleaching in the ground MLCT absorption region. The same is true of the spectrum observed for 90, a positive feature is observed at ~375 nm, while a broad low energy absorption is observed centered at 600 nm. Examining the excited state spectrum towards the UV (wavelengths below 350 nm) reveals another difference between these two complexes. Complex 90 exhibits a narrow absorption centered at 325 nm that is absent in the spectrum of 89.  153  As previously described, a thiophene moiety may act to reductively quench Ru3+ resulting in formation of a hole on a thienyl moiety, as well as an electron localized on a bipyridine moiety. This LMCT state may be giving rise to this previously unobserved high energy feature (λmax = 325 nm). Transient absorption of [Ru(sec-amL)3][PF6]2 (90) in the presence of low concentrations of methyl viologen (MV2+) a well-studied electron acceptor result in quenching of the positive absorption band centered at 400 nm, while the band at 325 nm remains unchanged (Figure 4-12a).  Figure 4-12. (a) Excited state spectra of [Ru(sec-amL)3][PF6]2 (90) in the presence of MV 2+ (~1 mM) and (b) in the presence of TTF (~0.6 μM) in CH3CN (t = 0 – 50 ns, λex = 355 nm, fwhm = 35 ps).  Addition of a known electron donor, tetrathiafulvalene (TTF) in a similar bimolecular quenching experiment (Figure 4-12b) results in what appears to be quenching of both high energy features. Although conflicting, the results of these experiments may still indicate the presence of a LMCT state in [Ru(sec-amL)3][PF6]2 (90). Addition of MV 2+ supports this postulate, where addition of TTF may simply result in a quenching of the Ru3+ itself, totally modifying the overall excited state manifold. Due to the close energetic proximity of the excited (a) (b) 154  state species possible in these complexes, it becomes difficult to fully assess what changes may be taking place in the presence of other electron rich/poor species. Section 4.4 – Conclusions  The series of homoleptic and heteroleptic Ru2+ complexes with thienyl substituted 2,2'- bipyridines reported in this chapter reveal that although these complexes exhibit similar features in their respective solid state structures, a comparison of the photophysical properties of these complexes shows a number of different trends.  In the series of heteroleptic complexes, complexes with amide-bound thienyl groups exhibit quantum yields and lifetimes that are lower than those observed for complexes with directly bound thienyl groups. However, the ground state absorption spectra and emission maxima (and therefore energies) of the amide bound complexes exhibit a bathochromic shift when compared to [Ru(bpy)3][PF6]2 (1). A similar, but of larger magnitude, bathochromic shift in the directly bound complexes is attributed to delocalization of the photoexcited electron out onto the peripheral thiophene rings. This polar, delocalized excited state is supported by correlation of the reported data to experimental data previously reported for a complex bearing ligands that are expected to behave in a similar fashion: [Ru(dpb)3] 2+ (91).105  In the case of heteroleptic complex [Ru(bpy)2(tert-amL)][PF6]2 (88), where a polar excited state is also anticipated; emission lifetime experiments with varying solvent polarity, as well as comparison of the radiative rates support the formation of such a polar excited state. In the case of this tertiary amide complex, the excited state may be comprised of a LMCT (reductive quenching of Ru3+ by a peripheral thienyl moiety) state, where the peripheral thiophene rings are brought into close proximity of the metal center (~7.4 Å).  155  In the case of the homoleptic complexes, these trends are generally preserved. However, both the amide and directly bound complexes exhibit lifetimes that are only mildly perturbed from [Ru(bpy)3][PF6]2 (1), while in both cases, the emission maximum is bathochromically shifted in relation to the unsubstituted analog. Meyer and coworkers have previously reported that in mixed ligand (ML2L') polypyridyl Ru 2+ complexes bearing amide-appended 2,2'- bipyridine ligands, the amide ligand behaves as the acceptor ligand.190 In the heteroleptic series of complexes, the amide ligand may behave as the acceptor, but the excited state may also have contributions from the remaining unsubstituted ligands (which are energetically similar to the substituted ligand), while in the homoleptic complexes this is no longer possible. This produces an excited state characterized by the properties of the substituted 2,2'-bipyridine ligands with no extraneous contributions. From these studies, it appears that the amide linkage plays a minor role in shaping the excited state of these complexes. In both the heteroleptic and homoleptic cases the amide linkage behaves as a mild electron donor, resulting in a bathochromic shift of the emission, with minor perturbations of the ground state spectrum. Excited state spectroscopy suggests that in the heteroleptic complexes, despite the amide-linkage substituted ligands behaving as the acceptor ligands, the excited state may also receive contributions from the unsubstituted ligands, resulting in the formation of LMCT states.   156  CHAPTER 5  Conclusions and future work  Section 5.1 – Conclusions  The goal of the work presented in this thesis, as outlined in Section 1.6, was to enhance the desired excited state characteristics of complexes for use in artificial photosynthetic assemblies. One possible enhancement is to extend the excited state lifetime of these complexes: as the lifetime of CS states is increased, charge recombination rates approaching those of natural photosynthesis may be realized. Another enhancement is to generate CS states that transiently store enough energy to drive the catalytic processes that in artificial photosynthesis store energy in high energy chemical species.  In Chapter 2, a new series of ligands based on 1,10-phenanthroline was introduced (27-29). Thiophene oligomers in these 1,10-phenanthroline ligands were appended to the diimine via an amide linkage at the 5- position. Heteroleptic and homoleptic complexes (31-34) incorporating these ligands were shown to exhibit excited state behavior that was perturbed from that expected for [Ru(phen)3][PF6]2 (30) through the inclusion of the aforementioned oligomers. More specifically, integrating bithienyl moieties into both homoleptic and heteroleptic Ru2+ complexes resulted in a significant enhancement of the excited state lifetime. Homoleptic complex [Ru(phen-btL)3][PF6]2 (32) has an excited state lifetime (τ ≈ 7 μs) that is approximately 14 times longer than that of unsubstituted [Ru(phen)3][PF6]2 (30), while heteroleptic complex [Ru(phen)2(phen-btL)][PF6]2 (33) was shown to have an excited state lifetime that is 6 times longer than that of [Ru(phen)3][PF6]2 (30). Due to the close energetic proximity of the 3LC state localized on bithiophene, this lifetime extension is attributed to 157  equilibration of a 3LCBT state and the 3MLCT state. Additionally, through spectroelectrochemical measurements, it was determined that a third state is interfacing with the two equilibrating states. This third state was determined to be a 3ILCT state, where the bithienyl moiety acts to reductively quench Ru3+, and a hole is localized on the bithienyl moiety (characterized by a correlation of the reductive spectroelectrochemistry and the transient absorption spectra). The driving force (ΔETG°) for the formation of this state was found to be -0.14 eV. In addition, this long-lived 3ILCT state was found to store an appreciable amount of energy, ΔG° ≥ 1.9 eV, resulting in a reorganization energy that may lie in the Marcus inverted region.  Matching the excited state energy of the organic chromophore and 3MLCT state is crucial to the formation of a two-state, or subsequent three-state equilibrium (Section 1.3). It was found that the bithiophene unit is the ideal length to form these equilibrated states. Through the study of [Ru(phen)2(phen-ttL)][PF6]2 (34), a complex bearing a phen ligand with a terthienyl moiety (29), it was observed that the 3LC state localized on terthiophene lies lower in energy than the 3LC state localized on bithiophene, resulting in an excited state in the heteroleptic complex that is predominantly 3LC (terthiophene) in character. This behavior is similar to that reported by Ziessel et al. for complex 22 (Section 1.4.1).76  Depending on the coordination environment around the metal center, cyclometalated Ir3+ complexes have 3MLCT energies that are similar to those of Ru2+ polypyridyl complexes. Combining bithienyl ligand phen-btL (28) and Ir3+ with ppz cyclometalating ligands gave complex [Ir(ppz)2(phen-btL)][PF6] (44). Mirroring the behavior observed for [Ru(phen)2(phen- btL)][PF6]2 (33) and [Ru(phen-btL)3][PF6]2 (32), the excited state lifetime of [Ir(ppz)2(phen- btL)][PF6] (44, τ = 12 μs) was 12 times longer than that observed for [Ir(ppz)2(phen)][PF6] (42). Through a correlation of the nature of the emission, and the transient absorption spectroscopy of 158  [Ir(ppz)2(phen-btL)][PF6] (44) it was determined that this long lifetime was a rare example of a two-state energy reservoir equilibrium forming within an Ir3+ complex, further verifying the utility of the phen-btL (28) ligand as a triplet reservoir. Finally, complexes bearing phen-btL (28) were shown to undergo electropolymerization to give polymeric films on ITO electrode surfaces. Films grown on ITO substrates were shown to retain many of the photophysical properties of their respective monomers: [Ru(phen-btL)3][PF6]2 (32) and [Ru(phen-btL)2(dppz)][PF6]2  (50). On irradiation (λmax = 365 nm), a current was generated in a three electrode cell with the films on ITO acting as the working electrode. This sort of photocurrent generation indicates that these films may be used as electrodes in PES cells, where a stable connection between the light absorbing assembly and the electrode surface is required.  Although the complexes discussed in Chapter 2 exhibit many favorable properties in the context of photochemical energy conversion, or artificial photosynthesis, the 3ILCT formed in these complexes lacked directionality, and the overall spatial separation between the excitonic charges was relatively low. In order to generate vectorial charge separation in complexes bearing these ligands, a number of new Ru2+ complexes bearing both phen-btL ligands (28) as donor moieties and large planar polypyridyl ligands dppz (47), tpphz (48) and tatpp (49) as laminate acceptor ligands (a designation resulting from the two acceptor orbitals localized on the ligand; laminated over one another) were introduced in Chapter 3 (50-52). Complexes [Ru(phen-btL)2(dppz)][PF6]2 (50, τem = 2.2 μs), [Ru(phen-btL)2(tpphz)][PF6]2 (51, τem = 3.6 μs) and [Ru(phen-btL)2(tatpp)][PF6]2 (52, τes = 7.0 μs) were all determined to have both excited state and in the case of tpphz (51) and dppz (50) complexes, emission lifetimes that were 3, 4 and 14 times longer than their unsubstituted phen analogs (65, 53, 54), respectively. In 159  the case of the emissive dppz (50, 65) and tpphz (51, 53) adducts, the emission energies indicated that the 3MLCT excited state was localized on the proximal orbital, or the orbital localized on the phenanthroline portion of the laminate ligand that is closest to the metal center (a 3MLCTprox state). The long lifetime of these states was found to be fueled via equilibration with a 3LC state localized on the bithiophene moieties, much as in the complexes reported in Chapter 2. In tatpp complexes such as [Ru(phen)2(tatpp)][PF6]2 (54) it was determined that the lowest- lying excited state is a 3LC state localized on the tatpp (3LCtatpp), and equilibration with states such as a 3LCBT state in [Ru(phen-btL)2(tatpp)][PF6]2 (52) are unlikely due to the energetic mismatch between the 3MLCTprox, 3LCtatpp and 3LCBT states. It was determined that the long lifetime of [Ru(phen-btL)2(tatpp)][PF6]2 (52) results from equilibration of the 3MLCT localized on the distal phenazine portion of the tatpp bridge (3MLCTdist) with a 3ILCT state where a bithiophene moiety acts to reductively quench Ru3+ (Scheme 5-1).  Scheme 5-1.  160  It has been shown that the environment surrounding the laminate ligand can influence whether the 3MLCTdist or 3MLCTprox is the lowest lying excited state. 145,166 In Chapter 3, it was demonstrated that coordinating a Zn2+ ion in the open coordination site at the distal end of tpphz (48) and tatpp (49) ligands also modulates whether or not the 3MLCTdist state is the lowest lying state (i.e. coordinating Zn2+ to the open coordination site results in the photoexcited electron localizing in an orbital spatially far away from the metal center). This was confirmed in [Ru(phen-btL)2(tpphz)][PF6]2 (51), where on coordination of Zn 2+ the emission maximum shifted to a much lower energy than that of the noncoordinated analog, signalling the formation of the 3MLCTdist state. Although this state was found to have a lifetime (τes = 0.131 μs) much shorter than the Zn2+ free state,  it was determined to be longer lived than the corresponding Zn2+- coordinated state in the analogous unsubstituted complex [Ru(phen)2(tpphz)][PF6]2 (51Zn, τes = 0.081 μs). Such an extension of the lifetime may arise from the formation and equilibration of a 3ILCT state much as in the case of [Ru(phen-btL)2(tatpp)][PF6]2 (52). This effect was enhanced in [Ru(phen-btL)2(tatpp)][PF6]2 (52) where on Zn 2+ coordination the lifetime of the 3MLCTdist state was significantly longer (τes = 0.15 μs) than that of the unsubstituted complex [Ru(phen)2(tatpp)][PF6]2 (54) with coordinated Zn 2+ (τes = 0.004 μs).  The energy stored in the 3ILCT state formed in [Ru(phen-btL)2(tpphz)][PF6]2 (51) was estimated to be 1.41 eV, with a charge separation distance of ca. 11 Å (centroid of the bithienyl moiety to the centroid of the tpphz moiety). In [Ru(phen-btL)2(tatpp)][PF6]2 (52) the transiently stored energy of the 3ILCT state was estimated to be 0.98 eV. In the tatpp complex, although the stored energy is lower, the charge separation distance is increased to ca. 14 Å.  The complexes bearing laminate acceptor ligands presented in Chapter 3 are examples of D-C-A triads that may be used as the primary source of charge separation in artificial 161  photosynthesis (Section 1.2.2), a crucial step in shuttling charges to catalytic centers where catalysis to give small, high energy species takes place. In effect, the D-C-A triads in Chapter 3 begin to mimic the electron cascade that occurs in natural photosynthetic centers, by storing an appreciable amount of energy and spatially separating the charges formed on photoexcitation. In Chapter 4, the role of the amide linkage in the formation of excited states such as those discussed in Chapters 2 and 3 was elucidated through the study of a number of new Ru2+ complexes (85-88). Here, the chelating diimine was varied from 1,10-phenanthroline to 2,2'- bipyridine, and thienyl moieties were appended with both secondary and tertiary amide linkages at the 4,4'- positions of the diimine, as well as being directly bound (77, 78, 83, 84). Through the study of these complexes, it was determined that the thienyl moieties, regardless of the nature of the linkage, exist in a planar conformation with respect to the pyridine rings of 2,2'-bipyridine in the solid state. Through comparison of excited state and ground state spectroscopic data, it was found that complexes with directly bound thienyl linkages (85, 86) have bathochromically shifted emission maxima, as well as longer excited state lifetimes (τ = 2-15 μs) than their amide bound counterparts (87, 88). The formation of a polar 3MLCT excited state delocalized onto the thiophene or bithiophene rings in these complexes was found to be responsible for the long lifetimes; with slower rates of non-radiative decay.  In complexes with amide bound thienyl moieties, emission and excited state lifetimes were found to mirror those of unsubstituted [Ru(bpy)3][PF6]2 (1, τ ≈ 1 μs). In complexes with amide bound thienyl groups (87, 88), some variations by way of the electron donating nature of the amide linkage are observed in the excited state (with respect to the excited state behavior of 162  [Ru(bpy)3][PF6]2). In addition, bands attributed to contributions from LMCT states were also observed in the transient absorption difference spectra of these complexes.  Ultimately, any excited state contributions from the amide linkage appear to be relatively minor. Comparison of the amide linked complexes (87, 88) to complexes where the thienyl moiety is directly bound to the 2,2'-bipyridine ligand (85, 86), suggests that despite the partial double bond character of the amide linkage there is no significant electronic coupling between the peripheral thiophene and the metal center. Significant communication between the two chromophores would manifest itself in comparable excited state behavior between complexes bearing ligands with amide linked and directly bound thienyl groups. The work discussed in this thesis illustrates that through strategic ligand design, and by pairing compatible donor, acceptor and chromophore moieties, long-lived high energy excited states may be realized on photoexcitation. In the complexes presented in this thesis, these long- lived excited states are obtained through equilibration of three energetically comparable excited states. In terms of extending the excited state lifetimes of D-C-A triads for artificial photosynthesis, a three-state strategy is one that has been previously unexplored. The complexes discussed within this thesis, particularly those investigated in Chapter 3, are good candidates as reaction centers (specifically, as the site where initial charge separation takes place) in artificial photosynthetic constructs.  Section 5.2 – Future work It has previously been shown that laminate ligands such as tatpp may behave as multielectron acceptor and storage units.138,163,182 Catalytic processes within natural and artificial photosynthesis are often multielectron processes. In the context of this work, two photon 163  excitation of complexes such as [Ru(phen-btL)2(tatpp)][PF6]2 (52) may lead to excited state species where multiple electrons are localized on the tatpp moiety. In addition, tatpp moieties readily accept protons, and therefore these types of complexes may be novel catalysts for proton- coupled, multi-electron transfer reactions.182 Two photon transient absorption experiments have become increasingly popular for the study of natural photosynthetic constructs,215 and such experiments here may be used to probe whether storage of multiple electrons on the tatpp subunit is feasible, as well as the lifetime of such a state. The formation of a doubly reduced tatpp laminate ligand would satisfy element 5 of artificial photosynthesis, as described by Meyer et al. (Section 1.2). It may be possible to further enhance the suitability of the D-C-A triads reported in Chapter 3 for artificial photosynthesis by incorporating catalytic reaction centers into the open coordination sites of [Ru(phen-btL)2(tpphz)][PF6]2 (51) and [Ru(phen-btL)2(tatpp)][PF6]2  (52). Mixed metal, dinuclear complexes bearing tpphz ligands as bridges have previously been shown to behave as photocatalysts for proton reduction.216 Coordination of a –Pd(Cl)2 moiety to the open coordination site of the complexes discussed in Chapter 3 may give new supramolecular photocatalysts for these types of processes and satisfy element 6 of artificial photosynthesis (Section 1.2). Furthermore, varying the solvent environment around these assemblies may lend some insight into the electron transfer dynamics of these multielectron processes. Complexes bearing laminate polypyridyl ligands have been shown to aggregate in solution (Section 3.3.1). Instigating formation of well-ordered aggregates of complexes such as [Ru(phen- btL)2(tatpp)][PF6]2 (52) by varying the conditions under which aggregates are formed may lead to formation of aggregate structures that are capable of charge transfer over nanoscopic distances. On photoexcitation, electrons may be shuttled to the tatpp core of these aggregates, 164  while holes may accumulate at the periphery. This type of arrangement may lead to the formation of molecular wires, activated on irradiation. Electropolymerization of [Ru(phen-btL)2(dppz)][PF6]2 (50) on ITO electrodes gives surfaces that may have ‘free’ dppz moieties exposed to the environment outside of the electrode. Ligands such as dppz (47) have been shown to intercalate DNA, and a conductive surface functionalized with ‘free’ dppz moieties may interact with DNA in solution. 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Biotechnol. 2003, 21, 1192.     177  APPENDIX 1  Figure A1-1. Normalized absorbance spectra of [Ru(phen)3][PF6]2 (30, black), [Ru(phen- tL)3][PF6]2 (31, blue), [Ru(phen-btL)3][PF6]2 (32, teal), [Ru(phen)2(phen-btL)][PF6]2 (33, red).  Figure A1-2. Time resolved transient absorption decay curve of [Ru(phen-tL)3][PF6]2 (31) with monoexponential fit shown in red (410 – 480 nm). 178    Figure A1-3. Time resolved transient absorption decay curves of [Ru(phen-btL)3][PF6]2 (32) at various wavelengths with monoexponential fits shown in black and red. 179    Figure A1-4. Time resolved transient absorption decay curves of [Ru(phen)2(phen-btL)][PF6]2 (33) at various wavelengths with monoexponential fits shown in black and red.   Figure A1-5. Transient absorption difference spectrum of [Ru(phen-btL)3][PF6]2 (32) 200 ns after excitation at 450 nm (black) and 355 nm (red). 180   Figure A1-6. DPV - Reduction (top) and oxidation (bottom) of 200 M [Ru(phen-btL)3][PF6]2 (32) in CH3CN containing n-[Bu4N]PF6 (0.1 M) using a GC disk electrode (1 mm diameter). Voltammograms were obtained with two different negative potential limits. DPV parameters: Potential pulse amplitude = 0.05 V, step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V. 181   Figure A1-7. Comparison of  DPV for the electroreduction of [Ru(phen-btL)3][PF6]2 (32, red line) and [Ru(phen)3][PF6]2  (30, dashed blue line) in CH3CN containing n-[Bu4N]PF6 (0.1 M) using a Pt disk electrode (105 mm diameter). DPV parameters: Potential pulse amplitude = 0.05 V, step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V.   182   Figure A1-8. DPV - electroreduction (top) and electrooxidation (bottom) of [Ru(phen- tL)3][PF6]2 (32, 50 μM) in CH3CN containing 0.1 M n-[Bu4N]PF6 as supporting electrolyte and using a Pt disk electrode (1 mm diameter). DPV parameters: Potential pulse amplitude = 0.05 V. step size = 0.004 V, pulse duration = 0.05 s, pulse period = 0.2 V.  183   Figure A1-9. Absorption spectra recorded at selected potentials during the electroreduction of [Ru(phen)3][PF6]2 (30, 100 μM) in 0.1 M n-[Bu4N]PF6/CH3CN using progressively negative potentials from 0.0 V to -2.1 V. Working electrode: Pt mesh in capillary cell.  184   Figure A1-10. Difference absorbance spectra, A, during a linear potential cycle involving the electroreduction/electrooxidation of [Ru(tL)2(tatpp)][PF6]2 (64, 160 M) in CH3CN (0.1 M TBAPF6).  Spectra were collected during the negative-going potential scan (top frame) and the subsequent returning scan (bottom frame) at 5 mV/s in the +0.2 V to -1.1 V potential window.  ITO was used as working electrode and the electrochemical cell was a 4 mm quartz cuvette containing a Pt wire as counter electrode and a miniature Ag/AgCl (non-leak) reference electrode.     -0.2 -0.1 0.0 0.1   1000900800700600500400 Wavelength / nm -0.2 -0.1 0.0 0.1   1000900800700600500400 Wavelength / nm185  APPENDIX 2  Crystallography Data  Table A2-1. Selected crystal structure data for [Ru(bpy)2(tL)][PF6]2 (85) and [Ru(bpy)2(btL)][PF6]2 (86)  [Ru(tL)3][PF6]2▪1.5CH2Cl2 [Ru(btL)3][PF6]2▪2CH2Cl2 formula C38H28Cl0F12N6P2RuS2 C48H36Cl4F12N6P2RuS4 habit irregular, red plate, red dimensions / mm 0.75 × 0.22 × 0.10 0.36 × 0.24 × 0.04 temperature / K 90 90 cryst syst triclinic monoclinic space group P -1 P 21/c a / Å 11.372 (2) 19.9343 (17) b / Å 13.702 (3) 17.6009 (14) c / Å 16.258 (3) 15.8490 (13) α / ° 68.688 (3)  β / ° 71.222 (3) 108.735 (2) γ / ° 68.372 (4)  V / Å3 2141.6 (7) 5266.2 (8) Z 2 4 μ / mm-1 0.63 0.81 R[F2 > 2σ(F2)]a 0.047 0.085 Rw(F 2)a 0.116 0.207 goodness of fit 1.09 1.17 aFunction minimized by R =  ||Fo| - |Fc|| /  |Fo|, Rw = [ (w(Fo 2- Fc 2)2)/w(Fo 2)2]1/2.   186    Table A2-2. Selected crystal structure data for [Ru(bpy)2(sec-amL)][PF6]2 (87) and [Ru(bpy)2(tert-amL)][PF6]2 (88)  [Ru(sec-amL)3][PF6]2▪2CH3CN [Ru(tert-amL)3][PF6]2▪CH2Cl2 formula C44H36F12N10O2P2RuS2 C45H40Cl2F12N8O2P2RuS2 habit prism, red plate, red dimensions / mm 0.19 × 0.10 × 0.08 0.24 × 0.09 × 0.02 temperature / K 90 90 cryst syst triclinic monoclinic space group P -1 C 2/c a / Å 11.721 (3) 39.552 (6) b / Å 13.510 (3) 21.814 (4) c / Å 18.483 (4) 11.961 (2) α / ° 94.061 (4)  β / ° 98.273 (4) 99.822 (2) γ / ° 93.938 (4)  V / Å3 2880.0 (11) 10169 (3) Z 2 8 μ / mm-1 0.48 0.65 R[F2 > 2σ(F2)]a 0.087 0.069 Rw(F 2)a 0.259 0.200 goodness of fit 1.08 1.05 aFunction minimized by R =  ||Fo| - |Fc|| /  |Fo|, Rw = [ (w(Fo 2- Fc 2)2)/w(Fo 2)2]1/2.   

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