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Controlling electron transfer at sensitized TiO₂ surfaces Blair, Amber Dawn 2015

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	  CONTROLLING ELECTRON TRANSFER AT SENSITIZED TIO2 SURFACES   by  Amber Dawn Blair     B.Sc. Chemistry, Saint Mary’s University, 2012     A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF   MASTER OF SCIENCE   in   THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES  (Chemistry)     THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)    April 2015    © Amber Dawn Blair, 2015   	  Abstract  A series of three bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand with terminal triphenylamine (TPA) substituents have been synthesized and characterized for insight into electron transfer reactions at TiO2 surfaces. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(H3tctpy)] (pbpy = 6-phenyl-2,2’-bipyridine; H3tctpy = 4,4’,4”-tricarboxy-2,2’:6’,2”-terpyridine), where an electron-donating group (EDG) or an electron-withdrawing group (EWG) is installed about the anionic ring of the pbpy ligand and methyl groups surrounding the TPA-thiophene bridge. Modification of the anionic ring of the pbpy chelated with EDGs and EWGs enables the modulation of the Ru(III)/Ru(II) redox potential over 140 mV. This property offers the opportunity to turn on and off intramolecular hole transfer. Pulsed light laser excitation of the sensitized thin film resulted in rapid excited state injection and in some cases hole transfer to TPA [TiO2(e-)/Ru(III)−TPA → TiO2(e-)/Ru(II)−TPAŸ+]. The rate constants for charge recombination of [TiO2(e-)/Ru(III)−TPA → TiO2/Ru(II)−TPA and TiO2(e-)/Ru(II)−TPAŸ+ → TiO2/Ru(II)−TPA] were drastically affected by modification of the bridging unit and can be modulated over 5.2 – 6.2×105 s-1 and 1.7 – 5.1×104 s-1 respectively.   	  	  	  	  	  	  	  	  	  ii	  Preface  The work done in this thesis was done under the supervision of Dr. Curtis P. Berlinguette. Chapters 2, 3 and 4 are based on unpublished work. I synthesized the complexes in Chapters 2 and 4; performed the full characterization and all additional experiments. Chapter 3 is based on work done in collaboration with Prof. Gerald Meyer and the Meyer group at the University of North Carolina at Chapel Hill. Dr. Ke Hu performed the transient absorption and spectroelectrochemical experiments and I wrote the chapter.                                 	  iiiTable of Contents Abstract…………………………………………………………………………………… ii Preface…………………………………………………………………………………….iii Table of Contents………………………………………………………………………….iv List of Tables……………………………………………………………………………...vi List of Figures…………………………………………………………………………… vii List of Schemes…………………………………………………………………………. xiv List of Symbols and Abbreviations ……………………………………………………... xv Acknowledgements……………………………………………………………………. xviii  CHAPTER ONE: INTRODUCTION…………………………………………………….. 1  1.1. Solar Energy………………………………………………………………………... 1 1.2. Dye-Sensitized Solar Cells…………………………………………………………. 2 1.2.1. Principles of Operation of a DSSC………………………………………….3 1.2.2. Metal-Based Dyes in the DSSC……………………………………………. 5 1.2.3. Characterization Methods of a DSSC……………………………………… 7 1.3. Cycloruthenated Dyes for the DSSC……………………………………………….. 9 1.3.1. Bichromic Cycloruthenated Chromophores………………………………. 11 1.4. Intramolecular Hole Transfer………………………………………………………13 1.5. Project Objectives…………………………………………………………………. 15  CHAPTER TWO: SYNTHESIS AND STRUCTURAL CHARACTERIZATION……..19 2.1. Introduction………………………………………………………………………...19 2.2. Synthesis of Title Compounds…………………………………………………….. 26 2.3. Electrochemical Data……………………………………………………………… 34 2.4. Optical Properties…………………………………………………………………. 38 2.5. Computational Results…………………………………………………………….. 41 2.6. Summary…………………………………………………………………………... 44  CHAPTER THREE: INTERFACIAL ENERGETICS AND KINETICS………………. 46 3.1. Introduction………………………………………………………………………...46 3.2. Spectroelectrochemical Data……………………………………………………… 49 3.3. Transient Absorption Spectroscopy……………………………………………….. 58 3.4. Summary…………………………………………………………………………... 67  CHAPTER FOUR: CONCLUSIONS AND FUTURE DIRECTIONS…………………. 68 4.1. Conclusions………………………………………………………………………...68 4.2. Future Directions…………………………………………………………………...69  CHAPTER FIVE: EXPERIMENTAL…………………………………………………... 73 5.1. Chapter 2…………………………………………………………………………... 73 5.2. Chapter 3…………………………………………………………………………... 92  REFERENCES…………………………………………………………………………... 94 	  iv	  APPENDIX A: SPECTRAL DATA…………………………………………………… 100  APPENDIX B: GAUSSIAN DATA…………………………………………………… 137  APPENDIX C: ATTEMPTED SYNTHESIS………………………………………….. 147                                          v	  List of Tables  Table 1.1. Designation of Compoundsa…………………………………………......18  Table 2.1. Summary of Spectroscopic and Electrochemical Properties of Ligands L1-L4 and Complexes 2, 4, 8…………………………………………………......................36  Table 3.1. Formal Reduction Potentials of Ru(III)/Ru(II) and TPA•+/TPA0 for Complexes 2, 4, and 8 on TiO2 in 0.5 M LiClO4 CH3CN……………………………….57  Table. 3.2. Charge Recombination Rate Constants of 2/TiO2, 4/TiO2, and 8/TiO2 in 0.5 M LiClO4/CH3CN by KWW Fitting…………………………………………………64  Table 3.3. Calculated and Measured Quasi-Equilibrium Constants at 25 ns Time Delay and Intramolecular Hole Transfer Quantum Yields (Φ) of Complexes on TiO2 in 0.5 M LiClO4/CH3CN after 532 nm Light Excitation………………………...................65  Table B.1.  Optimized Cartesian Coordinates for (2)……………………………….137  Table B.2.  Optimized Cartesian Coordinates for (4)……………………………….140     Table B.3.  Optimized Cartesian Coordinates for (8)……………………………….143  Table B.4.  Potential Energy Scan for (2) About the Dihedral Angle Between Atoms S58, C61, C63, and C65………………………………………………………………..146  Table C.1. Optimization of the synthesis of P3…………………………………….157                    vi	  List of Figures   Figure 1.1. Schematic of a conventional DSSC with labeled components and approximate dimensions…………………………………………………………………..4  Figure 1.2. Summary of select absorption/emission events and charge transfer/transport processes in the DSSC. S = sensitizer; S* = photo-excited sensitizer; A = light absorption; kinj = rate of charge-injection into TiO2 nanoparticle; kCT = rate of charge transport through mesoporous TiO2 layer; kER = rate of electrolyte (i.e., I3-) reduction; kreg = rate of dye regeneration by I-; krec1 = rate of charge recombination between electron in the conduction band (ECB) of TiO2 and I3-; krec2 = rate of charge recombination between electron in ECB of TiO2 and the photo-oxidized dye (S+); kdecay = rate of radiative decay of S*; Ef = Fermi level energy; Evb = valence band energy…………………………………...............................................................................5  Figure 1.3. Chemical structures of select DSSC dyes that have been documented to produce a PCE > 10% in the DSSC. The N3 dye is highlighted by the enclosure. Sample codes correspond those in the original reports. (aDoubly deprotonated form of N3; bA proton replaced by the Na+ cation; cProtons are replaced by Na+ and NBu4+ cations.)…...7  Figure 1.4. Photocurrent density-voltage curve (blue trace) and the corresponding power density curve (grey trace). Jsc = short-circuit current density; Voc = the open circuit voltage; FF = the fill factor; Vm = maximum open circuit voltage; Jm = maximum short circuit current density; Pmax = maximum power point…………………………………….8  Figure 1.5. Bichromic cyclometalated ruthenium(II) sensitizers with electron donating groups (EDGs) and electron withdrawing groups (EWGs ) positioned at –R1 and –R2/–R3………………………………………………………………………………………...12  Figure 1.6. Excited-state electron injection and intramolecular hole transfer for a sensitizer-linker-donor compound anchored on a TiO2 surface…………………………14  Figure 1.7. Structural formulae for the set of ruthenium(II)/osmium(II) bis(2,2’:6’,2”-terpyridine) binuclear complexes………………………………………………………...16  Figure 1.8. Optimization of ruthenium-based dyads for the DSSC. Methyl groups about the bridging unit disrupt conjugation to decrease electronic communication between the TPA and metal-center to decrease the rate of interfacial recombination. Modification of –R1 and –R2 modulates the energy of the HOMO positioning it on the metal or the TPA unit.…………………………………………………............................17  Figure 2.1. Select bis-tridentate cycloruthenated complexes and their corresponding extinction coefficients……………………………………………………………………20   vii	  Figure 2.2. Thermodynamic positions of the frontier molecular orbitals of a) R1/R2 = H, R3 = OMe and b) R1 = -OMe, R2 = CF3, R3 = H relative to the conduction band (ECB) of TiO2 and the I-/I3- redox couple. The relative positions of the energy levels for b) are conducive to shuttling electrons towards the TiO2 and holes towards the terminal TPA unit. The energy levels for a) should not, in principle, accommodate this same effect….22  Figure 2.3. Hole transfer processes indicating a) no hole transfer to yield TPA-Ru(III)/TiO2(e-); b) partial hole transfer; and c) hole transfer to yield Ru(II)/TiO2(e-)….23  Figure 2.4. Optimization of ruthenium-based dyads for the DSSC. The addition of methyl groups about the bridging unit influences the dihedral angle between the TPA and thiophene. ………………………………………………………………………………..24  Figure 2.5. Numbering scheme for representative bichromic cyclometalated ruthenium(II) sensitizers with EDGs/EWGs positioned at –R1/−R2…………………….25  Figure 2.6. 1H NMR spectra for CDCl3 solutions of 2, 4 and 8 at ambient temperatures highlighting how substituents affect the electron density on the anionic ring. Color scheme: green, Hq; orange, Ho; blue, Hp; red, Hn………………………………………..32  Figure 2.7. Cyclic voltammograms for ligand L1 and the corresponding carboxylic acid metal complex 2 in CH2Cl2 at ambient temperatures (scan rate = 100 mV/s). Dashed lines emphasize that Ep,a and Ep,c of the TPAŸ+ /TPAO couple are the same as those for the free ligand and complex………………………………………………………………….38  Figure 2.8. UV-vis absorption spectra demonstrating the optical response to the substituents at the pbpy chelate (e.g., 2, R1/R2= -H; 4, R1 = -CF3, R2 = -H; 8, R1 = -H, R2 = -OMe)………………………………………………………………………………….40  Figure 2.9. UV-vis spectra collected in MeOH at ambient temperature of 4 (red trace) and the conjugated counterpart (black trace)…………………………………………….41  Figure 2.10. Summary of DFT results for 2, 4, and 8. H atoms omitted for clarity…...42  Figure 2.11. Atom labels for complex 2. Blue area highlighted for calculated dihedral angle……………………………………………………………………………………...43  Figure 2.12.  Potential energy for rotation about the dihedral angle of atoms S58, C61, C63 and C65 in complex 2……………………………………………………………….44  Figure 3.1. Listing of representative dyad molecules capable of intramolecular hole transfer: a) [Ru(dcbH2)2(4-CH3,4’-CH2-PTZ,-2,2’-bipyridine))]2+ (PTZ = phenothiazine); b) [Ru(TPA-tpy)(tpyPO3H2)].……………………………………………………………46  Figure 3.2. Designation of compounds. Counterion = NO3- for 8, 2, and 4………….47  viii	  Figure 3.3. Excited-state electron injection and intramolecular hole transfer for a sensitizer-linker-donor compound anchored on a TiO2 surface…………………………48  Figure 3.4. UV-vis-NIR absorption spectra of (a) 2/TiO2 and (c) 4/TiO2 and (e) 8/TiO2 measured at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions. UV-vis-NIR absorption difference spectra of (b) 2/TiO2 and (d) 4/TiO2 and (f) 8/TiO2…………………………………………………………………………………….50  Figure 3.5. Initial oxidation absorbance difference spectrum 8/TiO2 measured at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions. Circled in red is the set of isosbestic points………………………………………………………………………….52  Figure 3.6. UV-vis-NIR absorption difference spectra of 8/TiO2 at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions……………………………………………53  Figure 3.7. The UV-vis absorption of (a) 8/TiO2, (b) 2/TiO2, or (c) 4/TiO2 in 0.5 M LiClO4/CH3CN in the 2/TiO2, 4/TiO2, or 8/TiO2 (black); 2+/TiO2, 4+/TiO2, or 8+/TiO2 (red), and 22+/TiO2, 42+/TiO2, or 82+/TiO2 (blue) states. Note that the Ru(II)-NAr3 and Ru(III)-NAr3+ states are mathematically calculated……………………………………..54  Figure 3.8. The density of states calculations show the fraction (x) of dye molecules of (a) 2/TiO2, (b) 4/TiO2, or (c) 8/TiO2 present in the 2/TiO2, 4/TiO2, or 8/TiO2 (black solid squares), 2+/TiO2, 4+/TiO2, or 8+/TiO2 (red solid circles), and 22+/TiO2, 42+/TiO2, or 82+/TiO2 (green solid triangles) states……………………………………………………55  Figure 3.9. Absorption difference spectra measured at indicated time delays after pulsed 532 nm laser light excitation (laser irradiance: 1.0 mJ/pulse) of (a) 8/TiO2, (b) 2/TiO2, or (c) 4/TiO2 immersed in 0.5 M LiClO4/CH3CN solution……………………...59  Figure 3.10. Decay associated spectra of Ru(II)-NAr3Ÿ+ for a) 8/TiO2 c) 2/TiO2 and Ru(III)-NAr3 for e) 4/TiO2. The standard decay associated spectra of Ru(III)-NAr3 for b) 8/TiO2 d) 2/TiO2 and Ru(II)-NAr3Ÿ+ for f) 4/TiO2. All sensitized thin films were immersed in 0.5 M LiClO4/CH3CN solution…………………………………….………61  Figure 3.11. The normalized species associated kinetics at 510 nm and 750 nm in a linear time scale representing charge recombination of Ru(III)-NAr3/TiO2(e-) à Ru(II)-NAr3/TiO2 and Ru(II)-NAr3Ÿ+/TiO2(e-) à Ru(II)-NAr3/TiO2 respectively in a) 8/TiO2 c) 2/TiO2 and e) 4/TiO2 after 532 nm laser light excitation (laser irradiance: 1.0 mJ/pulse). Show the same normalized kinetics in a log time scale of b) 8/TiO2, d) 2/TiO2 and f) 4/TiO2. Overlaid on a-f in yellow are KWW fits with a shared beta value of 0.19……...63  Figure 3.12. Fractions of Ru(III)-NAr3, Ru(II)-NAr3Ÿ+, and Ru(II)-NAr3 as a function of time delays. The insets show the early time scale up to 500 ns………………………….66  ix	  Figure 4.1. Molecular structures of a series of bichromic cycloruthenated complexes with modified spacer units to study interfacial recombination of TiO2 electrons and the oxidized dye. In all cases the HOMO should be localized to the TPA unit……………..70  Figure 4.2. Proposed bichromic cycloruthenated sensitizer for a photoelectrosynthesis cell………………………………………………………………………………………..71  Figure 4.3. Proposed mechanism for a bichromic cycloruthenated sensitizer in a photoelectrosynthesis cell………………………………………………………………..72  Figure 5.1.  Labeling scheme for 1H NMR signal assignments………………………75  Figure A.1. N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (P1). 1H NMR (300 MHz, CDCl3, 298K)…………………………………………………………………………...101  Figure A.2. N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (P1). 13C NMR (100 MHz, CDCl3, 298K)…………………………………………………………………………...102  Figure A.3. 4-Bromo-N,N-bis(4-methoxyphenyl)3,5-dimethylaniline (P2). 1H NMR (300 MHz, CDCl3, 298K)………………………………………………………………103  Figure A.4. 4-Bromo-N,N-bis(4-methoxyphenyl)3,5-dimethylaniline (P2). 13C NMR (100 MHz, CDCl3, 298K)………………………………………………………………104  Figure A.5. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine (P6). 1H NMR (300 MHz, CDCl3, 298K)…………………………………..105  Figure A.6. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine (P6). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………………………………………...106  Figure A.7. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine (P6). 13C NMR (100 MHz, CDCl3, 298K)………………………………….107  Figure A.8. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine (P6). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………………………………………...108  Figure A.9. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L1). 1H NMR (300 MHz, CDCl3, 298K)……………………109  Figure A.10. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L1). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………………………………………...110  x	  Figure A.11. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L1). 13C NMR (100 MHz, CDCl3, 298K)…………………...111  Figure A.12. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L1). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………………………………112  Figure A.13. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L2). 1H NMR (300 MHz, CDCl3, 298K)……………………………………………………………………113  Figure A.14. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L2). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region……………………………………114  Figure A.15. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L2). 13C NMR (100 MHz, CDCl3, 298K)……………………………………………………………………115  Figure A.16. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L2). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region……………………………………116  Figure A.17. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 1H NMR (300 MHz, CDCl3, 298K)…………………………………………………………………………………...117  Figure A.18. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………..118  Figure A.19. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 13C NMR (100 MHz, CDCl3, 298K)…………………………………………………………………………………...119  Figure A.20. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………..120  Figure A.21. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline  (L4). 1H NMR (300 MHz, CDCl3, 298K)…………………………….121  Figure A.22. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline  (L4). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region...............................................................................................................................122  xi	  Figure A.23. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline  (L4). 13C NMR (100 MHz, CDCl3, 298K)…………………………...123  Figure A.24. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline  (L4). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region…………………………………………………………………………………...124  Figure A.25. [Ru(L1)(L5)] (2). 1H NMR (300 MHz, MeOD, 298K)………………...125  Figure A.26. [Ru(L1)(L5)] (2). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region…………………………………………………………………………126  Figure A.27. [Ru(L2)(L5)] (4). 1H NMR (300 MHz, MeOD, 298K)………………...127  Figure A.28. [Ru(L2)(L5)] (4). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region…………………………………………………………………………128  Figure A.29. [Ru(L4)(L5)] (8). 1H NMR (300 MHz, MeOD, 298K)………………...129  Figure A.30. [Ru(L4)(L5)] (8). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region…………………………………………………………………………130  Figure A.31. UV-vis absorption spectra of ligand L1 in MeOH where R1, R2 = −H...131  Figure A.32. UV-vis absorption spectra of ligand L2 in MeOH where R1 = −CF3, R2 = −H………………………………………………………………………………………131  Figure A.33. UV-vis absorption spectra of ligand L3 in MeOH where R1 = −CF3, R2 = −CF3…………………………………………………………………………………….132  Figure A.34. UV-vis absorption spectra of ligand L4 in MeOH where R1 = −H, R2 = −OMe…………………………………………………………………………………...132  Figure A.35. UV-vis absorption spectra of ligands in MeOH demonstrating minor optical changes when R1, R2 = −H (L1), R1 = −CF3, R2 = −H (L2), R1 = −CF3, R2 = −CF3 (L3) and R1 = −H, R2 = −OMe (L4)……………………………………………………133  Figure A.36. Cyclic voltammogram of ligand L1 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………133  Figure A.37. Cyclic voltammogram of ligand L2 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………134  Figure A.38. Cyclic voltammogram of ligand L3 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………134  xii	  Figure A.39. Cyclic voltammogram of ligand L4 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………135  Figure A.40. Cyclic voltammogram of complex 2 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………135  Figure A.41. Cyclic voltammogram of complex 4 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)……………………………………………………………………136  Figure A.42. Cyclic voltammogram of ligand 8 in CH2Cl2 at ambient temperature (scan rate 100 mV/s)…………………………………………………………………………..136  Figure C.1. Attempted lithiation of P2 using trimethylborate………………………147  Figure C.2. Attempted lithiation of P2 using triisopropylborate……………………148  Figure C.3. Attempted lithiation of P2 using trimethylborate………………………148  Figure C.4. Attempted lithiation of P2 using 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane…………………………………………………………………………...149  Figure C.5. Attempted borylation of P2 using a palladium catalyst………………...150  Figure C.6. Attempted lithiation of 6-phenyl-4-(thiophen-2-yl)-2,2’-bipyridine using trimethylborate………………………………………………………………………….151  Figure C.7. Attempted cyclometalation of L3………………………………………152  Figure C.8. Attempted cyclometalation of L3………………………………………153  Figure C.9. Attempted cyclometalation of P6………………………………………154  Figure C.10. Attempted Suzuki cross-coupling of [Ru(P6)(L5)]NO3 and P3....…......154 Figure C.11. Experimental conditions for the Miyaura borylation…………………...157            xiii	  List of Schemes  Scheme 2.1. Synthesis of Precursors P1-P2.………………………………………….. 27  Scheme 2.2. Synthesis of Precursor P3………………………………………………... 27 Scheme 2.3. Synthesis of Precursors P4-P7.…………………………………………...28  Scheme 2.4. Synthesis of Ligands L1-L4……………………………………………... 29  Scheme 2.5. Assembly of Complexes 1, 3, 5, and 7…………………………………... 30  Scheme 2.6. Assembly of Complexes 2, 4, 6, and 8…………………………………... 31  Scheme 3.1. The Interfacial Redox Equilibrium Under Study………………………... 48                                xiv	  List of Symbols and Abbreviations   Symbol Definition °C K - + Ÿ a A Al2O3 AM1.5 Anal. Calcd. APCE bpy C^N C^N^N calcd. CDCl3 CD3OD CO2Me COSY CV d D-A DCM dcbpy DFT DMF DMSO DOS DPV D-π-A DSSC E E1/2 EA ECB ESI EDG Ef Et2O EtOAc EtOH EWG Eq.  degree Celcius Kelvin anion cation radical ideality factor light absorption aluminum(III) oxide Air Mass 1.5 solar spectrum calculate (elemental) analysis absorbed photon to current efficiency 2,2’-bipyridine cyclometalating bidentate ligand cyclometalating tridentate ligand (C and N denote coordinating atoms) calculated deuterated chloroform deuterated methanol methyl ester correlation spectroscopy cyclic voltammetry doublet donor-acceptor dichloromethane 4,4’-dicarboxy-2,2’-bipyridine density functional theory N,N’-dimethylformamide dimethylsulfoxide density of states differential pulse voltammetry donor-bridge-acceptor dye-sensitized solar cell energy mid-point of Ep,a and Ep,a elemental analysis conduction band energy electrospray ionization electron-donating group Fermi level energy diethyl ether ethyl acetate ethanol electron-withdrawing group equation xv	  eq. eV Evb Fc Fc+ FF FTO GS h H3tctpy HOMO I-V ILCT Jmax Jsc J-V Imax IPCE k kcr kCT kdecay kER kinj krec1 krec2 kreg KWW L LANL2DZ LR LUMO m MALDI-TOF Me MeCN MeOH MLCT MO2 MS N^C^N N^N^N NBS nBuLi NCS Nd:YAG equivalent electron volts valence band energy Ferrocene Ferrocenium fill factor fluorine-doped tin oxide ground state hour 4,4’,4”-tricarboxy-2,2’:6’2”-terpyridine highest occupied molecular orbital current-voltage intra-ligand charge-transfer current density at the maximum power point short-circuit density current density-voltage current at the maximum power point incident photon-to-current efficiency rate constant charge recombination rate constant rate of charge transport through TiO2 layer rate of radiative decay of S* rate of electrolyte (i.e., I3-) reduction rate of charge-injection into TiO2 nanoparticle rate of charge recombination between an e- in the ECB of TiO2 and I3- rate of charge recombination between an e- in the ECB of TiO2 and S+ rate of dye regeneration by I- Kohlraush-Williams-Watts liter Los Alamos National Laboratory 2-double-z  low resolution lowest unoccupied molecular orbital multiplet matrix assisted laser desorption ionization time of flight methyl acetonitrile methanol metal-to-ligand charge transfer metal oxide mass spectrometry cyclometalating tridentate ligand (C and N denote coordinating atoms) tridentate polypyridyl ligand (N denotes coordinating atoms) N-bromosuccinimide n-butyllithium isothiocyanate neodymium-doped yttrium aluminum garnet xvi	  NEt3 NHE NMR OMe pbpy PCE Pin Pmax ppm ppy PV Rf RT S S+ S* sat. SiO2 t t1/2 TA TCO TD-DFT THF TiO2 TiO2(e-) TPA tpy Vmax Voc V β ε δ Δ η λ λem λex λmax µmol Φ Ω φ triethylamine normal hydrogen electrode nuclear magnetic resonance methoxy 6-phenyl-2,2’-bipyridine power conversion efficiency incident power of illumination maximum power point parts per million 2-phenyl pyridine photovoltaic retention factor room temperature sensitizer photo-oxidized sensitizer excited sensitizer saturated silica triplet half-life transient absorption transparent conductive oxide time dependent density functional theory tetrahydrofuran titanium dioxide electrons in TiO2 triphenylamine 2,2’:6’2”-terpyridine voltage at maximum power point open-circuit voltage distribution parameter volt molar extinction coefficient chemical shift difference power conversion efficiency wavelength (nm) emission maximum excitation wavelength absorption maximum micromole quantum yield resistance (ohms) dihedral angle  	  xvii	  Acknowledgements  First, I would like to thank my supervisor Dr. Curtis P. Berlinguette for the opportunity to conduct research and learn in his research group. Your enthusiasm, drive and work ethic were strong contributors to the successful completion of this thesis.  Thank you to my defense committee members Dr. Sarah Burke and Dr. Mark MacLachlan for their time and critical analysis of my work.  I would like to thank the many Berlinguette group members, past and present, in Calgary and in British Columbia, with whom I’ve had the pleasure of working alongside. I would like to give special thanks to Dr. Phil Schauer and Dr. Matthew DeWit for providing immense synthetic guidance and mentorship. The imput and guidance I have received from these men have been immeasurable and I am truly grateful to have had such amazing mentors.  At the University of North Carolina I would like to thank Prof. Gerald Meyer and Ke Hu for studying the electron-transfer events of the bichromic cycloruthenated sensitizers at the TiO2 surface.  My time in both Calgary and British Columbia would not have been the same without the many friendships that I have enjoyed and I thank those who have been there as you have undoubtedly kept me sane. A special mention must be given out to Eric Bowes his time and energy spent providing critical thought and always an available ear as well as providing a warm and fun distraction from work.  Last, but definitely not least, I thank my family for their continued love and support. Despite being on opposite ends of the country, it was always great to hear their voices. I would not be where I am today without their unwavering encouragement. xviii	  CHAPTER ONE: INTRODUCTION 1.1. Solar Energy  Nobel laureate Richard Smalley has identified energy and environment as two of the grand challenges facing humanity over the next fifty years. The energy challenge is imminent as the world’s demand for energy is projected to double by 2050 and more than triple by the end of the century.1 An abundant supply of energy is necessary for global economic and environmental stability. A review produced by the British Petroleum Group states that 87% of the world’s energy is derived from the consumption of fossil fuels, with roughly equal contributions from oil, coal and natural gas.2 The increase in consumption of non-renewable forms of energy has caused growing concern that the production of oil will soon be unable to meet the increasing demand.3 In addition, the combustion exhaust of fossil fuels has been implicated in anthropogenic greenhouse gas emissions, which are predicted to produce widespread environmental damage.4 The threat of climate change imposes a second requirement on prospective energy resources in that they must produce energy without the emission of additional greenhouse gases. Leading us to one of society’s largest challenges: finding sufficient supplies of clean energy for the future. Solar energy is a vast and virtually inexhaustible resource. More energy from sunlight strikes the Earth in one hour (4.3 × 1020 J) than all the energy consumed on the planet in a year (4.1 × 1020 J).1 Covering only 0.1% of the earth’s surface with solar cells producing an efficiency of 10% would be able to satisfy global demand.5 Thus, making solar energy the largest single source of clean energy that is readily available.  While technologies have been developed to harness solar energy efficiently, they are not yet an economically viable alternative to fossil fuels.6 Only 2% of the global energy market is1	  derived from renewable resources (including wind, geothermal, solar, biomass and waste).2 Solar electric power production generated by photovoltaic devices constitutes a tiny fraction (about 0.03%) of the world’s energy needs, but is experiencing a rapid growth rate. In 2013 power generation increased by 33% from 0.18% to 0.24% of global energy consumption.2,7 The abundant supply of solar energy makes the efficient and cost-effective conversion of solar radiation to electricity a compelling scientific goal.   1.2. Dye-Sensitized Solar Cells  The current global market for photovoltaic (PV) devices has been dominated by solid-state junction devices typically composed of crystalline or amorphous silicon. The current form of technology includes high manufacturing costs due to the need for highly purified silicon for devices, and high processing temperatures.8 Dye sensitized solar cells (DSSCs) have attracted much attention owing to their ease of fabrication, cost effectiveness and high efficiency of solar energy conversion.9 The seminal paper on DSSCs was reported in 1991 wherein O’Reagan and Grätzel described the creation of a DSSC that produced a power conversion efficiency (PCE) of 7.1%.10 Subsequent work by the Grätzel program quickly pushed the efficiency to 10%.11 Their discovery spawned a renewed interest in the sensitization of semiconductors and created an economically viable PV technology. The cells use a mesoporous semiconductor electrode that has a high internal surface area leading to a larger number of dye molecules that can be adsorbed directly on the surface, increasing the number of incident photons that can be absorbed per area.12 Given the inherent intermittent nature of solar irradiation, DSSCs offer better performance under diffuse and indirect light conditions.12 They also offer the prospect to design solar cells with a large flexibility in color, shape and transparency.12 2	  1.2.1 Principles of Operation of a DSSC  In DSSC devices, the anode is composed of a transparent conductive substrate (e.g., fluorine-doped tin oxide (FTO)), and a wide band gap semiconductor. The most common semiconductor is TiO2,13 although alternative wide band gap semiconductors such as ZnO,14-17 Nb2O518,19 and other oxides20,21 have also been used.  The photoanode is composed of a ~12 µm thick film of transparent 10-20 nm diameter TiO2 nanoparticles.3 The nanoparticles are often covered with a ~4 µm thick film of ~400 nm diameter TiO2 particles.3 The larger nanoparticles act as a scattering layer to increase the optical path length of light thereby increasing the probability of absorption of the photon by the dye.5,22 A monolayer of sensitizer is covalently bound to the TiO2 surface via anchoring groups. Carboxylate anchors are the most commonly used anchoring groups,12 although phosphonate,23-25 hydroxamate,26-29 catecholate30,31 and others32-35 have been explored (Figure 1.1). The cathode is typically a TCO (transparent conductive oxide) substrate coated with platinum to catalyze the reduction of the oxidized electrolyte. The anode and the cathode are separated by a thermoplastic sealant, which serves to separate the two electrodes and to encapsulate the liquid electrolyte. The liquid electrolyte, typically utilizes an I3-/I- redox couple in a volatile organic solvent (e.g., CH3CN).12 The iodine/iodine based electrolyte solution serves as an electron shuttle to reduce the oxidized sensitizer by an intermolecular electron transfer. Efforts have been made to use different redox couples, where the world record PCE for a DSSC is now 13.0 % with a cobalt (III/II) redox shuttle.36  3	    Figure 1.1. Schematic of a conventional DSSC with labeled components and approximate dimensions.   Fundamental to the DSSC is the sensitization of a semiconductor by a dye molecule to achieve efficient charge separation (Figure 1.1). Upon light absorption by the sensitizer (S, Figure 1.2) an electron is promoted from the ground state to an excited state (S*, Figure 1.2).  Following light absorption, the excited dye rapidly injects an electron into the conduction band (Ecb) of TiO2. The injected electrons diffuse through the particle network through a ‘random walk’ to be collected at the transparent conducting oxide electrode. The original state of the dye is restored by electron donation from the electrolyte. The oxidized electrolyte is regenerated in turn by the reduction at the counter 4	  electrode via electron migration through the external load to complete the circuit (Figure 1.2).   Figure 1.2. Summary of select absorption/emission events and charge transfer/transport processes in the DSSC. S = sensitizer; S* = photo-excited sensitizer; A = light absorption; kinj = rate of charge-injection into TiO2 nanoparticle; kCT = rate of charge transport through mesoporous TiO2 layer; kER = rate of electrolyte (i.e., I3-) reduction; kreg = rate of dye regeneration by I-; krec1 = rate of charge recombination between electron in the conduction band (ECB) of TiO2 and I3-; krec2 = rate of charge recombination between electron in ECB of TiO2 and the photo-oxidized dye (S+); kdecay = rate of radiative decay of S*; Ef = Fermi level energy; Evb = valence band energy.   1.2.2. Metal-Based Dyes in the DSSC  The molecular structure of the dye plays an important role in the DSSCs. After absorption of light, efficient charge separation of holes and electrons must occur, and the respective charges must separate and flow through an external circuit to do electrical work before recombination. A dye should absorb incident photons broadly within the 5	  visible region absorbing the majority of incident photons with wavelengths shorter than 900 nm, with a high absorptivity to enable the use of thinner TiO2 layers. The dye must also contain anchoring groups to covalently bind to the TiO2 surface. For efficient electron injection into the anode, the lowest occupied molecular orbital (LUMO) of the dye should be localized near the anchoring group to facilitate efficient electron injection into the conduction band of the TiO2. The energy of the lowest excited state must be sufficiently negatively shifted relative to the conduction band of TiO2 at -0.5 V versus the normal hydrogen electrode (NHE) and the highest occupied molecular orbital (HOMO) must be positively shifted relative to the redox couple (with an I3-/I- electrolyte, the HOMO must be more positive than +0.8 V)37 to facilitate efficient regeneration.  Finally, the sensitizer needs to be photochemically, thermally and electrochemically robust within an operating DSSC. The most thoroughly studied, and generally the best performing dyes in the literature, are derivatives of [Ru(dcbpy)2(NCS)2] (N3: dcbpy = 4,4’-dicarboxy-2,2’-bipyridine), which is the first “champion” dye (i.e., dyes that have surpassed the 10% PCE in the DSSC).11 Champion dyes widely studied and closely related to N3 include the tetrabutylammonium salt of N3, (Bu4N)2[Ru(4-carboxy,4’-carboxylato-2,2’-bipyridine)2(NCS)2] (N719) and the black dye,38 (Bu4N)[Ru(4,4’,4”-tricarboxy,2,2’:6’,2”-terpyridine)(NCS)3] with an efficiency of 11.4%.39 A number of notable dyes that have since deviated from the N3 motif have been able to break the 10% PCE threshold (Figure 1.3), with a landmark discovery in 2014 made by Mathew, Yella, Grätzel, and coworkers who reported a zinc porphyrin that could achieve 13% PCE in the DSSC.36 6	  	  	  Figure 1.3. Chemical structures of select DSSC dyes that have been documented to produce a PCE > 10% in the DSSC. The N3 dye is highlighted by the enclosure. Sample codes correspond those in the original reports. (aDoubly deprotonated form of N3; bA proton replaced by the Na+ cation; cProtons are replaced by Na+ and NBu4+ cations).    1.2.3. Characterization Methods of a DSSC  The primary characterization method of a DSSC is measuring the current-voltage (I-V) characteristics of a solar cell40, which are used to determine the power conversion efficiency (PCE), η, the incident photon to current efficiency (IPCE) and the absorbed photon to current efficiency (APCE). 7	  To produce light similar to that incident on Earth’s surface, a solar simulator is used to apply a wide range of voltages and the current output is recorded. The applied bias voltage generates an opposing current to that of the photogenerated current. The result is an I-V curve, which after normalization for the active area of the PV material becomes a current density voltage (J-V) curve (Figure 1.4.).    Figure 1.4. Photocurrent density-voltage curve (blue trace) and the corresponding power density curve (grey trace). Jsc = short-circuit current density; Voc = the open circuit voltage; FF =  the fill factor; Vm = maximum open circuit voltage; Jm = maximum short circuit current density; Pmax = maximum power point.   The overall solar conversion efficiency (equation 1) is the ratio of the product of the short-circuit current density, Jsc, the open-circuit photovoltage, Voc and the fill factor (equation 2), FF, where Pin is the total solar power incident on the cell (usually 100 mW cm-2 for air mass (AM) 1.5).                                                                                                                    (1)  8	                                                                                                                 (2)  Another important characterization technique is the IPCE (equation 3), which measures the number of electrons generated relative to incident monochromatic light and denotes the fraction of incident light that is converted to current. Information from the IPCE can be related to the absorption profile of the sensitizer and provides a key comparison to other dyes.                                                                                               (3)              From a fundamental viewpoint, the absorbed photon to current conversion efficiency (APCE) describes how efficient the number of the absorbed photons are converted into current.12 The APCE is obtained by dividing the IPCE number by the light harvesting efficiency (LHE).    1.3. Cycloruthenated Dyes for the DSSC  The current set of commercially relevant dyes (e.g., N3, N719, black dye) are susceptible to degradation over time due to in part the loss of the monodentate labile NCS- ligands.41 In recognition of these shortcomings the Berlinguette program, and others, have sought to replace the isothiocyanate ligands with chelating multidentate cyclometalating ligands without compromising device performance.13,42-44 The first example of a cycloruthenated sensitizer on TiO2 was reported by van Koten et al., where they synthesized tridentate ruthenium(II) complexes of the general formula [Ru(II)(N^N^N)(N^N^C)]+1 to produce a modest PCE.45 The Berlinguette group had synthesized a series of tris-bidentate [Ru(bpy)2(ppy)]+ (ppy = 2-phenyl pyridine) complexes to elucidate the electronic structure of these dyes. The phenyl ring was 9	  systematically modified to demonstrate exquisite control of the energetics of the HOMO for ruthenium-based DSSC sensitizers.46 The effectiveness of the cycloruthenated motif as a molecular platform was shown in 2009 by Grätzel et al., generating an η value of 10.1% in a DSSC with the tris-bidentate cyclometalated complex [Ru(dcbpyH2)2(ppyF2)]+ (ppyF2 = 2-(2,4-difluorophenyl)pyridine).47   One of the unique advantages of this class of dyes allows for control of the energy of the HOMO through modifications of the substituents of the anionic ring.46 This strategy is beneficial because direct control of the HOMO energy level on dyes containing isothiocyanate ligands would require potentially challenging chemical alteration of the NCS- ligand. While on complexes containing an anionic ring, the installation of electron-donating or -withdrawing groups on the phenyl ring can lower or increase respectively, the metal-based oxidation potential.46   There are numerous champion ruthenium-based sensitizers bearing bidentate ligands that have been established.13,37 Given the myriad of polypyridyl ruthenium complexes that have been documented it may be considered surprising that those with tridentate ligands are far less pervasive in the literature. The black dye held the highest PCE measured for a DSSC at 11.4%39 until only recently.48 Despite this achievement the black dye stood as the only champion dye bearing a tridentate ligand. Many derivatives of [Ru(tpy)2]2+ (tpy = 2,2’;6’2”-terpyridine), aside from the black dye only exhibit a DSSC efficiency in excess of ca. 2%.13 This observation is primarily attributed to inferior spectral coverage and more accessible excited state deactivation pathways, due to a lack of separation between the 3MLCT and 3MC states.44,49 The Berlinguette program has therefore pursued strategies to enhance the light-harvesting properties of complexes 10	  bearing tridentate ligands. Exploiting the wealth of knowledge of ruthenium photochemistry, a dramatic enhancement in the light harvesting properties could be achieved by increasing the transition dipole moment.44 The next section describes exploiting this strategy of using donor-acceptor (D-A) chemistry to make even better chromophores.   1.3.1. Bichromic cycloruthenated chromophores  Higher molar extinction coefficient (ε) values would be beneficial for applications in the DSSC as more strongly absorbing dyes can enable the use of thinner TiO2 films, thereby reducing the overall cost.50 Organic chromophores designed for the DSSC often contain a D-π-A motif, an arrangement that facilitates intramolecular π-π* transitions offering large molar extinction coefficients as well as exhibiting conversion efficiencies over 10%.51-54 While ε values are typically lower for ruthenium(II) polypyridyl based dyes relative to their organic counterparts, the absorption profiles of the metal complexes are generally broader and are extended to longer wavelengths, giving them greater utility in solar energy conversion schemes.5 These observations prompted the Berlinguette program to explore the effects of appending a secondary organic chromophore, a triphenylamine (TPA) group, to bis-tridentate cyclometalated ruthenium complexes.55-59  Among the metal-free organic dyes TPA and derivatives as donor units have displayed promising properties in the development of photovoltaic devices due to their excellent light absorption properties and ease of modification.60 The first dye for the DSSC bearing a TPA moiety was documented by Sun and Hagfeldt,61 while a successive study was done by Wang et al. reaching a remarkable efficiency of 10.2%.53 The attachment of a TPA unit to a metal scaffold has also been reported by several groups.62-11	  64 These assemblies also serve as a secondary redox-active unit that has been shown to suppress recombination through the production of long-lived charge separation between the conduction band electrons and the oxidized sensitizer in polypyridyl ruthenium sensitizers.65-67 These studies led the Berlinguette group to build a library of bichromic ruthenium dyes that exploit the properties of both the TPA and anionic chelate as shown in Figure 1.5.56,57     Figure 1.5. Bichromic cyclometalated ruthenium(II) sensitizers with electron donating groups (EDGs) and electron withdrawing groups (EWGs ) positioned at –R1 and –R2/–R3.    The information derived from the library of bichromic cyclometalated ruthenium(II) complexes reveals that the redox chemistry of the ruthenium center and the TPA unit can be independently modulated by placing EWGs or EDGs on the anionic ring of the pbpy ligand and/or installing electron donating substituents para to the amine of the TPA group. For example, the replacement of –H with –OMe para to the amine of the TPA group lowers the TPAŸ+/ TPA0 redox couple from +1.20 to +0.99 V. The Ru(III)/Ru(II) redox potential can be modulated over a range of +1.10 to +1.27 V by substitution of the anionic ring of the pbpy chelate with –OMe and –CF3 groups 12	  respectively.56 Consequently, the HOMO character can be positioned on either the metal chelate or the TPA unit.  In contrast to the electrochemical effects of substitution on the anionic ring, the relative positions of the two redox units are found to have negligible effects on the optical properties. Substitution at both R1 and R2/R3 (Figure 1.5) produces minor changes in both the intensities and shapes of the absorbance profiles.56 This finding is in stark contrast to the large spectral changes when the position of the organometallic bond is changed.57 The ability to control the redox properties without affecting the optical properties provides a platform for inducing an electronic cascade effect.68 More specifically, by careful structural control of the electron-donating moiety it is possible to increase the spatial separation between the photoinjected electrons in the TiO2 and the hole that may result in a retardation of the charge recombination.   1.4. Intramolecular Hole Transfer  Solar energy materials convert light into useful energy by efficiently separating charge: the electronically excited sensitizer injects an electron into the semiconductor to form a charge-separated pair with the hole localized on the sensitizer (Figure 1.6). Recombination of the injected electron and hole, to give ground state products represents a deleterious pathway which may reduce the efficiency of a regenerative solar cell.69 A number of strategies are currently being developed to optimize these dynamics, including the insertion of inorganic barrier layers between TiO2 and the sensitizer dye70 and the use of alternative redox couples.71 On the other hand, molecules that contain multiple components are attracting strong interest due to their potential in decreasing the recombination dynamics on TiO2.63,68,72-75  13	    Figure 1.6. Excited-state electron injection and intramolecular hole transfer for a sensitizer-linker-donor compound anchored on a TiO2 surface.   Approaches have been recently adopted using sensitizer dyes in which the dye chromophore is modified by the covalent attachment of secondary electron donors.63,64,69,76-80 By introducing such secondary electron transfer cascades within the dye structure it is possible to retard the charge recombination dynamics by increasing the physical separation between the dye-cation moiety and the surface of TiO2. Our group was the first to report that intramolecular hole transfer yields can be tuned from zero to unity through synthetic design modifications and predicted at the molecular level based on measured reduction potentials.81 In Figure 1.6, where R1 = –OMe, R2 = –CF3, R3 = –H, the TPA was oxidized prior to the ruthenium metal center and based on spectroelectrochemical data results indicated quantitative hole transfer to yield TPAŸ+-Ru(II)/TiO2(e-). For R1, R2, R3 = –H, the ruthenium metal center was oxidized prior to the TPA group and no hole transfer was observed to yield TPA-Ru(III)/TiO2(e-). In the compound where R1 = –OMe, R2 = –H, R3 = –OMe, intermediate behavior was observed, 14	  where oxidation of TPA and ruthenium occurred concomitantly and showed partial hole transfer. For this class of dyads, intramolecular hole transfer in itself had no measureable influence on the charge recombination kinetics as might have been expected based on previous studies.63,64,69,76  1.5. Project Objectives and Outline  Previous groups have shown that with some dyads, intramolecular hole transfer has been directly correlated with decreased rate constants for interfacial charge recombination. Research conducted in the Berlinguette group indicates that charge recombination was the same regardless of the spatial separation of the hole from the TiO2.81 With this in mind, this project sought to explain this dissimilar behavior.   It has long been argued that electronic communication between donor and acceptor units should depend on the geometry of the connector. Proving this concept has proved to be extremely difficult although notable attempts have been made.82,83 Harriman et al. were the first to provide a detailed examination of the influence of the bridge conformation on the donor-acceptor electronic coupling in donor-bridge-acceptor (D-B-A) systems.84 They probed the effect of torsional angles within the bridge structure on the rate of intramolecular energy transfer in a series of ruthenium(II)/osmium(II) tpy2 donor-acceptor complexes linked by ethynylene-substituted biphenyl bridges (Figure 1.7).    15	    Figure 1.7. Structural formulae for the set of ruthenium(II)/osmium(II) bis(2,2’:6’,2”-terpyridine) binuclear complexes.   It was found that, the dihedral angle could be controlled and tuned between the phenyl units by attaching a tethering strap between the two phenyl units and varying the number or carbon atoms in the strap, giving access to a wide range of dihedral angles while keeping a fixed donor-acceptor distance.84 Their results showed pronounced conformational dependence of the transfer rates, where the electronic coupling was the largest when the phenyl units were close to coplanar (φ = 30°). At the largest dihedral angle (φ = 90°), the electronic coupling decreased drastically, resulting in a measured transfer rate that decreased by a factor of 80.   In response to these observations, a strategy to regulate electron flow by reducing the electronic communication between the donor and acceptor in a family of bichromic dyes was analyzed for this thesis (Figure 1.8). These ruthenium polypyridyl compounds contain a common terpyridyl ligand with three carboxylic acid/ carboxylate groups for surface binding, and a tridentate cyclometalating ligand with a conjugated triarylamine donor group.   16	  NNRuNNNCO2HHO2CCO2-SNOMeMeOR1R2  Figure 1.8. Optimization of ruthenium-based dyads for the DSSC. Methyl groups about the bridging unit disrupts conjugation to decrease electronic communication between the TPA and metal-center to decrease the rate of interfacial recombination. Modification of  –R1 and –R2 modulates the energy of the HOMO positioning it on the metal or the TPA unit.   The bridge (thiophene spacer) between the donor and acceptor moieties is a dynamic entity in which each unit may rotate giving rise to different conformations. The addition of steric bulk about the bridge (i.e. Figure 1.8, addition of methyl groups outlined in pink) should influence the dihedral angles between the individual units within the bridge and the donor, which may strongly modulate the overall donor-acceptor electronic coupling. Under the auspices of these motivating factors, we sought to further develop the molecular platform in Figure 1.8 to examine how the optical and electrochemical properties, as well as the recombination kinetics, are affected by steric hindrance about the linker and terminal substituents at the metal chelate (R1 and R2) designated in Table 1.1.    17	  Table 1.1. Designation of Compoundsa 	   Complex  Ligand  Donor Ligand  Acceptor Ligand -R1 -R2 Ligand -R3 1 L1 -H -H L5 -CO2Me 2 L1 -H -H  -CO2H 3 L2 -CF3 -H L5 -CO2Me 4 L2 -CF3 -H  -CO2H 5 L3 -CF3 -CF3 L5 -CO2Meb 6 L3 -CF3 -CF3  -CO2Hb 7 L4 -H -OMe L5 -CO2Me 8 L4 -H -OMe  -CO2H a Counterion = NO3- for 1-8.  b Complexes were not successfully synthesized. 	  	  Chapter 2 lays out the development of the bichromic cyclometalated ruthenium(II) scaffold. Dyad molecules are of interest as they provide the opportunity to induce an electronic cascade effect that shuttles hole away from the surface. Dyes with the general formula [Ru(II)(TPA-2,5-thiophene-pbpy)(H3tctpy)] (pbpy = 6-phenyl-2,2’-bipyridine; H3tctpy = 4,4’,4”-tricarboxy-2,2’:6’2”-terpyridine) their synthesis and structural characterization will be examined. An exploration of the electrochemical and spectroscopic properties of the free ligands and the corresponding metal complexes of the dyes laid out in Chapter 2 as well. Chapter 3 presents a thorough investigation of the energetics and kinetics of the dyes synthesized in Chapter 2 through spectroelectrochemistry and transient absorption spectroscopy. The impact of steric hindrance on the interfacial charge recombination kinetics is explored. Overall conclusions and future work are found in Chapter 4 while Chapter 5 contains experimental procedures and methods.  	  	  	  18CHAPTER TWO: SYNTHESIS AND STRUCTURAL CHARACTERIZATION  2.1. Introduction  The highest certified PCE measured for a DSSC stood at 11.4% until recently.48 The dye used to achieve this PCE was the black dye and had long stood as the only “champion” sensitizer bearing a tridentate ligand. This finding prompted many research groups to synthesize black dye analogues where the isothiocyanate groups are replaced by substituted terpyridine-type ligands. The performance of these bis-tridentate ruthenium(II) sensitizers are poor, a feature that can be attributed to weak absorption of visible light. Parent complexes [Ru(tpy)2]2+ and [Ru(bpy)2(ppy)]+ with molar extinction coefficients (ε) of ~15,000 M-1cm-1 (Figure 2.1.), are pale in comparison with highly absorbing organic dyes, which have molar extinction coefficients of >55,000 M-1cm-1.53 This prompted the Berlinguette group to append a secondary organic chromophore, namely a TPA group (Figure 2.1).55   The TPA group was chosen due to the well-known synthetic modification and excellent light absorption properties.60 The light-absorbing capabilities of both the [Ru(tpy)2]2+ and [Ru(bpy)2(ppy)]+ moieties can be dramatically increased with an appended TPA chromophore, as large ε values on the order of ~40,000 M-1cm-1 are observed.55,57 The best light-absorbing motif for these dyads contained a thiophene spacer positioned between the chelate and the TPA.57 As the thiophene spacer alleviates torsional strain between the adjacent six-membered rings and further enhances the absorption envelope by enhancing conjugation.55  	  19	  NNRuNNNNNRuNNNNCO2HCO2HNNRuNXNYSN+1n++2ε = 15,500 M-1cm-1 ε = 15,800 M-1cm-1X,Y = N; ε = 57,000 M-1cm-1X = N;  Y = C; ε = 40,000 M-1cm-1    Figure 2.1. Select bis-tridentate cycloruthenated complexes and their corresponding extinction coefficients.   The dyad scaffold (Figure 2.1. c) contains two redox active units that can be independently modulated. By placing EWGs (e.g., −CF3) or EDGs (e.g., −OMe) on the anionic ring of the pbpy ligand and/or installing electron donating substituents (e.g., −H, −Me, −OMe) para to the amine of the TPA group the first oxidation can be localized to the TPAŸ+/TPA0 or Ru(III)/Ru(II) redox couples and therefore the HOMO can be positioned on either the metal or the TPA fragment (Figure 2.2). The first oxidation is localized to the TPA when EDGs are placed para to the amine of the TPA with EWGs on the anionic ring (e.g., the TPAŸ+/TPA0 and Ru(III)/Ru(II) redox couples appear at +0.98 and +1.27 V vs. NHE, respectively, when EDG = −OMe and EWG = −CF3) and consequently the HOMO is positioned on the TPA group (Figure 2.2 b). This situation is reversed when an EDG is substituted on the anionic ring and the TPA remains unsubstituted the TPA-based and metal centered oxidation waves occur at +1.20 and +1.11 V vs. NHE, respectively leaving the HOMO metal-based (Figure 2.2 a). In contrast a) b) c) 20	  to the electrochemical behavior, the relative positions of the two redox units are found to have negligible effects on the optical properties. Substitution on the TPA or the anionic ring positions produces minor changes in both the intensities and shapes of the absorbance profiles. This ability to control the redox properties without affecting the optical properties provides a distinct advantage for inducing an electronic cascade effect, a characteristic inherently dependent on the position of the HOMO. For example, having an arrangement of TPA-based HOMO and metal-based HOMO-1 levels that favor the movement of photoinduced holes toward the TPA unit (Figure 2.2. b).          21	              NNRuNNNCO2MeMeO2CCO2MeSN+1MeO                  NNRuNNNCO2MeMeO2CCO2MeSNOMeMeO+1F3C ECBRuIII/IITPA•+/0I-/ I3-π∗π∗d+1.11+1.20RuIII/IITPA•+/0 I-/ I3-π∗π∗d+1.270.98ECB  Figure 2.2. Thermodynamic positions of the frontier molecular orbitals of a) R1/R2 = −H, R3 = −OMe and b) R1 = −OMe, R2 = −CF3, R3 = −H relative to the conduction band (ECB) of TiO2 and the I-/I3- redox couple. The relative positions of the energy levels for b) are conducive to shuttling electrons towards the TiO2 and holes towards the terminal TPA unit. The energy levels for a) should not, in principle, accommodate this same effect.    An interfacial charge-separated pair can be created with an electron in the semiconductor and a hole localized on a molecular unit away from the semiconductor surface. Achieving a long-lived charge separation of the injected electron and the hole has inhibited the rate for recombination because the photogenerated hole resides further from the TiO2 surface.63,64,76 Decreased rate constants for interfacial recombination lead to higher VOCs.77,85  a) b) 22	  	  NNRuNNNCO2HHO2CCO2-F3CSNOMeMeONNRuNNNCO2HHO2CCO2-SNMeONNRuNNNCO2HHO2CCO2-SN MeOOMeh+ h+ h+	    Figure 2.3. Hole transfer processes indicating a) no hole transfer to yield TPA-Ru(III)/TiO2(e-); b) partial hole transfer; and c) hole transfer to yield TPAŸ+-Ru(II)/TiO2(e-).     The Berlinguette group synthesized dyad molecules of a structurally similar motif that are capable of modulating the extent of hole transfer.81 In Figure 2.3 a) the ruthenium metal was oxidized prior to the TPA group leading to no hole transfer, while for c) the TPA was oxidized prior to the ruthenium metal center giving quantitative hole transfer. For b) the compound showed intermediate behavior where oxidation of the TPA and ruthenium occurred concomitantly resulting in partial hole transfer. Time-dependent absorption changes revealed that regardless of the position of the hole (on the ruthenium center or the TPA) the rate of charge recombination were within experimental error the same.81 As a means of modulating the electron transfer processes further, I have set out to modify the bridging unit.  It has been shown in the literature that the bridge conformation has a pronounced influence on the donor-acceptor electronic coupling in donor-bridge-acceptor (D-B-A) a) b) c) 23	  systems. There have been many quantum mechanical calculations of the electronic coupling in molecular bridged structures where conformational flexibility is implicated.86,87 There remains only two experiments on bridged systems that clearly show the angular dependence that has been predicted by these calculations.84,88 The authors controlled and tuned the dihedral angle in their bridged structures by attaching a tethering strap, giving access to a wide range of dihedral angles while keeping a fixed donor-acceptor distance (Chapter 1, Figure 1.7). The results show a pronounced conformational dependence on energy transfer rates, hence the electronic coupling was the largest when the donor and acceptor units were close to coplanar and at the largest dihedral angle the electronic coupling decreased drastically.88 In response to this, the addition of steric bulk about the bridge (i.e. Figure 2.4, addition of methyl groups) was adopted to influence the dihedral angles between the individual units within the bridge and the donor to modulate the overall donor-acceptor electronic coupling.  NNRuNNNCO2HHO2CCO2-SNOMeMeOR1R2ϕ  Figure 2.4. Optimization of ruthenium-based dyads for the DSSC. The addition of methyl groups about the bridging unit influences the dihedral angle between the TPA and thiophene.  24	  Building on the Berlinguette groups’ previous studies, this work has expanded the development of the dual-chromophore scaffold, [Ru(TPA-pbpy)(Me3tctpy)], by incorporating methyl groups  to demonstrate that changing the conformation of the bridge separating the TPA and ruthenium bis-tridentate chromophores produces a measurable influence on intramolecular hole transfer and charge recombination kinetics. Cognizant that the energy levels of the two redox-active chromophores can be independently manipulated, the series of sensitizers was synthesized to further exploit the substitution on the TPA chromophore and the anionic ring of the pbpy chelate with EWGs and EDGs. (Figure 2.5)  NNRuNNNCO2HHO2CCO2-SNOMeMeOR1R2  Complex Substituent −R1 −R2 2 −H −H 4 −CF3 −H 8 −H −OMe  Figure 2.5. Numbering scheme for representative bichromic cyclometalated ruthenium(II) sensitizers with EDGs/EWGs positioned at –R1/−R2.   25	  The following discussion will offer an overview of the synthesis and structural characterization of the precursors P1-P7, ligands L1-L4 and title complexes 1-8. The title complexes were successfully prepared by exploiting a modular ligand synthetic approach involving the coupling of a TPA-functionalized boronic-ester to halide-derivatized tridentate chelates following standard Suzuki methodologies. The binding of the ensuing ligands to a ruthenium precursor follows standard procedures.55-57,62,89,90 The structural identities of all ligands and complexes were confirmed by a combination of NMR spectroscopy, mass spectrometry, and/or EA. The chapter then moves to describe how the optical and electrochemical properties are affected by the steric hindrance about the bridge in the tridentate TPA-bearing ligand, and by terminal substituents at the metal chelate (e.g., EDGs and EWGs at R1 and R2).  2.2. Synthesis of Title Compounds  A modular synthetic approach (Scheme 2.1-2.3) was used to isolate the library of TPA functionalized tridentate ligands in Chapter 1, Table 1.1. The synthesis of each of these donor ligands was achieved in reasonably high yield utilizing well-established synthetic methods.  The TPA precursor P1 was synthesized by Ullmann coupling in a yield of ~80% (Scheme 2.1). The bromination of P1 at the para position was performed using n-bromosuccinimide in ethyl acetate at room temperature. The desired bromotriarylamine was recovered in a yield of ~80%.    26	  Scheme 2.1. Synthesis of Precursors P1-P2.  NOMeMeONH218-crown-6K2CO3Cu powdero-dichlorobenzene72hrs, N2OMeI EtOAc RT, overnightNOOBrNOMeMeOBrP1 P282% 81%     The preparation of the Suzuki reagent P3 was achieved through a Miyaura borylation in a yield of 32% to give the pinacol ester functionalized triarylamine (Scheme 2.2). The reaction conditions of the Miyaura procedure were optimized (outlined in Appendix C) to give the best result achieved with 2.2 equivalents of bis(pinacolato)diboron in the presence of 20 mol % of catalyst. The Grignard method and lithiation method for synthesis of borylated products were unsuccessful (Appendix C).   Scheme 2.2. Synthesis of Precursor P3. NOMeMeOBrPd(dppf)Cl2, KOAcDMSO80oC. overnight, N2OBOBOONOMeMeOBOOP2 P381% 32%   Precursors P4-P7 were synthesized through Kröhnke condensations. The Kröhnke salt precursors were synthesized in yields of 67-98% and further reacted with the previously reported (E)-3-(5-bromothiophen-2-yl)-1-(pyridine-2-yl)prop-2-en-1-one in 27	  Kröhnke condensations to yield the bromothiophene-substituted pbpy platform (Scheme 2.3) in yields of 31-73%.  Scheme 2.3. Synthesis of Precursors P4-P7.   S CHON N SOKOHMeOH/ H2OBrBrO+NNR1SBrR2ammonium acetateformamidereflux, overnightP4: R1 = -H, R2 = -H (31%)P5: R1 = -CF3, R2 = -H (73%)P6: R1 = -CF3, R2 = -CF3 (38%)P7: R1 = -H, R2 = -OMe (57%)R1Opyridine, I2refluxovernight, N2NOR1IR2 R2R1 = -H, R2 = -H (67%)R1 = -CF3, R2 = -H (98%)R1 = -CF3, R2 = -CF3 (90%)R1 = -H, R2 = -OMe (78%)   Precursors P4-P7 were further reacted with the Suzuki reagent P3 in a Suzuki coupling, to give the desired ligands, L1-L4 (Scheme 2.4), in yields of 35-71%.  Scheme 2.4. Synthesis of Ligands L1-L4.  NNSNNR1SBrK2CO3Pd(PPh3)4DMF70oC 20hNOMeMeOBOONOMeMeOR1R2R2L1: R1 = -H, R2 = -H (35%)L2: R1 = -CF3, R2 = -H (19%)L3: R1 = -CF3, R2 = -CF3 (71%)L4: R1 = -H, R2 = -OMe (26%)   28	    The construction of the cyclometalated complexes was generally more successful when the cyclometalation step followed the installation of the tpy-based fragment.57 Consequently, the cyclometalated complexes were achieved through the reaction of the Ru(L5)Cl3 synthon with the corresponding ligand in a polar solvent (i.e., MeOH/ H2O) in the presence of base; the polar solvent is needed to facilitate the dissociation of the Cl- ligand from the inner sphere. The increased hydrophobicity of the complex engendered by the TPA unit requires the addition of one equivalent of THF to the solvent; thus, a 5:1:1 MeOH/ H2O/ THF solvent combination enables the formation of the target bichromic methyl ester complexes 1,3 and 7. The methyl ester complexes were readily purified using column chromatography and isolated in yields of 40-83% (Scheme 2.5).              29	  Scheme 2.5. Assembly of Complexes 1, 3, 5, and 7. NNSNOMeMeONNRuClClNClCO2MeMeO2CCO2Men-ethylmorpholineAgNO3MeOH/ H2O/ THF (5:1:1)NNRuNNNCO2MeMeO2CCO2MeSNOMeMeOR1R1R2R2                        Substituent           YieldComplex        R1            R2           1:                  -H            -H             72%3:                  -CF3        -H             40%5:                  -CF3        -CF3 a       7:                  -H            -OMe        83%   aComplex was not successfully synthesized.   Complexes 2, 4, and 8 were prepared by hydrolyzing the ester precursors using triethylamine in aqueous DMF (Scheme 2.6).                  30	  Scheme 2.6. Assembly of Complexes 2, 4, 6, and 8.  NNRuNNNCO2MeMeO2CCO2MeSNOMeMeOR1R2                       Substituent          YieldComplex        R1            R2           2:                  -H            -H             90%4:                  -CF3        -H             88%6:                  -CF3        -CF3 a8:                  -H            -OMe        78%NNRuNNNCO2HHO2CCO2HSNOMeMeODMF/ H2O/ NEt3(3:1:1 v/v)reflux, overnightR1R2 a Complexes were not successfully synthesized    The structural identities of all ligands and complexes were confirmed by a combination of multinuclear NMR spectroscopy, mass spectrometry, and/or elemental analysis. The identity of each of the complexes can be unambiguously verified by 1H/13C NMR (1D and 2D) techniques owing to the sufficient separation of the aromatic signals and asymmetry of the complexes (Chapter 5). A collection of representative 1H NMR spectra for the acid complexes (e.g., 2,4, and 8) are provided in Figure 2.6 to illustrate the effect of the substitution on the anionic ring of the pbpy chelate with EWGs or EDGs.  31	  NNRuNNNCO2HHO2CCO2HSNOMeMeOF3C npqNNRuNNNCO2HHO2CCO2HSNOMeMeOnpqoNNRuNNNCO2HHO2CCO2HSNOMeMeOnpoMeO1+1+ 1+8 2 4     Figure 2.6. 1H NMR spectra for CDCl3 solutions of 2, 4 and 8 at 298 K highlighting how substituents affect the electron density on the anionic ring. Color scheme: green, Hq; orange, Ho; blue, Hp; red, Hn.    8 2 4 32	  A signature of cyclometalation of the TPA-substituted pbpy ligand is the upfield shift of the signal corresponding to the proton ortho to the Ru-C bond (i.e., –Hq) that arises because of the proximity of the anionic carbon. This signal is observed for compounds with either –H (e.g., 2) or –CF3 (e.g., 4) on the anionic ring (Figure 2.6). The electron withdrawing nature of the –CF3 group is revealed in the downfield chemical shift of the proton ortho to the Ru-C bond, Hq, of 4 (Hq = 5.88 ppm) relative to the –H substituted analogue 2 (Hq = 5.58 ppm). The most upfield signal in the aromatic region for –OMe-substituted complex 8 is not Hq but is instead a doublet corresponding to the resonance signal of the proton meta to the Ru-C bond, Hp, at 6.07 ppm. This signature provides direct evidence that the –OMe group appears at the R2 position (i.e., ortho to the Ru-C bond) rather than at the R1 position.  Because the position of the substituent on the phenyl ring of the pbpy chelate is found to fluctuate in the series (i.e., at either R2 or R3), Hn and Hp emerge as better spectroscopic handles to probe the electronic effects of substitution for this particular series. In this regard, the chemical shift of Hp follows the expected trend of electron density on the anionic ring, e.g., 8 (6.07 ppm), 2 (6.50 ppm), and 4 (6.74 ppm). The same can be said for Hn although the signal for Hn in all complexes is overlapping with other signals; in all cases the chemical shift of Hn follows the expected trend of electron density on the anionic ring, e.g., 8 (7.73-7.69 ppm), 2 (7.97-7.90 ppm), and 4 (8.21-8.19 ppm).    It has been previously established that C-H activation occurs through a concerted electrophilic metalation/deprotonation reaction.59 The high-valent Ru(III) precursor and electron-withdrawing methyl-ester groups afford an electrophilic metal center primed for electrophilic metalation. C-H activation takes place para to the substituent on the anionic 33	  ring for the complex bearing a –CF3 substituent on the anionic ring (e.g., 4). Taking into account the electron-withdrawing character of the –CF3 group, it is not remarkable that the C-H bond para to the substituent is activated to form the Ru-C bond. It was anticipated that the –OMe substituent would also appear para to the Ru-C bond due to steric considerations; however, the C-H activation step is found to occur ortho to the –OMe group because electrophilic metalations involving substituted aromatic molecules typically show little selectivity between different C-H bonds, and the observed selectivity is usually a consequence of steric factors. This trend is not observed in the case of 8. An extrapolation of the electrochemical data for related complexes indicates the –OMe groups para and ortho to the organometallic bond lower the metal-based oxidation potential by ~130 and ~70 mV, respectively.59 Consequently, the ortho isomer is thermodynamically stable and therefore the favored product as witnessed in previous literature.56,59  2.3. Electrochemical Data   The electrochemical properties of the free ligands and the corresponding metal complexes were examined by cyclic voltammetry. Electrochemical potentials were measured in CH2Cl2 with a 0.1 M NBu4BF4 supporting electrolyte at a scan rate of 100 mV/s. Measurements were referenced to ferrocene ([Fc]/[Fc]+) internal standard followed by conversion to NHE ([Fc]/[Fc]+) vs. NHE = +765 mV in CH2Cl2).56 Relevant redox values are collected in Table 2.1. The redox properties of similar TPA-substituted ligands have been discussed previously and the careful assignment of the oxidative behavior was aided by reference to these compounds.55-57 Note that the electrochemistry, UV-vis and emission data were recorded in DCM, MeOH, and MeCN, respectively. This 34	  inconsistency is due to the desire to directly compare results from these experiments to previously reported compounds. In previous experiments the inconsistency was due to a consequence of the solvent medium affecting the data resolution in certain cases.57 Differential pulse voltammetry (DPV) was employed to help resolve closely positioned oxidation waves. For the ligands (L1-L4), there is a single reversible one-electron oxidation (E1/2ox = +1.00-1.03 V) localized to the TPA portion of the ligand (i.e., TPAŸ+/TPA0). The oxidation potential of the free ligands remains static regardless of substitution on the anionic ring. Work by Bender, et al., shows that substitution on the triarylamine backbone can affect the oxidation potential; by placing EDGs around the backbone the oxidation potential of the redox couple is reduced and the presence of EWGs does the opposite.91 In the complexes reported (2,4, and 8) the substitution of the TPA unit remains the same. The substitution on ligands L1-L4 is located on the phenyl ring of the pbpy and is spatially separated from the triarylamine, thereby leading to the conclusion that the electron density on the pbpy ligand has little to no effect on the TPA unit. This finding is expected as the conjugation through the pbpy and the TPA units is diminished. Also, it is reflected in similar complexes reported by Robson et al., where the electron density at the phenyl ring has little to no effect on the TPA unit even when conjugation through the pbpy and the TPA units is not disrupted.56 After coordination to the ruthenium metal, the position of this oxidation wave remains static (Figure 2.7) [e.g., ~1.0 V for L1 and 1.0 V for the corresponding metal complex 2]. This indicates that the electron density at the metal site has little effect on the TPA unit.    35	  Table 2.1. Summary of Spectroscopic and Electrochemical Properties of Ligands L1-L4 and Complexes 2, 4, and 8.    Compound UV-vis absorbance dataa: λmax nm (ε × 103, M-1.cm-1) Emission datab λem, nm (λex) E1/2, V ns NHEc  Ru(III)/ Ru(II)  TPAŸ+/ TPA0 L1 310 (43.3), 291 (44.3) 389 (252) 607 (340) d 1.03 2 671sh (2.5), 575sh, 522 (15.2), 424 (18.6), 328 (44.7) d 1.20 (75) 1.00 (66) L2 311 (39.7), 291 (39.4) 424 (247) 621 (395) d 1.00 4 648sh (3.0), 552sh, 516 (17.1), 417 (16.4), 324 (50.7) d 1.28 (85) 0.99 (72) L3 312 (40.2), 288 (40.7) 422 (250) 642 (396) d 1.01 L4 307 (42.1), 295sh (41.1) 378 (249) 606 (347) d 1.01 8 670sh (2.7), 563sh, 529 (15.5), 426 (19.0), 326 (48.2) d 1.14 (85) 1.01 (67) aData collected in MeOH. bData collected in MeCN; λex values indicated in parentheses with units of nm. cData collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at 100 mV/s and referenced to a [Fc]/[Fc]+ internal standard followed by conversion to NHE; [Fc]/[Fc+] = +765 mV vs. NHE in CH2Cl2; values in parentheses are the  ΔE values of Ep,a and Ep,c given in mV determined from cyclic voltammetry experiments . dNot observed. Superscript “sh” indicates shoulder.   An anodic sweep of each of the solutions containing the cyclometalated complexes typically produces two consecutive reversible single-electron oxidation processes that correspond to the oxidation of the TPA unit and ruthenium(II) metal; the differences in Ep,a and Ep,c (i.e., ΔE) are provided in Table 2.1. No reduction was observed for complexes 2, 4 and 8 within the electrochemical window of CH2Cl2.   While the oxidation potential of the TPAŸ+/TPA0 remains static before and after coordination to ruthenium. The oxidation potential of the Ru(III)/Ru(II) redox couple is 36	  affected by substitution of the anionic ring, where the oxidation potential increases with decreasing electron density on the pbpy chelate. With installation of the –CF3 group at the R1 position, the Ru(III)/Ru(II) redox couple resides at 1.28 V, which is +80 and +140 mV greater than the cases where R1 = –H and R2 = –OMe, respectively. This is not surprising as in general, cyclometalated ruthenium complexes contain a highest occupied molecular orbital (HOMO) that is extended over the metal and anionic portion of the cyclometalating ligand.44,90,92-96 Thus the electron density at the anionic ring will affect the oxidation potential of the Ru(III)/Ru(II) redox couple. The incorporation of electron-withdrawing groups on the anionic ring stabilizes the HOMO level by strengthening the Ru-C bond.97 Therefore the oxidation potential of the Ru(III)/Ru(II) redox couple will be higher for 4 relative to 2 and 8. Similarly, the incorporation of electron-donating groups on the anionic ring destabilizes the HOMO level by weakening the Ru-C bond causing the oxidation potential of the Ru(III)/Ru(II) redox couple to be lower for 8 than for 2 and 4. Thus, giving an overall trend of the oxidation potential of the Ru(III)/Ru(II) redox couple increasing with decreasing amount of electron density on the anionic ring.  37	    Figure 2.7. Cyclic voltammograms for ligand L1 and the corresponding carboxylic acid metal complex 2 in CH2Cl2 at ambient temperatures (scan rate = 100 mV/s). Dashed lines emphasize that Ep,a and Ep,c of the TPAŸ+ /TPA0 couple are the same as those for the free ligand and complex.    2.4. Optical Properties.   Electronic absorption and emission data were collected to delineate the effects of substitution on the anionic ring (Table 2.1). UV-vis absorption measurements were performed in MeOH solutions for the free ligands L1-L4 and complexes 2,4 and 8. Representative UV-vis spectra are provided in Figure 2.8 and the λmax values are listed in Table 2.1.  Each of the free TPA-substituted ligands displays two relatively broad intense absorption bands centered within the 288-312 nm range that arise from a series of 38	  intramolecular π-π* transitions emanating from the TPA fragment to the π* system of the pbpy fragment. These same transitions are classified herein as intraligand charge transfer (ILCT) transitions when the ligand is bound to the ruthenium metal center. Ligation to the metal center renders a broad and intense absorption envelope for each of the complexes due to multiple ILCT and MLCT transitions.   The general assignment of the principal electronic transitions for the title complexes is made possible by the extensive library of related compounds in previous work.56,57 The optical spectra for 2, 4 and 8 in Figure 2.8 reveal a slight effect on the intensities and positions of the absorption spectra when different substituents are installed at the R1/R2 positions on the pbpy chelate. The position of the lowest-energy maxima reflects a higher metal-based HOMO level with progressively greater electron density on the anionic ring; e.g., λmax follows the trend 8 (529 nm) > 2 (522 nm) > 4 (516 nm).  The optical spectra of complexes 2 and 8 (Figure 2.8) are very similar while complex 4 appears slightly blue shifted in comparison. This arises as in general, cyclometalated ruthenium complexes contain a HOMO that is extended over the metal and anionic portion of the cyclometalated ligand, thereby enabling substituents positioned on the anionic ligand to directly affect the position of the HOMO energy level. These optical properties are aligned with electrochemical trends; the installation of EWGs on the phenyl ring of the pbpy stabilizes the HOMO level (i.e., the Ru(III)/Ru(II) redox couple) and makes it more difficult to oxidize leading to a higher oxidation potential. For example, the HOMO energy of the parent pbpy system (ca. +1.20 V vs. NHE, Table 2.1) is lowered by 80 mV with the addition of a –CF3 group. This is reflected in the optical 39	  spectrum, as the band gap for 4 is larger due to this stabilization, giving rise to a spectral blue shift.     Figure 2.8. UV-vis absorption spectra demonstrating the optical response to the substituents at the pbpy chelate (e.g., 2, R1/R2= −H; 4, R1 = −CF3, R2 = −H; 8, R1 = −H, R2 = −OMe).    The complexes 2, 4, and 8 have decreased light absorption throughout the visible spectrum in comparison to their conjugated counterparts (Figure 2.9). The conjugated complexes had molar extinction coefficients of up to 44.9 × 103 in the visible region,56 while the unconjugated complexes have molar extinction coefficients of up to 19.0 × 103 in the visible region. The complexes 2, 4, and 8 and ligands L1-L4 contain additional methyl groups on the phenyl ring ortho to the thiophene, this results in some torsional strain between both the TPA unit and thiophene linker that suppresses conjugation, thus resulting in decreased light absorption throughout the visible spectrum.  40	   Figure 2.9. UV-vis spectra collected in MeOH at ambient temperature of 4 (red trace) and the conjugated counterpart (black trace).    The luminescence properties of the complexes (2, 4, 8) and ligands (L1-L4) were collected in dry, degassed acetonitrile at room temperature. Relevant emission data (λem) is collected in Table 2.1. The complexes 2, 4, and 8 were non emissive. Ligands L1-L4 are all moderately emissive when excited at wavelengths corresponding to their λmax. Emission maxima generally follow a trend corresponding to λmax values with electron poor ligands emitting furthest in the red region.  2.5. Computational Results  B3LYP/LanL2DZ DFT calculations were carried out on all compounds to aid in the determination of the electronic structure (Figure 2.10). All reported values have been converted to a thermodynamic scale of V vs. NHE (with the assumption that 0V vs. NHE corresponds to a vacuum level of -4.5 eV).98     41	     Figure 2.10. Summary of DFT results for 2, 4, and 8. H atoms omitted for clarity.   The electronic structure of 2, 4, and 8 are very similar. The LUMO and LUMO+1 levels are localized on the tpy ligand, with the cyclometalating ligand contributing to the LUMO+2 level. The electron density of the HOMO for all cyclometalated complexes is found primarily on the TPA unit. The π* orbitals of the ligands are shifted to higher energy and are poised for electron injection into ECB of TiO2 while the ground-state oxidation potentials are properly positioned to interact with the electrolyte. After the geometry of the complexes were optimized at DFT-B3LYP level with a 6-31G* basis set the lowest energy conformation was determined to be at a dihedral angle of 109.5° 8 4 2 42	  between atoms S58, C61, C63, and C65 for complex 2. This finding demonstrates a planar conformation is not favored.   NNRuNNNCO2HHO2CCO2HSNOMeMeO+158616365 Figure 2.11. Atom labels for complex 2. Blue area highlighted for calculated dihedral angle.    To explore the energies of potential conformers about the bridge a potential energy scan (PES) study of the unsubstituted dye (2) is performed. A PES scan determines the internal energy barrier to rotation about the bridge by rotating the bond between the thiophene and the triarylamine. At first the geometry of 2 was optimized at DFT-B3LYP level with a 6-31G* basis set. The lowest energy conformation was determined to be at a dihedral angle of 109.5° between atoms S58, C61, C63 and C65 (Figure 2.11). A potential energy surface scan was performed at the same level of theory starting with the optimized geometry and varying the dihedral angle between the thiophene and triarylamine planes between 0° and 360° in increments of 10°. The potential energy scan obtained is plotted in Figure 2.12. Local minima are identified in the PES at an ideal dihedral angle of 109.5°. The lowest energy minima arise due to the 43	  lowest amount of steric repulsion of triarylamine and thiophene groups. Local maxima are identified at 0° and 180°. The highest energy maxima arise due to the highest amount of steric repulsion of triarylamine and thiophene groups in a planar conformation.    Figure 2.12. Potential energy for rotation about the dihedral angle of atoms S58, C61, C63 and C65 in complex 2.   2.6. Summary. The successful synthesis of each of the complexes 2, 4, and 8 was achieved in reasonably high yield utilizing well-established synthetic methods. Precursors P4-P7 were synthesized through Krönke condensations to yield the bromothiophene-substituted pbpy platform, which were further reacted with Suzuki reagent P3 to give the desired ligands, L1-L4 in high yields. The synthesis of the cyclometalated complexes were achieved through reaction of the Ru(L5)Cl3 synthon with the corresponding ligand, producing the methyl ester complexes 1, 3 and 7 in high yield after chromatographic 44	  purification, and finally the ester groups were hydrolyzed to give the corresponding acid complexes in high yield. The structural identities of all the ligands and complexes were confirmed by a combination of NMR spectroscopy, mass spectrometry and/or EA. 1H NMR (1D and 2D) spectroscopy proved to be a particularly effective diagnostic tool for these complexes because of separation of the aromatic signals and the inherent asymmetry of the complexes (Chapter 5). Building on previous studies, the development of the dual-chromophore scaffold, [Ru(TPA-pbpy)(Me3tctpy)], shows that still, with steric hindrance about the bridge in the tridentate TPA-bearing ligand, we can systematically tune the electrochemical behavior of the ruthenium units. The electronic properties of the electrophore can be manipulated to make the Ru(III)/Ru(II) couple more or less oxidizing than the TPA unit. This feature is possible because the ground-state oxidation potentials of the Ru unit can be modulated over a wide range of potentials: ΔE1/2 = 140 mV for the Ru(III)/Ru(II) couple.  In contrast to the electrochemical behavior, the relative positions of the redox units are found to have negligible effects on the optical properties: substitution at both the R1 and R2 positions produces minor changes in both the intensities and shapes of the absorbance profiles. As expected though, by adding steric hindrance about the bridge, and the overall reduction in conjugation, the molar extinction coefficients were significantly decreased compared to their conjugated counterparts. The PES scan confirmed that the highest energy conformer is attributed to a planar conformation.  	  	  	  	  	  	  45CHAPTER THREE: INTERFACIAL ENERGETICS AND KINETICS  3.1. Introduction  Light-to-electricity energy conversion in DSSCs is initiated by excited-state electron transfer from a dye molecule to a semiconductor surface.10,12 The oxidized dye formed after electron injection is regenerated by intermolecular hole transfer to a donor in solution.12 Electrons in the TiO2 can also recombine with the oxidized dye, a process that limits efficiency in DSSCs. Studies of dyad molecules capable of intermolecular hole transfer have revealed decreased rate constants for interfacial charge recombination (Figure 3.1).63,69,76,79,80  Figure 3.1. Listing of representative dyad molecules capable of intramolecular hole transfer: a) [Ru(dcbH2)2(4-CH3,4’-CH2-PTZ,-2,2’-bipyridine))]2+ (PTZ = phenothiazine); b) [Ru(TPA-tpy)(tpyPO3H2)].   Hole transfer to a covalently linked donor has resulted in decreased recombination rates of three orders of magnitude for a) and one order of magnitude for b) as compared to corresponding model compounds lacking a secondary redox-active site (Figure 3.1). 63,77 In contrast, work done previously in the Berlinguette group demonstrated that the NNRuNNNNPO3H2NMeO OMeNNNN NNRuNSHO2CHO2C CO2HCO2Ha) b)46	  rate of interfacial recombination between electrons in TiO2 and the oxidized sensitizer were the same regardless of the spatial location of the hole.81 The similar rates of interfacial recombination in these compounds can be rationalized by the highly conjugated nature of the thiophene spacer.81 To disrupt this conjugation and to probe the rate of interfacial electron transfer the complexes in Figure 3.2 are proposed. Methyl groups are installed ortho to the thiophene unit to create steric bulk, which should have the overall effect of decreasing conjugation within the molecule by discouraging a planar conformation. The dyads all maintain a common structural motif with redox potentials that can be systematically tuned as demonstrated in Chapter 2.   NNRuNNNCO2HHO2CCO2HSNOMeMeO+1MeONNRuNNNCO2HHO2CCO2HSNOMeMeO+1NNRuNNNCO2HHO2CCO2HSNOMeMeO+1F3C8 2 4  Figure 3.2. Designation of compounds. Counterion = NO3- for 8, 2, and 4.   These dyad molecules (Figure 3.2) are capable of demonstrating an interfacial charge-separated state comprising of an injected electron and an oxidized donor (Figure 3.3). A sensitizing dye molecule absorbs a photon to create an excited state that initiates 47	  two charge transfer reactions: (1) electron transfer to a TiO2 nanocrystallite, and (2) intramolecular hole transfer to a covalently linked donor.  Linker DonorSTiO2h+e-hv  Figure 3.3. Excited-state electron injection and intramolecular hole transfer for a sensitizer-linker-donor compound anchored on a TiO2 surface.   The charge-separated state is proposed to exist in a redox equilibrium (Scheme 3.1) where the hole will either exist on the metal center (TiO2(e-)|Ru(III)−L−TPA) or the TPA unit (TiO2(e-)|Ru(II)−L−TPAŸ+) after electron transfer to the nanocrystallite.99 The donor-linker-acceptor compounds (2, 4, and 8; Figure 3.1) with their broad range of Ru(III)/Ru(II) redox potentials have been characterized so that the redox equilibrium in Scheme 3.1 can be systematically probed.  Scheme 3.1. The Interfacial Redox Equilibrium Under Study.  TiO2| Ru(II)–L−TPA hv TiO2(e-)| Ru(III)−L−TPA Keq TiO2(e-)| Ru(II)−L−TPAŸ+   The dyads were anchored to mesoporous nanocrystalline TiO2 thin films by reactions in MeOH solutions as was previously described and are abbreviated as 2/TiO2, 4/TiO2, 8/TiO2.57 Herein, in situ spectroelectrochemistry is used to quantify the interfacial energetics (redox chemistry) of 2/TiO2, 4/TiO2, and 8/TiO2 in a 0.5 M LiClO4/CH3CN solution to predict the extent of hole transfer that will occur. The nanosecond transient 48	  absorption spectroscopy was used to quantify the interfacial charge recombination between TiO2(e-) and the oxidized compound.  This work is done in collaboration with Prof. Gerald Meyer and the Meyer group at the University of North Carolina at Chapel Hill. I synthesized the title complexes 2, 4, and 8 and Dr. Ke Hu performed the transient absorption (TA) and spectroelectrochemical experiments.  3.2. Spectroelectrochemistry.  The carboxylic acid forms of the complexes were anchored to mesoporous anatase TiO2 thin films in very diluted loading solutions (~10-6 M) overnight to achieve high surface coverage.  The molecules on TiO2 were assumed to be isolated and did not communicate with each other.  Cyclic voltammetry of the sensitized TiO2 or nanoITO films showed significant overlap of the two redox waves at a scan rate as slow as 5mV/s. Spectroelectrochemistry was carried out to estimate the reduction potentials and assign the redox processes. Figure 3.4 shows representative UV-vis spectral changes upon oxidation for the complexes on TiO2 at increased positive applied potential (50 mV steps).     49	  400 500 600 700 800 900 10000.00.51.01.52.02.5AbsorbanceWavelength (nm) 188 685 728 767 788 811 832 850 869 885 901 916 929 943 956 969 987 1002 1023 1044 1067 1091 1119 1148mV vs. NHEADB203/TiO2 in 0.5 M LiClO4 CH3CN	  	  400 500 600 700 800 900 1000-1.0-0.50.00.51.01.52.0ADB203/TiO2 in 0.5 M LiClO4 CH3CNΔ AbsorbanceWavelength (nm) 685 728 767 788 811 832 850 869 885 901 916 929 943 956 969 987 1002 1023 1044 1067 1091 1119 1148mV vs. NHE	  	  400 500 600 700 800 900 10000.00.51.01.52.0ADB166/TiO2 in 0.5 M LiClO4 CH3CNAbsorbanceWavelength (nm) 180 694 782 825 857 881 900 920 935 951 965 978 994 1011 1032 1052 1076 1099 1124mV vs. NHE	  	  400 500 600 700 800 900 1000-1.0-0.50.00.51.01.5ADB166/TiO2 in 0.5 M LiClO4 CH3CNΔ AbsorbanceWavelength (nm) 694 782 825 857 881 900 920 935 951 965 978 994 1011 1032 1052 1076 1099 1124mV vs. NHE	  	  400 500 600 700 800 900 10000.00.51.01.52.0ADB167/TiO2 in 0.5 M LiClO4 CH3CNAbsorbanceWavelength (nm) 187 684 734 784 811 835 857 880 899 905 915 931 946 961 979 993 1007 1020 1033 1048 1064 1080 1100 1126 1158mV vs. NHE	  	  400 500 600 700 800 900 1000-1.0-0.50.00.51.01.5ADB167/TiO2 in 0.5 M LiClO4 CH3CNΔ AbsorbanceWavelength (nm) 684 734 784 811 835 857 880 899 905 915 931 946 961 979 993 1007 1020 1033 1048 1064 1080 1100 1126 1158mV vs. NHE	  	  Figure 3.4. UV-vis-NIR absorption spectra of (a) 2/TiO2 and (c) 4/TiO2 and (e) 8/TiO2 measured at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions. UV-vis-NIR absorption difference spectra of (b) 2/TiO2 and (d) 4/TiO2 and (f) 8/TiO2.  	  	  	  a) b) d) c) e) f) 50	  Initial oxidation of 2/TiO2, 4/TiO2, and  8/TiO2 to 2+/TiO2, 4+/TiO2, and 8+/TiO2, respectively, showed an absorption decrease at 440 nm and 510 nm (Figure 3.4).  They show bleaches of the metal to ligand charge transfer (MLCT) bands, indicating that oxidation occurred at the ruthenium metal center. A marked absorption band at 750 nm in all cases is characteristic of NArŸ+ absorption indicating that oxidation occurred at the triarylamine.81,99 The absorption band at 750 nm serves as a probe for hole transfer in transient absorption studies. For both 2/TiO2 and 8/TiO2 the immediate decrease in absorption at 440 and 510 nm indicated that the first oxidation was ruthenium-centered and was followed by the NAr3-centered oxidation at more positive potentials. In the case of 4/TiO2, the order of the redox chemistry was reversed. The immediate appearance of a strong absorption band at 750 nm indicated that the first oxidation was NAr3 centered. Followed by the ruthenium-centered oxidation at more positive potentials. Figure 3.4 (spectra b,d,f) absorption difference spectra reveals a lack of clear isosbestic point (wavelength, where at least two chemical species have the same molar extinction coefficient). Unclear isosbestic points gives evidence that the reaction is preceding with the formation of an intermediate. In order to determine the reduction potentials, the formation of this intermediate has to be accounted for.  To obtain the intermediate UV-vis spectrum (Ru(III)-NAr3 or Ru(II)-NAr3Ÿ+) you have to assume that the initial and final oxidations are clean. Assuming that the first oxidation is a clean one-electron process can be confirmed by maintaining a set of isosbestic points. When the first oxidation is turned on, as seen in Figure 3.5, you can see a single wavelength where there is no change in absorbance (circled in red for clarity).   51	  400 500 600 700 800 900 1000-0.25-0.20-0.15-0.10-0.050.000.05Δ AbsorbanceWavelength (nm) 685 728 767 788 811 832 850 869 885 901 916 929 943 956 969 987 1002 1023 1044 1067 1091 1119 1148mV vs. NHE  Figure 3.5. Initial oxidation absorbance difference spectrum 8/TiO2 measured at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions. Circled in red is the set of isosbestic points.    When the second oxidation is turned on, the first set of isosbestic points will shift to a different wavelength and when the oxidation reaches towards the end as the final oxidation is clean. Shown in Figure 3.6 below (circled in grey for clarity).   	  52	  400 500 600 700 800 900 1000-1.0-0.50.00.51.01.52.0ADB203/TiO2 in 0.5 M LiClO4 CH3CNΔ AbsorbanceWavelength (nm) 685 728 767 788 811 832 850 869 885 901 916 929 943 956 969 987 1002 1023 1044 1067 1091 1119 1148mV vs. NHE  Figure 3.6. UV-vis-NIR absorption difference spectra of 8/TiO2 at indicated applied potentials in 0.5 M LiClO4 CH3CN solutions.   The reasoning stands that if the two-redox reactions are well separated the intermediate spectrum should go through the second set of isosbestic points. The initial change in absorption spectrum is normalized to the second set of isosbestic points. Then, the normalized delta absorption spectrum is added to the fully reduced ground state spectrum to obtain the intermediate spectrum, shown in Figure 3.7 (red trace in a, b, and c).      	  53	  400 500 600 700 800 900 10000.00.51.01.52.02.5ADB203/TiO2 in 0.5 M LiClO4 CH3CNAbsorbanceWavelength (nm) RuII-NAr3 RuIII-NAr3 RuIII-NAr3+ 400 500 600 700 800 900 10000.00.51.01.52.0DOS of ADB166/TiO2 in 0.5 M LiClO4 CH3CNAbsorbanceWavelength (nm) RuII-NAr3 RuIII-NAr3 RuIII-NAr3+	  400 500 600 700 800 900 10000.00.51.01.52.0ADB167/TiO2 in 0.5 M LiClO4 CH3CNAbsorbanceWavelength (nm) RuII-NAr3 RuII-NAr3+ RuIII-NAr3+  Figure 3.7. The UV-vis absorption of (a) 8/TiO2, (b) 2/TiO2, or (c) 4/TiO2 in 0.5 M LiClO4/CH3CN in the 2/TiO2, 4/TiO2, or 8/TiO2 (black); 2+/TiO2, 4+/TiO2, or 8+/TiO2 (red), and 22+/TiO2, 42+/TiO2, or 82+/TiO2 (blue) states. Note that the Ru(II)-NAr3 and Ru(III)-NAr3+ states are mathematically calculated.    The UV-vis absorption spectra (Figure 3.7) illustrate the ground, singly, and doubly oxidized states of complexes 2, 4, and 8 on TiO2 (Figure 3.7). Spectral modeling of the absorption spectra of the ground state, Ru(II)-NAr3, and doubly oxidized state, Ru(III)-NAr3+ were mathematically calculated fits derived from the spectroelectrochemical data (Figure 3.4). The UV-vis absorption spectra of the singly oxidized state were assigned as Ru(III)-NAr3, for complexes 2 and 8, and Ru(II)-NAr3+ for complex 4. a) b) c) 54	  The deconvoluted spectra (Figure 3.7) of the singly oxidized states give insight into the amount of electronic coupling that exists between the ruthenium and the TPA moieties. For all complexes in the singly oxidized state you see a similar decrease in absorption at 440 and 510 nm, with the remarkable differences in absorption at 750 nm attributed to the formation of NAr3Ÿ+. From the most (8) to the least (4) amount of electron density on the ruthenium metal center there is an increasing amount of TPA character (at 750 nm) in the singly oxidized state absorption spectrum, indicating the electronic coupling between the two units in complex can be summarized as 4 > 2 > 8.     700 800 900 1000 11000.00.20.40.60.81.0E1/2=956 mVFractionWavelength (nm) RuII-NAr3 RuIII-NAr3 RuIII-NAr3+E1/2=869 mVDOS of ADB203/TiO2 in 0.5 M LiClO4 CH3CN700 800 900 1000 11000.00.20.40.60.81.0DOS of ADB166/TiO2 in 0.5 M LiClO4 CH3CNE1/2=910 mVFractionPotential (mV vs. NHE) RuII-NAr3 RuIII-NAr3 RuIII-NAr3+E1/2=950 mV800 900 1000 1100 12000.00.20.40.60.81.0E1/2=939 mVDOS of ADB167/TiO2 in 0.5 M LiClO4 CH3CNFractionPotential (mV vs. NHE) RuII-NAr3 RuII-NAr3+ RuIII-NAr3+E1/2=1030 mV  Figure 3.8. The density of states calculations show the fraction (x) of dye molecules of (a) 2/TiO2, (b) 4/TiO2, or (c) 8/TiO2 present in the 2/TiO2, 4/TiO2, or 8/TiO2 (black solid squares), 2+/TiO2, 4+/TiO2, or 8+/TiO2 (red solid circles), and 22+/TiO2, 42+/TiO2, or 82+/TiO2 (green solid triangles) states.   a) b) c) 55	  The standard addition method based on global modeling was used to calculate the fraction of each species present at each applied potential (Figure 3.8). The black solid squares indicate the fraction of dye molecules of 2/TiO2, 4/TiO2, or 8/TiO2 present in the ground state (Ru(II)-NAr3), the red solid circles indicate a singly oxidized species (Ru(III)-NAr3 or Ru(II)-NAr3Ÿ+); 2+/TiO2, 4+/TiO2, or 8+/TiO2, and the doubly oxidized state (Ru(III)-NAr3Ÿ+) is indicated as the green solid triangles; 22+/TiO2, 42+/TiO2, or 82+/TiO2.  This determination of the density of states is feasible once the three reference spectra of the complexes (C) in the C/TiO2, C+/TiO2 and C2+/TiO2 states are obtained (Figure 3.7). Beer’s law can then be used to do a standard addition.                                                              (3.1)  A is the reference spectra matrix, x is the concentration matrix and b is the observed spectra matrix at each applied potential. A least squares minimization is done on x.  Plotting this x matrix versus applied potential results in the density of states.  Overlaid on the data are fits to a modified Nernst equation, given by x = 1/[1 + 10 exp(Eapp − E°)/a × 59 mV], where x is the fraction of molecules present at a given applied potential, a is the nonideality factor, and E° is the formal reduction potential of Ru(III)/Ru(II) or Nar3Ÿ+/0, taken as the applied potential where the concentrations of the oxidized and reduced forms were equal. This data is summarized in Table 3.1. The overlaid fits on the data are to a modified Nernst equation. The Nernst equation has to be modified because this system displays non-Nernstian redox chemistry.  The Nernst equation predicts that for a one-electron transfer process at room temperature, a 59 mV shift in potential should arise when that ratio of the concentrations 56	  of the reduced and oxidized forms are changed by a factor of 10.100 This relation has been successful in fluid electrolyte solution, particularly when activities are used in place of concentrations.100 However, non-Nernstian behavior has been noted at chemically modified electrode surfaces and has been quantified by the inclusion of a nonideality factor, a, into the Nernst equation. Nonideality results when a > 1, behavior most often attributed to intermolecular interactions accompanying the redox chemistry.101,102 It was found that in order to achieve a factor of 10 change in concentration, more than 59 mV of applied potential was needed, and hence, nonideality factors had to be introduced to model all of the interfacial electrochemical data (Figure 3.8).   Table 3.1. Formal Reduction Potentials of Ru(III)/Ru(II) and TPA•+/TPA0 for Complexes 2, 4, and 8 on TiO2 in 0.5 M LiClO4 CH3CN Complex E1/2 (Ru(III)/Ru(II))a E1/2 (TPA•+/0)a 2 910 960 4 1030 940 8 870 960 aPotentials are in mV versus NHE   The reduction potential E1/2 of Ru(III)/Ru(II) or NArŸ+/0 can be determined from the density of states shown in Figure 3.8, as the applied potential where the concentrations of the oxidized and reduced forms were equal. This data is summarized in Table 3.1. For 4/TiO2, TPA was oxidized prior to the ruthenium metal center.  Compounds 2/TiO2 and 8/TiO2 showed intermediate behavior where oxidation of TPA and ruthenium occurred concomitantly. These results are as expected as decreasing the electron density at the metal center stabilizes the ruthenium(II) oxidation. The metal-based Ru(III)/Ru(II) potentials measured by cyclic voltammetry were 250 to 290 mV more positive than that measured for the surface anchored compounds. This observation 57	  can be rationalized by the conversion of the electron-withdrawing carboxylic acid groups to carboxylates upon surface binding.99  3.3. Transient absorption spectroscopy  Nanosecond transient absorption spectroscopy was used to quantify the interfacial charge recombination between TiO2(e-) and the oxidized compound. The data analysis below is based on the hypothesis that interfacial charge recombination of an electron from TiO2 to the oxidized sensitizer has two pathways: interfacial charge recombination of the oxidized metal center and the TiO2 electron (3.2) and interfacial charge recombination of the oxidized TPA moiety and the TiO2 electron (3.3). 	  	  	  	    k1                     (3.2) 	           k2                     (3.3)   The absorption difference spectra of the sensitized materials at indicated time delays after 532 nm laser light excitation (laser irradiance: 1.0 mJ/pulse) are consistent with the formation and loss of one species (Figure 3.9). The increase in absorption at 750 nm was observed after laser excitation consistent with excited-state injection and hole transfer. The prompt appearance after laser excitation of the complexes on TiO2 indicated that both excited state electron injection and hole transfer occurred within 15-20 ns. A progressive increase in size of the absorption band at 750 nm attributed to NArŸ+ was observed upon going from the most electron density on the anionic ring to the least (8 > 2 > 4).       58	   400 500 600 700 800-40-20020ADB203/TiO2 in 0.5 M LiClO4 CH3CNExc. 532 nm; irr. 1.0 mJ/pulseΔ Absorbance (× 10-3 )Wavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 us  400 500 600 700 800-40-2002040Δ Absorbance (× 10-3 )Wavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 usADB166/TiO2 in 0.5 M LiClO4 CH3CNExc. 532 nm; irr. 1.0 mJ/pulse  400 500 600 700 800-0.020.000.020.040.06ADB167/TiO2 in 0.5 M LiClO4 CH3CNExc. 532 nm; irr. 1.0 mJ/pulseΔ AbsorbanceWavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 us  Figure 3.9. Absorption difference spectra measured at indicated time delays after pulsed 532 nm laser light excitation (laser irradiance: 1.0 mJ/pulse) of (a) 8/TiO2, (b) 2/TiO2, or (c) 4/TiO2 immersed in 0.5 M LiClO4/CH3CN solution.   Figure 3.9 shows that there are two processes happening at the decay at 510 nm and at 750 nm. To obtain kinetic data from transient absorption spectroscopy in order to assess the interfacial rates of recombination, the individual processes needed to be deconvoluted. Obtaining the decay associated spectra (DAS) of these two processes requires an analysis of whether the remaining spectra are from one process or not and whether the remaining spectra resemble the expected species. If they do, then kinetic information from the decay associated spectra can be obtained at all wavelengths.  a) b) c) 59	  The most facile procedure to obtain a decay associated spectra is by using a known delta spectrum of one species. For complexes 2 and 8, the Ru(III)-NAr3 spectrum from spectroelectrochemistry was used as the delta spectrum. The kinetic decay at 510 nm was used as the pure kinetic decay for Ru(III)-NAr3 back to the ground state. The transient absorption data was used to subtract the pure Ru(III)-NAr3 spectra at all time delays based on the kinetic decay at 510 nm. A similar method was used for complex 4, but with the Ru(II)-NAr3Ÿ+ spectra from spectroelectrochemistry used as the delta spectrum and the kinetic decay at 750 nm was used as the pure kinetic decay. Figure 3.10 displays the decay associated spectra of Ru(II)-NAr3Ÿ+ for complexes 2 (c) and 8 (a) and Ru(III)-NAr3 for complex 4 (e). The decay associated spectra for the other transient species (Ru(III)-NAr3 for complexes 2 and 8 and Ru(II)-NAr3Ÿ+ for complexes 4) are shown in Figure 3.10. The DAS for the other species are the standard spectra used at different delay times based on the pure kinetic traces.                 60	  400 500 600 700 800-505101520Decay Associated Spectra of RuII-NAr3•+/TiO2(e-) in 0.5 M LiClO4 CH3CN Δ Absorbance (× 10-3 )Wavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 us  400 500 600 700 800-40-20020Decay Associated Spectra of RuIII-NAr3/TiO2(e-) in 0.5 M LiClO4 CH3CN Δ Absorbance (× 10-3 )Wavelength (nm) 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 usADB203 400 500 600 700 80001020Decay Associated Spectra of RuII-NAr3•+/TiO2(e-) in 0.5 M LiClO4 CH3CN Δ Absorbance (× 10-3 )Wavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 us  400 500 600 700 800-40-20020Decay Associated Spectra of RuIII-NAr3/TiO2(e-) in 0.5 M LiClO4 CH3CN Δ Absorbance (× 10-3 )Wavelength (nm) 20 ns 50 ns 100 ns 500  ns 1 us 5 us 50 usADB166 400 500 600 700 800-20-1001020Δ AbsorbanceWavelength (nm) 15 ns 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 usDecay Associated Spectra of RuIII-NAr3/TiO2(e-) in 0.5 M LiClO4 CH3CN   400 500 600 700 8000204060Decay Associated Spectra of RuII-NAr3•+/TiO2(e-) in 0.5 M LiClO4 CH3CN Δ Absorbance (× 10-3 )Wavelength (nm) 20 ns 50 ns 100 ns 500 ns 1 us 5 us 50 usADB167  Figure 3.10. Decay associated spectra of Ru(II)-NAr3Ÿ+ for a) 8/TiO2 and c) 2/TiO2 and Ru(III)-NAr3 for e) 4/TiO2. The standard decay associated spectra of Ru(III)-NAr3 for b) 8/TiO2 d) 2/TiO2 and Ru(II)-NAr3Ÿ+ for f) 4/TiO2. All sensitized thin films were immersed in 0.5 M LiClO4/CH3CN solution.    The decay associated spectra (Figure 3.10) resemble the species determined in spectroelectrochemistry with a change in absorption at 510 nm and 750 nm. It can be a) b) c) d) e) f) 61	  assumed that at each wavelength only one process is occurring consistent with the formation and loss of one state. Therefore, kinetic data can now be obtained. These two wavelengths at 510 nm and 750 nm were chosen to monitor the interfacial charge recombination of TiO2(e-) with the oxidized sensitizers on a linear time scale. These wavelengths represent the charge recombination of Ru(III)-NAr3/TiO2(e-)  Ru(II)-NAr3/TiO2, the interfacial charge recombination between TiO2(e-) and the oxidized ruthenium center, and  Ru(II)-NAr3Ÿ+/TiO2(e-) → Ru(II)-NAr3/TiO2, the interfacial charge recombination between TiO2(e-) and the oxidized NAr3, respectively. Figure 3.11 represents the normalized species associated kinetics at 510 nm and 750 nm on a linear time scale. Figure 3.11 shows the same normalized kinetics on a log time scale. The absorption changes as a function of time were satisfactorily described by the Kohlrausch-Williams-Watts (KWW) model (equation 3.4)103,104 with a fixed βKWW value of 0.19 under all conditions (Figure 3.11, overlay in yellow). 	                                            (3.4) 	  	  	  	  	  	  	  	           62	  0 20 40 60 800.00.20.40.60.81.0β=0.19kcr=5.1×104 s-1kcr=5.4×105 s-1Abs/ NormalizedTime (µs) Corr 750 nm 510 nm  1E-8 1E-7 1E-6 1E-5 1E-40.00.20.40.60.81.0β=0.19kcr=5.1×104 s-1kcr=5.4×105 s-1Abs/ NormalizedTime (s) Corr 750 nm 510 nm  0 20 40 60 800.00.20.40.60.81.0β=0.19kcr=2.0×104 s-1Abs/ NormalizedTime (µs) 510 nm Corr 750 nmkcr=5.2×105 s-1  1E-8 1E-7 1E-6 1E-5 1E-40.00.20.40.60.81.0kcr=2.0×104 s-1kcr=5.2×105 s-1Abs/ NormalizedTime (s) 510 nm Corr 750 nmβ=0.19  0 20 40 60 800.00.20.40.60.81.0Abs/ NormalizedTime (µs) 510 nm 750 nmkcr=6.2×105 s-1kcr=1.7×104 s-1β=0.19  1E-8 1E-7 1E-6 1E-5 1E-40.00.20.40.60.81.0Abs/ NormalizedTime 510 nm 750 nmkcr=6.2×105 s-1kcr=1.7×104 s-1β=0.19  Figure 3.11. The normalized species associated kinetics at 510 nm and 750 nm in a linear time scale representing charge recombination of Ru(III)-NAr3/TiO2(e-) à Ru(II)-NAr3/TiO2 and Ru(II)-NAr3Ÿ+/TiO2(e-) à Ru(II)-NAr3/TiO2 respectively in a) 8/TiO2 c) 2/TiO2 and e) 4/TiO2 after 532 nm laser light excitation (laser irradiance: 1.0 mJ/pulse). Show the same normalized kinetics on a log time scale of 8/TiO2, 2/TiO2 and 4/TiO2 is shown in b), d) and f) respectively. Overlaid on a-f in yellow are KWW fits with a shared beta value of 0.19.  a) b) c) d) e) f) 63	  The time-dependent absorption changes (Figure 3.11) were not superimposable after normalization at their initial amplitudes. This indicates that charge recombination was not the same for all three dyads. The results are summarized in Table 3.2. In the case of all three complexes, charge recombination rate (k2) of TiO2(e-) and the oxidized ruthenium center was the fastest and the charge recombination rate (k1) of TiO2(e-) and the oxidized TPA was slower. This result in itself illustrates that decreased charge recombination rates can be achieved by deconjugation of the cyclometalated ruthenium moiety and the TPA moiety. The retardation of the rate of k1 was most dramatic in complex 4 as expected as it was the only complex to clearly display oxidation of the Ru(III)/Ru(II) redox couple to occur prior to TPA oxidation (Table 3.1). Complex 2 observed a considerable decrease in k1 compared to complex 4 and the lowest reduction in rate of k1 was found in complex 8.   Table 3.2. Charge Recombination Rate Constants of 2/TiO2, 4/TiO2, and 8/TiO2 in 0.5 M LiClO4/CH3CN by KWW Fitting Complex k1 (*105 s-1) k2 (*104 s-1) 2 5.2 2.0 4 6.2 1.7 8 5.4 5.1   It was of interest to calculate the extent of hole transfer from the oxidized ruthenium center to the covalently linked TPA moiety on the basis of the spectroelectrochemical data, as these values can be compared to those measured experimentally after pulsed laser excitation. The hole transfer yields were calculated without the inclusion of nonideality factors. The results are summarized in Table 3.3. To be consistent with the spectroelectrochemical results, the Ru(III)/Ru(II) and NAr3Ÿ+/0 redox reactions were considered to be independent of each other (equation 3.5) even 64	  though these moieties are covalently linked. The equilibrium constants and hole transfer yields were calculated with equations 3.6 and 3.7, respectively. 	                                     (3.5)                                                   (3.6) 	                                               (3.7) 	  	  Three different scenarios are possible for the hole transfer reaction under study. In the first, the driving force for hole transfer is small and Keq << 1. The second scenario occurs when Keq = 1. The third scenario occurs when the driving force for hole transfer is large Keq >> 1. For both complexes 2 and 8, the calculated and experimental, Keq is less than 1, showing that the driving force for hole transfer is small. Specifically the driving force for hole transfer in complex 8 is remarkably close to zero. For complex 4, the Keq is over 1, illustrating that the driving force for hole transfer is large. The quantum yield of hole transfer parallels the calculated and experimentally determined driving force for hole transfer. The quantum yield for hole transfer is effectively double for complex 4 compared to 2 and quadruple for complex 8.   Table 3.3. Calculated and Measured Quasi-Equilibrium Constants at 25 ns Time Delay and Intramolecular Hole Transfer Quantum Yields (Φ) of Complexes on TiO2 in 0.5 M LiClO4/CH3CN after 532 nm Light Excitation Complex Keq,calc Φcalc Keq,meas Φmeas 2 0.21 0.32 0.41 0.39 4 3.5 0.65 7.8 0.74 8 0.030 0.15 0.11 0.25   65	   The quantum yields for hole transfer measured after pulsed laser excitation of the sensitized thin films are in satisfactory agreement with the calculated values. If further calculations were to be done, the inclusion of nonideality factors should broaden the potential range over which Ru(III)/Ru(II) and NAr3Ÿ+/0 redox chemistry occurs, potentially improving the agreement of the values. The extent of hole transfer is in good agreement with the predicted values.   The standard addition method was used to calculate the fraction of each species present as a function of time delay. There is an increasing amount of Ru(III)-TPAŸ+ (red trace, Figure 3.12) going from complex 8 < 2 < 4 consistent with the hole transfer yields.  0 20 40 60 800.00.20.40.60.81.00.0 0.1 0.2 0.3 0.4 0.50.00.20.40.60.81.0FractionTime (µs)FractionTime (µs) RuIII-NAr3 RuII-NAr3+ RuII-NAr3  0 20 40 60 800.00.20.40.60.81.00.0 0.1 0.2 0.3 0.4 0.50.00.20.40.60.81.0FractionTime (µs)FractionTime (µs) RuIII-NAr3 RuII-NAr3+ RuII-NAr3  0 20 40 60 800.00.20.40.60.81.00.0 0.1 0.2 0.3 0.4 0.50.00.20.40.60.81.0FractionTime (µs)FractionTime (µs) RuIII-NAr3 RuII-NAr3+ RuII-NAr3  Figure 3.12. Fractions of Ru(III)-NAr3, Ru(II)-NAr3Ÿ+, and Ru(II)-NAr3 as a function of time delays for 8/TiO2, 2/TiO2, and 4/TiO2. The insets show the early time scale up to 500 ns. a) b) c) 66	  3.4. Summary  The characterization of complexes 2, 4, and 8 on TiO2 has provided new insights into the kinetics and thermodynamics of interfacial electron and hole transfer reactions. The redox chemistry was found to be non-Nernstian in behavior, reasonably attributed to the electric field present at the interface. The charge recombination kinetics were different for all sensitized materials characterized, while the rate of interfacial charge recombination of the TiO2 electron and the TPAŸ+ was the slowest for complex 4. The quantum yield of hole transfer was demonstrated to be the highest in complex 4 following the trend 4 > 2 > 8. Finally, the biggest finding was achieving decreased recombination through reducing the conjugation between the donor and acceptor moieties, proving careful molecular design can slow down charge recombination.   	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  67CHAPTER FOUR: CONCLUSIONS AND FUTURE DIRECTIONS  4.1. Conclusions  The work described in this thesis provides the first analysis of decreased charge recombination rate by modification of the bridging unit of the donor and acceptor moieties on TiO2. Prior to this research, the importance of the bridging ligand between the donor and acceptor moieties has not been emphasized. This work challenges previous arguments that charge recombination is entirely controlled by TiO2 electron diffusion, as careful molecular design can indeed slow down charge recombination.   In Chapter 2 the synthesis of three bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand furnished with terminal triphenylamine substituents are reported. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(tctpy)]. Substitution on the TPA unit was employed to add steric bulk about the TPA-thiophene linkage. EWGs (complex 4; -CF3) and EDGs (complex 8; -OMe) were installed on the anionic ring of the pbpy ligand. The unsubstituted complex was also under study (complex 2; -H). All complexes were synthesized in high yield. HRMS, 1H NMR and 13C NMR spectroscopy, as well as elemental analysis verified the identities and purity of the complexes. The spectroscopic and electrochemical properties of the title complexes were also explored. Comparable to previous literature, it is found that the redox chemistry of the ruthenium center can be independently modulated by placing EWGs or EDGs on the anionic ring of the pbpy ligand. The UV-vis spectrum for each complex is broad (e.g., absorption bands are extended from the UV region to ~800 nm in all cases) and intense (e.g., ε ~ 104 M-1cm-1) because of the overlapping intraligand charge-transfer and metal-to-ligand charge-68	  transfer transitions. Although the molar extinction coefficients are satisfactory, they were significantly decreased in comparison to the complex’s conjugated counterparts as expected.   In Chapter 3 the energetics and kinetics of interfacial charge recombination were investigated through spectroelectrochemistry and transient absorption spectroscopy. When these sensitizers are bound to TiO2 the ability to localize the HOMO proximal or distal to the surface (i.e., to the ruthenium or TPA chromophore) results in an intramolecular hole-transfer quantum yield that can be modulated. Transient absorption spectroscopy indicates that charge recombination was reduced through modification of the bridge with a 33-fold slower rate of interfacial charge recombination for the –CF3 substituted dye as compared to the conjugated counterpart. Therefore, translation of the hole from the ruthenium center to the TPA did inhibit charge recombination through careful molecular design. These fundamental insights into factors that control interfacial charge-transfer events can be used to design better sensitizers for high performance DSSCs.   4.2. Future Directions  In Chapter 3, the rate of interfacial recombination between injected electrons in TiO2 and the oxidized sensitizer were different with all the sensitizers studied illustrating that reducing the conjugation about the bridging unit does affect the rate of recombination. To probe the effects of the spacer unit on the rate of interfacial recombination further, the complexes in Figure 4.1 are proposed.    69	  NNRuNNNCO2HHO2CCO2-SNOMeMeOR1R1R1 = isopropyl, t-butylNNRuNNNCO2HHO2CCO2-NOMeMeOlinker linker = Figure 4.1. Molecular structures of a series of bichromic cycloruthenated complexes with modified spacer units to study interfacial recombination of TiO2 electrons and the oxidized dye. In all cases the HOMO should be localized to the TPA unit.    Another area that could be explored by using a similar molecular scaffold includes photoelectrosynthesis water-splitting cells. Photoelectrosynthesis cells can directly convert solar energy to chemical energy in the form of hydrogen fuels. This device requires a catalyst to mediate the four-electron chemistry associated with water oxidation. As visualized in Figure 4.2 a bichromic dye can be used to create a charge separated state. By systematically modulating the positioning of the holes on the TPA unit, photo-generated holes on the amine moieties to a water oxidation catalyst as a means of coupling single photon absorption events with multi-electron catalysis.   70	  NNSNCCOOOONNNPOOORuCF3TiO2IrOxh+e-hv Figure 4.2. Proposed bichromic cycloruthenated sensitizer for a photoelectrosynthesis cell.   A bichromic dye manifold will be attached to the TiO2 surface with water stable phosphonate linkers, with the opposing end of the molecular platform tethered to IrOx nanoparticles that will serve as water oxidation catalysts. Malonate capping ligands will serve as the bridge between the molecules and the catalyst. Lateral intramolecular hole hopping was observed with this bichromic dye manifold, wherein the hole could hop across the TiO2 surface between two molecules (eq. 4.1).                     (4.1)   This strategy is critical for translating oxidized equivalents to a catalyst after excited state injection. In one scheme for such cells, the hole must hop to an oxidation catalyst after excited state injection.     71	   Figure 4.3. Proposed mechanism for a bichromic cycloruthenated sensitizer in a photoelectrosynthesis cell.   Previously, for the bichromic dye manifold, it was reported that charge recombination occurred on the same time scale as did hole hopping when every sensitizer had been oxidized by one electron.99 To improve on this, a single oxidizing equivalent could circumnavigate a single nanocrystallite once in search of a catalyst before recombination if the rate of recombination was slower than that of hole hopping. Modification of the spacer unit to reduce rates of interfacial recombination, as described in this work, the rate of recombination would occur more slowly than the time scale for hole hopping when every sensitizer would be oxidized by one electron and efficient accumulation at a catalyst could be expected. 	  	  72CHAPTER FIVE: EXPERIMENTAL 5.1. Chapter 2 Preparation of Compounds. Reagents and solvents were commercially available and were used as received. All reactions and manipulations containing MeCN, CH2Cl2, MeOH, DMF, THF were passed through an MBraun solvent purification system prior to use. RuCl3.3H2O was purchased from Pressure Chemical Co., Pittsburgh, PA) and trimethyl-4,4’,4’’-tricarboxylate-2,2’:6’,2’’-terpyridine was purchased from Helios Chemical Co., Ecublens, Switzerland). Purification by column chromatography was carried out using silica (Silicycle: Ultrapure Flash Silica) and alumina (Fisher Chemical: Alumina, Neutral). Analytical thin-layer chromatography was performed on aluminum-backed sheets precoated with silica 60 F254 adsorbent (0.25 mm thick: Silicycle: Ultrapure Silica Gels; Quebec city, Quebec, Canada) and aluminum-backed sheets precoated with aluminum oxide matrix with fluorescent indicator 254 nm (Fluka Analytical: St. Louis, MO, USA) and visualized under UV light. Routine 1H spectra were recorded at 300 and 400 MHz and routine 13C spectra were recorded at 100 MHz on a Bruker AV300 and 400 instrument at ambient temperature. Chemical shifts (δ) are reported in parts per million (ppm) from low to high field and referenced to a residual nondeuterated solvent. Standard abbreviations indicating multiplicity are used as follows: s = singlet; d = doublet, t = triplet, pent = pentet, sept = septet, m = multiplet. All proton assignments correspond to the generic molecular schemes that are provided (Figure 1).   Organic compounds 1-(2-oxo-2-phenylethyl)pyridine-1-ium iodide105, 1-(2-oxo-2-(3-(trifluoromethyl)phenyl)ethyl)pyriidn-1-ium iodide105, 1-(2-(3-methoxypenyl)-2-oxoethyl)pyridine-1-ium iodide105, (E)-3-(5-bromothiophen-2-yl)-1-(pyridine-2-yl)prop-73	  2-en-1-one106, 4-(5-bromothiophen-2-yl)-6-phenyl-2,2’-bipyridine (P4)57, 4-(5-bromothiophen-2-yl)-6-(3-(trifluoromethyl)phenyl-2,2’-bipyridine (P5)56, 4-(5-bromothiophen-2-yl)-6-(3-methoxyphenyl)-2,2’-bipyridine (P7)56, and Ru(L5)Cl338 were prepared as previously reported.   Physical Methods. Elemental analysis (EA), electrospray ionization mass spectrometry (ESI-MS), matrix-assisted laser desorption/ ionization mass spectrometry data were collected at the Chemistry Instrumentation Facility of the University of British Columbia. Electrochemical analysis was performed under anaerobic conditions with a Princeton Applied Research VersaStat 3 potentiostat using dry solvents, platinum working and counter electrodes, a silver pseudoreference electrode, and a 0.1 M NBu4BF4 supporting electrolyte. Electronic spectroscopic data were collected using a Perkin Elmer UV-vis spectrophotometer (Lambda 35).  Computational Methods. The Gaussian 03 computational package107 to perform ground-state geometry optimization calculations employing Becke’s three-parameter hybrid exchange functional, the Lee-Yang-Parr non-local correlation functional B3LYP,108,109 and SDD basis set110,111 with an effective core potential, was used for the Ru atom and a 6-31 G* basis set was used for C, H, N, P, and Cl atoms.112 Time-dependent density functional theory (TDDFT) calculations were also performed using this methodology, and the first 60 singlet excited states were calculated. Calculations by the first-principles method were used to obtain accurate excitation energies and oscillator strengths. We modeled the solvent with the polarizable continuum model using MeOH as the solvent.113,114 74	    NNRuNNNCO2HHO2CCO2HSNOMeMeOR1R2 a bcdefghijklmopq rnABC D EComplexesNNSNOMeMeOR1R2abcdefghijklmn opqDonor LigandsNNSBrR1R2abcdefgmn opqrNOMeMeOhijklsPrecursors+1 Figure 5.1. Labeling scheme for 1H NMR signal assignments.   Preparation of Precursors. N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (P1).  3,5-Dimethylaniline (2 mL, 16.0 mmol), 4-iodoanisole (9.39 g, 40.1 mmol), 18-crown-6 (0.848 g, 3.21 mmol), copper powder(4.08 g, 64.2 mmol), K2CO3 (17.73 g, 128 mmol) were suspended in o-dichlorobenzene and refluxed for 72 h under nitrogen. The resulting heterogeneous solution was cooled to room temperature and 100 mL EtOAc was added. The solid was removed by filtration and discarded. The solvent was removed from the filtrate by vacuum distillation and the resultant oil was purified by column chromatography (SiO2: Pet. Ether/ CH2Cl2, 1:1, Rf= 0.18). The desired fraction was collected, isolated and the solvent was removed in vacuo. The solid was recrystallized in MeOH to yield 4.40 g (82%) of a colorless solid. 1H NMR (300 MHz, CDCl3): δ = 7.07 (d, 4H, 3J = 9.0 Hz, Hk), 6.84 (d, 4H, 3J = 9.0 Hz, Hj), 6.62 (s, 2H, Hi), 6.58 (s, 1H, Hs), 3.82 (s, 6H, Hl), 2.23 (s, 6H, Hh) 13C NMR (100 MHz, CDCl3): δ = 155.6, 148.9, 141.6, 138.6, 126.4, 122.9, 119.2, 114.68, 55.6, 21.5; HRMS (ESI): m/z = 334.1813 [(MH)+] 75	  (calcd for C22H24NO2 : m/z = 334.1807). Anal. Calcd for C22H23NO2: C, 79.25; H, 6.95; N, 4.20. Found: C, 78.95; H, 7.04; N, 4.08. NOMeMeOhijkls   4-Bromo-N,N-bis(4-methoxyphenyl)3,5-dimethylaniline (P2). To a cooled mixture (0°C) of P1 (0.200 g, 0.599 mmol) in EtOAc (5 mL), NBS (0.107 g, 0.599 mmol) was added. The reaction mixture was allowed to warm to room temperature and was then stirred in the dark for 16 h. The organic layer was washed with 3 x 15 mL water, dried over MgSO4, the solution was filtered and evaporated in vacuo. The solid was recrystallized in MeOH to yield 2.02g (81%) of a colorless solid. 1H NMR (300 MHz, CDCl3): δ = 7.00 (d, 4H, 3J = 8.5 Hz, Hk), 6.81 (d, 4H, 3J = 8.9 Hz, Hj), 6.65 (s, 2H, Hi), 3.80 (s, 6H, Hl), 2.27 (s, 6H, Hh). 13C NMR (100 MHz, CDCl3): δ =155.9, 147.4, 141.0, 138.7, 126.5, 120.9, 118.5, 114.8, 55.6, 24.0. HRMS (ESI): m/z = 412.0922 [(MH)+] (calcd for C22H23BrNO2+: 412.0912). Anal. Calcd for C22H22BrNO2 : C, 64.09; H, 5.38; N, 3.40. Found: C, 64.20; H, 5.46; N, 3.35. NOMeMeOhijklBr    N-N-bis(4-methoxyphenyl)3,5-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline (P3). A Schlenk flask was charged with Pd(dppf)Cl2. CH2Cl2 (0.198 g, 0.243 76	  mmol), KOAc (0.357 g, 0.364 mmol) and bis(pinacolato)diboron (0.678 g, 2.67 mmol) and flushed with nitrogen. DMSO (9.6 mL, stored over molecular sieves and degassed thoroughly with nitrogen before use) and P2 (0.50 g, 1.27 mmol) were then added. The reaction mixture was stirred at 80°C for 16 h under nitrogen. The mixture was allowed to cool to room temperature and CH2Cl2 (50 mL) was added to the reaction mixture. The CH2Cl2-DMSO mixture was washed with water (3 x 100mL), dried over MgSO4, and filtered. The brown solid left upon removal of solvent was solubilized in CH2Cl2 and preabsorbed on silica. The solvent was removed and the sample was purified by column chromatography [SiO2: Pet. Ether: CH2Cl2, 9:1, Rf = 0.27] to yield 0.180 g (32%) of the product as a colorless solid. The compound was used without further characterization due to instability outlined in the Appendix C.   NOMeMeOBOO  1-(2-oxo-2-phenylethyl)pyridine-1-ium iodide. Following a previously published  procedure115, acetophenone (2.0 mL, 17.1 mmol) and crystalline iodine (4.34 g, 17.1 mmol) were solubilized in pyridine (12.4 mL) and refluxed for 1 h. The solution was cooled to room temperature and a brown precipitate formed. The reaction mixture was poured into an excess of Et2O where it formed a light brown precipitate. The solid was collected and recrystallized from EtOH to yield 3.72 g (67%) of a brown crystalline solid. The 1H NMR spectrum resembled that previously reported in literature. 77	  NOI   1-(2-oxo-2-(3-(trifluoromethyl)phenyl)ethyl)pyridine-1-ium iodide. Following a previously published procedure,116 1-(3-(trifluoromethyl)phenyl)ethan-1-one (0.41 mL, 2.66 mmol) and crystalline iodine (0.675 g, 2.66 mmol) were solubilized in pyridine (2.0 mL) and refluxed for 5 h. The mixture was cooled to room temperature and a brown precipitate formed. The reaction mixture was poured into an excess of Et2O where it formed a light brown precipitate. The solid was collected and recrystallized from EtOH to yield 1.02 g (98%) of a brown crystalline solid. The 1H NMR spectrum resembled that previously reported in literature. NOIF3C   1-(2-(3,5-bis(trifluoromethyl)phenyl)-2-oxoethyl)pyridinium iodide. This compound was prepared via a modified literature procedure.117 1-(3,5-bis(trifluoromethyl)phenyl)ethanone (2.0 mL, 11.1 mmol) and crystalline iodine (2.32 g, 11.1 mmol) were solubilized in pyridine (8.1 mL), refluxed for 1 h and then cooled to room temperature. Upon cooling a brown precipitate formed and the precipitate and reaction mixture were added in portions to an excess of Et2O where it formed a light brown precipitate. The solid was collected and recrystallized from EtOH to yield 4.63 g (90%) of a brown crystalline solid. The identity was confirmed through comparison of the 1H NMR spectrum.  78	  NOF3CICF3    1-(2-(3-methoxyphenyl)-2-oxoethyl)pyridine-1-ium iodide. Following  a previously published procedure,105 1-(3-methoxyphenyl)ethan-1-one (3.0 mL, 21.9 mmol) and crystalline iodine (5.82 g, 22.9 mmol) were solubilized in pyridine (14 mL) and refluxed for 1 h. The solution was cooled to room temperature where a brown precipitate formed. The reaction mixture was added to an excess of Et2O, forming a light brown precipitate. The solid was collected and recrystallized in EtOH to yield 6.07 g (78%) of a brown crystalline solid. The identity was confirmed through comparison of the 1H NMR spectrum.  NOMeOI    4-(5-bromothiophen-2-yl)-6-phenyl-2,2’-bipyridine (P4). Following a previously published procedure,57 a mixture of 1-(2-oxo-2-phenylethyl)pyridinium iodide (2.74 g, 8.41 mmol), (E)-3-(5-bromothiophen-2-yl)-1(pyridine-2-yl)prop-2-en-1-one (2.48 g, 8.41 mmol) and ammonium acetate (16.86 g, 218 mmol) were refluxed in formamide (62 mL) for 18 h. The resulting heterogeneous solution was cooled to room temperature. The solid was removed by filtration, dried, and triturated with MeOH. The product was dried in vacuo to give 1.03 g (31%) of a light brown solid. The 1H NMR spectrum resembled that of previously reported literature.  79	  NNSBr   4-(5-bromothiophen-2-yl)-6-(3-(trifluoromethyl)phenyl)-2,2’-bipyridine (P5). Following a previously published procedure,56 a mixture of 1-[2-oxo-2-[3-(trifluoromethyl)phenyl]ethyl]pyridinium iodide (1.55 g, 4.00 mmol), (E)-3-(5-bromothiophen-2-yl)-1(pyridine-2-yl)prop-2-en-1-one ( 1.16 g, 4.00 mmol), and ammonium acetate (7.91 g, 102 mmol) were refluxed in formamide (29 mL) for 18 h. The resulting heterogeneous solution was cooled to room temperature. The solid was removed by filtration, dried, and triturated with MeOH. The product was dried in vacuo to give 1.32 g (73%) of a light brown solid. The 1H NMR spectrum resembled that previously reported in literature. NNSBrF3C   6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine (P6). A mixture of 1-(2-(3,5-bis(trifluoromethyl)phenyl)-2-oxoethyl)pyridinium iodide (0.908 g, 2.72 mmol), (E)-3-(5-bromothiophen-2-yl)-1(pyridine-2-yl)prop-2-en-1-one (0.799 g, 2.72 mmol), and ammonium acetate (5.44 g, 70.6 mmol) were refluxed in formamide (20 mL) for 18 h. The resulting heterogeneous solution was cooled to room temperature. The solid was removed by filtration, dried, and triturated with MeOH. The product was dried 80	  in vacuo to yield 552 mg (38%) of a light brown solid. 1H NMR (300 MHz, CDCl3): δ = 8.74 (ddd, 1H, 3J = 4.8 Hz, 4J = 1.9 Hz, 5J = 0.8 Hz, Ha), 8.65 (d, 1H, 3J = 1.5 Hz, He), 8.60-8.58 (m, 3H, Hd, Hn, Hr), 7.97 (s, 1H, Hp), 7.91 (td, 1H, 3J = 7.8 Hz, 4J = 1.7 Hz, Hc), 7.86 (d, 1H, 4J = 1.6 Hz, Hm), 7.50 (d, 1H, 3J = 3.9 Hz, Hf), 7.40 (ddd, 1H, 3J = 7.8 Hz, 3J = 4.8 Hz, 4J = 1.2 Hz, Hb), 7.17 (d, 1H, 3J = 4.0 Hz, Hg). 13C{1H} NMR (100 MHz, CDCl3): δ = 157.3, 155.3, 154.3, 149.4, 143.1, 142.6, 141.2, 137.2, 132.3 (q, 2JCF = 33.0 Hz), 131.5, 127.2 (br s), 126.4, 124.6, 123.5 (q, 1JCF = 273.6 Hz), 122.8 (sept, 3JCF = 3.8 Hz), 121.6, 116.8, 116.3, 115.0. Anal. Calcd for C22H11BrF6N2S: C, 49.92; H, 2.09; N, 5.29. Found: C, 50.20; H, 2.24; N, 5.33.  NNSBrCF3CF3abcdefgmnpr   4-(5-bromothiophen-2-yl)-6-(3-methoxyphenyl)-2,2’-bipyridine (P7). Following a previously published procedure,56 a mixture of 1-(2-(3-methoxyphenyl)-2-oxoethyl)pyridine-1-ium iodide (1.50 g, 6.57 mmol), (E)-3-(5-bromothiophen-2-yl)-1(pyridine-2-yl)prop-2-en-1-one (1.93 g, 6.57 mmol) and ammonium acetate (13.15 g, 171 mmol) were refluxed in formamide (48 mL) for 16 h. The resulting heterogeneous solution was cooled to room temperature. The solid was collected, dried and triturated with MeOH. The product was collected and dried to yield 1.59 g (57%) of a light brown solid. The 1H NMR spectrum resembled that previously reported in literature.  81	  NNSBrMeO   Preparation of Ligands L1-L4. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L1). P3 (0.450 g, 0.979 mmol) and P4 (0.350 g, 0.891 mmol) were solubilized in a THF/ water solution (9:1; 85 mL) and sparged for 10 min with N2. K2CO3 (0.714 g, 5.16 mmol) and Pd(PPh3)4 (0.103 g, 0.0891 mmol) were added, and the reaction was refluxed for 14 h under nitrogen. The reaction mixture was then cooled, and the THF layer was washed with brine. The organic fractions were collected and dried with MgSO4, filtered, and the solvent was removed in vacuo. The resulting oil was then solubilized in CH2Cl2/EtOAc (9.5:0.5) and purified by column chromatography (Al2O3: CH2Cl2/EtOAc, 9.5: 0.5, Rf = 0.20) to yield 0.201 g (35%) as a bright yellow powder.1H NMR (300 MHz, CDCl3): δ = 8.73 (ddd, 1H, 3J = 4.9, 4J = 1.9, 5J = 0.8, Ha), 8.67 (d, 1H, 3J = 6 Hz, Hd), 8.63 (d, 1H, 4J = 3 Hz, He), 8.20 (d, 2H, 3J = 9 Hz, Hn), 7.95 (d, 1H, 4J = 1.6 Hz, Hm), 7.87 (td, 1H, 3J = 7.9 Hz, 4J = 1.7 Hz, Hc), 7.69 (1H, 3J = 3.6 Hz, Hf), 7.54 (t, 2H, 3J = 7.3 Hz, Ho), 7.46 (t, 1H, 3J = 7.0 Hz, Hp), 7.35 (ddd, 1H, 3J = 7.6 Hz, 3J = 4.8 Hz, 4J = 1.2 Hz, Hb), 7.11 (d, 4H, 3J = 9.0 Hz, Hk), 6.88-6.85 (m, 5H, Hg, Hj), 6.67 (s, 2H, Hi), 3.82 (s, 6H, Hl), 2.10 (s, 6H, Hh). 13C NMR (100 MHz, CDCl3): δ = 157.4, 156.5, 156.4, 156.1, 149.2, 148.8, 144.3, 143.6, 141.6, 140.9, 139.5, 139.0, 137.1, 129.3, 128.9, 128.4, 127.2, 127.1, 125.8, 125.3, 124.0, 121.7, 118.8, 116.7, 115.7, 114.9, 55.6, 21.2. Anal. Calcd for C42H35N3O2S: C, 78.11; H, 5.46; N, 6.51. 82	  Found: C, 77.99; H, 5.49; N, 6.42. HRMS (ESI): m/z = 646.2528 [(MH)+] (calcd for C42H36N3O2S+: m/z = 646.2623). rNNSNOMeMeOabcdefghijklmnopq   N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline (L2). P3 (0.383 g, 0.835 mmol) and P5 (0.350 g, 0.759 mmol) were solubilized in a THF/ water solution (9:1; 65 mL) and sparged for 10 min with N2. K2CO3 (0.608 g, 4.40 mmol) and Pd(PPh3)4 (0.088 g, 0.0759 mmol) were added, and the reaction was refluxed for 14 h under nitrogen. The reaction mixture was then cooled, and the THF layer was washed with brine. The organic fractions were collected and dried with MgSO4, filtered, and the solvent was removed in vacuo. The resulting oil was then solubilized in pet. ether/EtOAc (9:1) and purified by column chromatography (SiO2: pet. ether/EtOAc, 9:1, Rf = 0.18) to yield 0.105 g (19%) as a bright yellow powder. 1H NMR (300 MHz, CDCl3): δ = 8.74 (ddd, 1H, 3J = 4.9 Hz, 4J = 1.8 Hz, 5J = 0.8 Hz, Ha), 8.67 (d, 1H, 4J = 1.5 Hz, He), 8.64 (dt, 1H, 3J = 8.0 Hz, 4J = 0.8 Hz, Hd), 8.46 (s, 1H, Hn), 8.36 (d, 1H, 3J = 7.6 Hz, Hr), 7.95 (d, 1H, 4J = 1.6 Hz, Hm), 7.89 (dt, 1H, 3J = 7.8 Hz, 4J = 1.8 Hz, Hc), 7.73-7.71 (m, 2H, Hf, Hp), 7.65 (t, 1H, 3J = 7.8 Hz, Hq), 7.37 (ddd, 1H, 3J = 7.7 Hz, 3J = 4.8 Hz, 4J = 1.1 Hz, Hb), 7.11 (d, 4H, 3J = 9.0 83	  Hz, Hk), 6.90-6.85 (m, 5H, Hg, Hj), 6.67 (s, 2H, Hi), 3.82 (s, 6H, Hl), 2.11 (s, 6H, Hh). 13C {1H} NMR (100 MHz, CDCl3): δ = 156.8, 156.1, 156.0, 155.8, 149.3, 148.8, 144.7, 144.0, 141.2, 140.9, 140.3, 139.0, 137.1, 131.3 (q, 2JCF = 32.2 Hz), 130.4, 129.3, 128.5, 127.1, 126.1, 125.8 (q, 3JCF = 3.6 Hz), 125.1, 124.2, 124.0 (q, 3JCF = 3.8 Hz), 123.0, 121.6, 118.8, 116.6, 116.3, 114.9, 55.6, 21.2. HRMS (ESI): m/z = 714.2401 [(MH)+] (calcd for C43H35F3N3O2S+: m/z = 714.2402). Anal. Calcd for C43H34F3N3O2S: C, 72.35; H, 4.80; N, 5.89. Found: C, 72.39; H, 5.16; N, 5.58.  rNNSNOMeMeOabcdefghijklmnpqCF3  4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). Proligands: P3 (0.426g, 0.927 mmol) and P6 (0.446 g, 0.843 mmol) were solubilized in a THF/ water solution (9:1; 77 mL) and sparged for 10 min with N2. K2CO3 (0.675 g, 4.89 mmol) and Pd(PPh3)4 (0.0974 g, 0.0843 mmol) were added, and the reaction was refluxed for 14 h under nitrogen. The reaction mixture was then cooled, and the THF layer was washed with brine. The organic fractions were collected and dried with MgSO4, filtered, and the solvent was removed in vacuo. The resulting oil was then solubilized in pet. ether/EtOAc (9:1) and purified by column chromatography (SiO2; Pet. ether/EtOAc, 9:1, Rf = 0.19) to yield 0.471 g (71%) as a bright yellow powder. 1H NMR (300 MHz, CDCl3): δ = 8.76-8.73 (m, 2H, Ha, He), 84	  8.63-8.60 (m, 3H, Hd, Hn), 7.97-7.96 (m, Hm, Hp), 7.91 (td, 1H, 3J = 7.7 Hz, 4J = 1.8 Hz, Hc), 7.74 (d, 1H, 3J = 3.6 Hz, Hf), 7.39 (ddd, 1H, 3J = 7.7 Hz, 3J = 4.8 Hz, 4J = 1.0 Hz, Hb), 7.11 (d, 4H, 3J = 9.0 Hz, Hk), 6.91 (d, 1H, 3J = 3.7 Hz, Hg), 6.86 (d, 4H, 3J = 9.0 Hz, Hj), 3.82 (s, 6H, Hl), 2.11 (s, 6H, Hh). 13C {1H} NMR (100 MHz, CDCl3): δ = 157.1, 156.1, 155.6, 154.1, 149.3, 148.9, 145.1, 144.3, 141.5, 140.9, 140.8, 138.9, 137.2, 132.2 (q, 2JCF = 33.4 Hz), 128.6, 127.1, 126.4, 125.0, 124.4, 123.6 (q, 1JCF = 272.9 Hz), 122.7 (sept, 3JCF = 3.6 Hz), 121.6, 118.8, 117.0, 116.6, 114.9, 55.6, 29.8, 21.2. HRMS (ESI): m/z = 782.2281 [(MH)+] (calcd for C44H34F6N3O2S+: m/z = 782.2276). Anal. Calcd for C44H33F6N3O2S: C, 67.60; H, 4.25; N, 5.37. Found: C, 67.66; H, 4.33; N, 5.26. rNNSNOMeMeOabcdefghijklmnpCF3CF3   N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline  (L4). Proligands P3 (0.250 g, 0.495 mmol) and P7 (0.209 g, 0.495 mmol) were solubilized in a THF/ water solution (9:1; mL) and sparged for 10 min with N2. K2CO3 (0.397 g, 2.87 mmol) and Pd(PPh3)4 (0.057 g, 0.0495 mmol) were added, and the reaction was refluxed for 48 h under nitrogen. The reaction mixture was cooled, and the THF layer was washed with brine. The organic fractions were collected and dried with MgSO4, filtered, and the solvent was removed in vacuo. The resulting oil was then solubilized in CH2Cl2/EtOAc (9:1) and purified by column chromatography (Al2O3: CH2Cl2/EtOAc, 9:1, Rf = 0.17) to 85	  yield 0.0860 g (26%) as a bright yellow powder. 1H NMR (300 MHz, CDCl3): δ = 8.73 (ddd, 1H, 3J = 4.8 Hz, 4J = 1.8 Hz, 5J = 0.8 Hz, Ha), 8.67-8.63 (m, 2H, Hd, He), 7.93 (d, 1H, 4J = 1.5 Hz, Hm), 7.87 (td, 1H, 3J = 7.8 Hz, 4J = 1.7 Hz, Hc), 7.79 (m, 1H, Hn), 7.74 (dt, 1H, 3J = 8.1 Hz, 4J = 1.3 Hz, Hr), 7.70 (d, 1H, 3J = 3.6 Hz, Hf), 7.44 (t, 1H, 3J = 7.9 Hz, Hq), 7.35 (ddd, 1H, 3J = 7.5 Hz, 3J = 4.8 Hz, 4J = 0.8 Hz, Hb), 7.11 (d, 4H, 3J = 9.0 Hz, Hk), 7.02 (ddd, 1H, 3J = 8.2 Hz, 4J = 2.6 Hz, 4J = 0.7 Hz, Hp), 6.88-6.84 (m, 5H, Hg, Hj), 6.66 (s, 2H, Hi), 3.94 (s, 3H, Ho), 3.81 (s, 6H, Hl), 2.10 (s, 6H, Hh). 13C {1H} NMR (100 MHz, CDCl3): δ = 160.2, 157.2, 156.3, 156.1, 149.1, 148.8, 144.4, 143.6, 141.5, 141.0, 140.9, 139.0, 137.1, 129.9, 128.4, 127.1, 125.2, 124.0, 121.7, 121.7, 119.6, 118.8, 116.8, 115.8, 114.9, 114.8, 112.9, 100.1, 55.6, 31.1, 21.2. HRMS (ESI): m/z = 676.2643 [(MH)+] (calcd for C43H38N3O3S+: m/z = 676.2634). Anal. Calcd for C43H37N3O3S: C, 76.42; H, 5.52; N, 6.22. Found: C, 76.59; H, 5.56; N, 5.95. rNNSNOMeMeOabcdefghijklmnpOMeq   Preparation of Methyl Ester Complexes. [Ru(L1)(L5)]NO3 (1). A MeOH/H2O/THF (109 mL, 5:1:1 v/v/v) solution containing L1 (0.100 g, 0.155 mmol), L5 (0.095 g, 0.155 mmol) and N-ethylmorpholine (0.25 mL) was sparged for 10 min with N2. Following a 16 h reflux, AgNO3 (0.099 g, 0.501 mmol) was added to the reaction mixture, and the resulting mixture was then left to reflux for an additional 1.5 h. The mixture was cooled 86	  to room temperature and the solvent was removed in vacuo. The resulting oil was solubilized in CH2Cl2/MeOH (9.5:0.5) and purified by column chromatography (SiO2: CH2Cl2/MeOH, 9.5:0.5, Rf = 0.29) to yield 0.128 g (72%) as a deep red fine solid. The product was used without further characterization. HRMS (ESI): m/z = 1153.2526 [(M)+] (calcd for C63H51N6O8RuS+: m/z = 1153.2533). NNRuNNNCO2MeMeO2CCO2MeSNOMeMeO   [Ru(L2)(L5)]NO3 (3). A MeOH/H2O/THF (136 mL, 5:1:1 v/v/v) solution containing L2 (0140 g, 0.196 mmol), L5 (0.121 g, 0.196 mmol) and N-ethylmorpholine (0.25 mL) was sparged for 10 min with N2. Following a 16 h reflux, AgNO3 (0.125 g, 0.735 mmol) was added to the reaction flask, and the resulting mixture was then refluxed for an additional 1.5 h. The mixture was cooled to room temperature and the solvent was removed in vacuo. The resulting oil was solubilized in CH2Cl2/MeOH (9.5:0.5) and purified by column chromatography (Al2O3: CH2Cl2/MeOH, 9.5:0.5, Rf = 0.57) to yield 0.080 g (40%) as a deep red fine solid. The product was used without further characterization. HRMS (ESI): m/z = 1221.2410 [(M)+] (calcd for C64H50F3N6O8RuS+: m/z = 1221.2406). 87	  NNRuNNNCO2MeMeO2CCO2MeSNOMeMeOF3C  [Ru(L4)(L5)]NO3 (7). A MeOH/H2O/THF (56 mL, 5:1:1 v/v/v) solution containing L4   (0.055 g, 0.0813 mmol), L5 (0.0500 g, 0.0813 mmol) and N-ethylmorpholine (0.1 mL) was sparged for 10 min with N2. Following a 16 h reflux, AgNO3 (0.0520 g, 0.305 mmol) was added to the reaction flask, and the resulting mixture was then left to reflux for an additional 1.5 h. The mixture was then cooled to room temperature and the solvent was removed in vacuo. The resulting oil was solubilized in CH2Cl2/MeOH (9.5:0.5) and purified by column chromatography (Al2O3: CH2Cl2/MeOH, 9.5:0.5, Rf = 0.75) to yield 0.080 g (83%) as a deep red fine solid. The product was used without further characterization. HRMS (ESI): m/z = 1183.2633 [(M)+] (calcd for C64H53N6O9RuS+: m/z = 1183.2628). 88	  NNRuNNNCO2MeMeO2CCO2MeSNOMeMeO+1MeO  Preparation of Acid Complexes. [Ru(L1)(L5)]NO3 (2). A flask containing compound 1 (0.120 g, 0.104 mmol) was suspended in 15 mL of a DMF/NEt3/H2O (3:1:1 v/v/v) solution and refluxed under N2 overnight. The solvent was then removed under reduced pressure, and the resultant solid was washed with Et2O, hexanes, and CH2Cl2, respectively to yield 104 mg (90 %) of the product as a deep black microcrystalline solid. 1H NMR (300 MHz, MeOD): δ = 9.23 (s, 2H, HE), 9.01 (s, 2H, HD), 8.80 (s, 1H, He), 8.75 (d, 1H, 3J = 8.3 Hz, Hd), 8.52 (s, 1H, Hm), 8.14 (d, 1H, 3J = 3.7 Hz, Hf), 7.97-7.90 (m, 3H, Hc, Hg, Hn), 7.66 (d, 2H, 3J = 5.8 Hz, HA), 7.59 (d, 2H, 3J = 5.8 Hz, HB), 7.46 (d, 1H, 3J = 5.0 Hz, Ha), 7.14-7.05 (m, 5H, Hb, Hk), 6.92 (d, 4H, 3J = 9.0 Hz, Hj), 6.77 (t, 1H, 3J = 7.4 Hz, Ho), 6.68 (s, 2H, Hi), 6.50 (t, 1H, 3J = 7.3 Hz, Hp), 5.58 (d, 1H, 3J = 7.4 Hz, Hq), 3.81 (s, 6H, Hl), 2.69 (s, 6H, Hh). LRMS (MALDI-TOF): m/z = 1111.3 [(M)]+ (calcd for C60H45N6O8RuS+: m/z = 1111.2). Anal. Calcd for C60H45N7O11RuS. 4H2O: C, 57.87; H, 4.29; N, 7.87. Found: C, 58.00; H, 4.29; N, 7.80. 89	  NNRuNNNCO2HHO2CCO2HSNOMeMeOa bcdefghijklmpqnABC D E+1o  [Ru(L2)(L5)]NO3 (4). Compound 3 (0.050 g, 0.0409 mmol) was dissolved in a DMF/H2O/NEt3 (3:1:1; 6 mL) solution and refluxed overnight. The solvent was then removed under reduced pressure, and the resultant solid was washed successively with Et2O, pet. ether, CH2Cl2 to yield 42 mg (88%) of the product as a deep microcrystalline solid. 1H NMR (300 MHz, MeOD): δ = 9.23 (s, 2H, HE), 9.00 (s, 2H, HD), 8.83 (d, 1H, 4J = 1.2 Hz, He), 8.77 (d, 1H, 3J = 8.2 Hz, Hd), 8.66 (s, 1H, Hm), 8.21-8.19 (m, 2H, Hf, Hn), 7.94 (t, 1H, 3J = 7.8 Hz, Hc), 7.62-7.56 (m, 4H, HA, HB), 7.50 (d, 1H, 3J = 5.0 Hz, Ha), 7.15 (t, 1H, 3J = 6.3 Hz, Hb), 7.09-7.05 (m, 5H, Hg, Hk), 6.91 (d, 4H, 3J = 9.0 Hz, Hj), 6.74 (d, 1H, 3J = 7.9 Hz, Hp), 6.69 (s, 2H, Hi), 5.88 (d, 1H, 3J = 7.9 Hz, Hq), 3.81 (s, 6H, Hl), 2.70 (s, 6H, Hh). LRMS (MALDI-TOF): m/z = 1179.2 [(M)]+ (calcd for C61H44F3N6O8RuS+: m/z = 1179.2). Anal. Calcd for C61H44F3N6O8RuS. 2H2O: C, 60.29; H, 3.98; N, 6.92. Found: C, 60.56; H, 4.02; N, 6.98. 90	  NNRuNNNCO2HHO2CCO2HSNOMeMeOF3Ca bcdefghijklmpqnABC DE+1  [Ru(L4)(L5)]NO3 (8). Compound 7 (0.0720 g, 0.0609 mmol) was dissolved in a DMF/H2O/NEt3 (3:1:1; 9 mL) solution and refluxed overnight. The solvent was then removed under reduced pressure, and the resultant solid was washed successively with Et2O, pet. ether, CH2Cl2 to yield 54 mg (78%) of the product as a deep black microcrystalline solid. 1H NMR (300 MHz, MeOD): δ = 9.27 (s, 2H, HE), 9.03 (s, 2H, HD), 8.76 (s, 1H, He), 8.71 (d, 1H, 3J = 8.3 Hz,  Hd), 8.58 (s, 1H, Hm), 8.15 (d, 1H, 3J = 3.7 Hz, Hf), 7.89 (td, 1H, 3J = 7.8 Hz, 4J = 1.0 Hz, Hc), 7.73–7.69 (m, 3H, HA, Hn), 7.65 (dd, 2H, 3J = 5.8 Hz, 4J = 1.6 Hz, HB) 7.21 (d, 1H, 3J = 5.7 Hz, Ha), 7.12-7.06 (m, 6H, Hb, Hg, Hk), 6.91 (d, 4H, Hj), 6.82 (t, 1H, 3J = 8.0 Hz, Ho), 6.68 (s, 2H, Hi), 6.07 (d, 1H, 3J = 8.0 Hz, Hp), 3.81 (s, 6H, Hl), 2.82 (s, 3H, Hq), 2.16 (s, 6H, Hh). LRMS (MALDI-TOF): m/z = 1141.2 [(M)]+ (calcd for C61H47N6O9RuS+: m/z = 1141.2). Anal. Calcd for C61H47N6O9RuS. 2H2O: C, 62.24; H, 4.37; N, 7.14. Found: C, 62.52; H, 4.58; N, 7.09.  91	  NNRuNNNCO2HHO2CCO2HSNOMeMeOa bcdefghijklmopqnABC DE+1MeO	  	   5.2. Chapter 3.  Spectroelectrochemical Methods. Spectroelectrochemical measurements were obtained with an apparatus similar to that previously described.99 A potentiostat (BAS model CV-50W) was employed for measurements in a standard three-electrode arrangement with a sensitized TiO2 thin film deposited on an FTO substrate working electrode, a platinum disk counter electrode, and a Ag/AgCl reference (Bioanalytical Scientific Instruments, Inc.) in acetonitrile containing 0.5 M LiClO4. All potentials are reported versus the normal hydrogen electrode (NHE). The ferrocenium/ferrocene (Fc+/Fc) half-wave potential was measured at room temperature before and after each experiment and was used as an external standard to calibrate the reference electrode. A conversion constant of -630 mV from NHE to Fc+/Fc was used in acetonitrile at 25°C.118 Steady-state UV-vis absorption spectra were recorded in concomitant with bulk electrolysis of a standard three-electrode cell. External biases were applied to the sensitized TiO2 thin film deposited on an FTO substrate working electrode positioned diagonally in a 1 cm cuvette. 92	  Each potential step was held for around 2 to 3 minutes until the spectrum was invariant with time and the next potential was applied.   Transient Absorption Spectroscopy. Nanosecond transient absorption measurements were obtained with an apparatus similar to that previously described.99 Samples were photoexcited by a frequency-doubled, Q-switched, pulsed Nd:YAG laser [Quantel USA (formerly Big Sky Laser Technologies) Brilliant B, 532 nm, 5-6 ns full width at half-maximum (fwhm), 1 Hz, ~10 mm in diameter] directed 45° to the film surface. A 150 W xenon arc lamp coupled to a ¼ m monochromator (Spectral Energy Corp., GM 252) served as the probe beam (Applied Photophysics), which was aligned orthogonally to the excitation light. For detection at sub-100 µs time scales, the lamp was pulsed with 80 V. Detection was achieved with a monochromator (Spex 1702/04) optically coupled to an R928 photomultiplier tube (Hamamatsu). Transient data were acquired on a computer-interfaced digital oscilloscope (LeCroy 9450, dual 350 MHz). 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Tetrahedron 66, 918–929.                                         99	  APPENDIX A: SPECTRAL DATA   10001234567891 01 11 21 3f1  (ppm)- 2 0 0 0 0- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 56.056.060.981.924.054.002.233.826.586.626.826.836.846.866.866.877.047.057.067.077.087.09Figure A.1. N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (P1). 1H NMR (300 MHz, CDCl3, 298K). 10102 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)- 5 0 0 0 005 0 0 0 01 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 54 E+ 0 54 E+ 0 54 E+ 0 55 E+ 0 56 E+ 0 521.496555.551676.736777.160377.5839114.6829119.2300122.8530126.4190138.6244148.8500155.6154Figure A.2. N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline  (P1). 13C NMR (100 MHz, CDCl3, 298K).10201234567891 01 11 21 3f1  (ppm)- 5 0 0 005 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 03 5 0 0 04 0 0 0 04 5 0 0 05 0 0 0 05 5 0 0 06 0 0 0 06 5 0 0 07 0 0 0 07 5 0 0 08 0 0 0 08 5 0 0 09 0 0 0 06.016.001.874.003.772.27193.79546.65436.79926.82896.99377.02217.2598Figure A.3. 4-Bromo-N,N-bis(4-methoxyphenyl)3,5-dimethylaniline (P2). 1H NMR (300 MHz, CDCl3, 298K). 103- 1 002 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)- 2 E+ 0 502 E+ 0 54 E+ 0 56 E+ 0 58 E+ 0 51 E+ 0 61 E+ 0 61 E+ 0 62 E+ 0 62 E+ 0 62 E+ 0 62 E+ 0 62 E+ 0 63 E+ 0 63 E+ 0 63 E+ 0 63 E+ 0 63 E+ 0 64 E+ 0 64 E+ 0 623.998924.014724.062824.111924.127755.606676.843077.160377.363777.4776114.8100118.5489120.9179126.5199138.6930147.4393155.8893Figure A.4. 4-Bromo-N,N-bis(4-methoxyphenyl)3,5-dimethylaniline (P2). 13C NMR (100 MHz, CDCl3, 298K).10401234567891 01 11 21 3f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 50.941.090.990.961.060.952.850.951.000.071.577.167.177.267.377.387.397.397.407.407.507.858.588.608.658.658.738.74Figure A.5. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine  (P6). 1H NMR (300 MHz, CDCl3, 298K).1057 . 07 . 27 . 47 . 67 . 88 . 08 . 28 . 48 . 68 . 8f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 50.941.090.990.961.060.952.850.951.007.167.177.267.377.397.407.507.517.857.867.887.897.917.927.947.947.978.588.608.658.738.74Figure A.6. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine  (P6). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region.10602 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 576.737177.160577.5837115.0483118.1231122.7422122.8956125.3518127.1530128.9664137.2464149.3745154.3244155.2695157.3372Figure A.7. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine  (P6). 13C NMR (100 MHz, CDCl3, 298K).1071 1 51 2 01 2 51 3 01 3 51 4 01 4 51 5 01 5 51 6 0f1  (ppm)05 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 0115.0483116.2938118.1231121.5708122.7422122.8448124.5505126.4411127.1530128.9664131.5465131.6474132.0898132.5320132.9753137.2464141.2258142.5644143.1302149.3745154.3244155.2695157.3372Figure A.8. 6-(3,5-bis(trifluoromethyl)phenyl)-4-(5-bromothiophen-2-yl)-2,2’-bipyridine  (P6). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region.10801234567891 01 11 21 3f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 56.006.032.005.003.981.141.192.141.121.131.102.191.021.071.072.10122.16423.81566.66816.86967.09667.13817.34247.36737.48517.68777.95278.62368.62878.65538.68188.71738.72028.72298.72558.73328.73618.73888.7414Figure A.9. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L1). 1H NMR (300 MHz, CDCl3, 298K).1096 . 66 . 87 . 07 . 27 . 47 . 67 . 88 . 08 . 28 . 48 . 68 . 89 . 0f1  (ppm)- 5 0 0 005 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 03 5 0 0 04 0 0 0 04 5 0 0 05 0 0 0 05 5 0 0 06 0 0 0 02.005.003.981.141.192.141.121.131.102.191.021.071.076.66816.83526.84696.85436.87697.08517.10417.12657.26017.32647.44127.48517.53737.68777.69987.83867.86467.89027.94758.18278.20598.21098.62368.62878.65538.68188.71738.72028.72298.72558.73328.7388Figure A.10. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L1). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region.11002 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 521.228255.631376.739077.162377.5857114.8611118.8243127.1279139.0001140.9124156.1173Figure A.11. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L1). 13C NMR (100 MHz, CDCl3, 298K).1111 1 61 2 01 2 41 2 81 3 21 3 61 4 01 4 41 4 81 5 21 5 6f1  (ppm)- 2 0 0 0- 1 0 0 001 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 07 0 0 08 0 0 09 0 0 01 0 0 0 01 1 0 0 01 2 0 0 01 3 0 0 01 4 0 0 01 5 0 0 01 6 0 0 01 7 0 0 01 8 0 0 01 9 0 0 02 0 0 0 02 1 0 0 02 2 0 0 02 3 0 0 0114.8611115.6551116.6560118.8243121.6695124.0034125.2566127.1279128.4256128.8888129.2733137.0636139.0001140.9124143.6382144.3131148.7844149.1635156.1173156.3804156.4877157.4219Figure A.12. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L1). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region.11201234567891 01 11 21 3f1  (ppm)05 0 0 0 01 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 54 E+ 0 56.156.132.015.104.071.051.001.991.041.011.021.001.030.951.002.10563.81646.67316.85626.88557.09767.12747.34457.36947.62317.70728.34968.37528.46148.62668.65328.67178.67678.72528.72788.73068.73318.74118.74378.7465Figure A.13. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L2). 1H NMR (300 MHz, CDCl3, 298K).1136 . 66 . 87 . 07 . 27 . 47 . 67 . 88 . 08 . 28 . 48 . 68 . 89 . 0f1  (ppm)05 0 0 0 01 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 54 E+ 0 52.015.104.071.051.001.991.041.011.021.001.030.951.006.67316.83746.84896.85626.87897.08627.10497.12747.26017.34457.36437.38557.62317.64887.67457.70727.71937.85997.86587.88597.89187.91157.95758.34968.37528.46148.62668.65328.67178.67678.72528.72788.73068.7331Figure A.14. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L2). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region.11402 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 0f1  (ppm)- 2 0 0 0 002 0 0 0 04 0 0 0 06 0 0 0 08 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 53 E+ 0 53 E+ 0 521.217155.618576.842277.159877.4773114.8505118.8079123.9803124.0917125.7547125.8694128.5100130.8459140.8747155.8005156.0060156.1128156.7885Figure A.15. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L2). 13C NMR (100 MHz, CDCl3, 298K).1151 1 41 1 81 2 21 2 61 3 01 3 41 3 81 4 21 4 61 5 01 5 41 5 8f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 5114.8505116.2926118.8079121.6177123.0298124.0561125.0966127.1223128.5100129.3459130.3609130.8459131.1674131.4887137.1346138.9579140.2682140.8747141.1572143.9621144.6839148.8295149.2573155.8005156.0060156.1128156.7885Figure A.16. N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(5-(6-(3-(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)aniline  (L2). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region.11601234567891 01 11 21 3f1  (ppm)- 5 0 0 0 005 0 0 0 01 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 54 E+ 0 54 E+ 0 54 E+ 0 55 E+ 0 56 E+ 0 56 E+ 0 511.3111.423.807.541.837.532.042.021.943.651.004.523.662.10703.81775.29856.67376.87897.09587.26007.39297.96718.59868.62868.72618.73108.73828.74118.74348.75168.75428.7570Figure A.17. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3).1H NMR (300 MHz, CDCl3, 298K).1176 . 56 . 76 . 97 . 17 . 37 . 57 . 77 . 98 . 18 . 38 . 58 . 78 . 9f1  (ppm)05 0 0 0 01 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 53 E+ 0 54 E+ 0 53.807.541.837.532.042.021.943.651.004.523.666.67376.83736.85636.87896.90207.08447.10337.12577.26007.36797.38407.39297.40897.73197.74417.88567.89167.91167.91747.93737.94327.96718.59868.62868.72618.73108.73828.74118.7542Figure A.18. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region.11802 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 521.209629.843955.624276.737177.160577.5839114.8652116.6331117.0142118.1696118.8460121.6036121.7845122.6788124.3960124.9655125.3987126.3729127.1256128.6126129.0145131.5874132.0288132.4707132.9121137.2393138.9276156.1379Figure A.19. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 13C NMR (100 MHz, CDCl3, 298K).1191 1 61 2 01 2 41 2 81 3 21 3 61 4 01 4 41 4 81 5 21 5 6f1  (ppm)- 5 0 0 005 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 03 5 0 0 04 0 0 0 04 5 0 0 05 0 0 0 05 5 0 0 06 0 0 0 06 5 0 0 07 0 0 0 07 5 0 0 08 0 0 0 08 5 0 0 0114.8652116.6331118.1696118.8460121.6036121.7845122.6788124.3960124.9655127.1256128.6126129.0145131.5874132.0288132.4707132.9121137.2393138.9276140.7571140.8745144.3281145.1232148.9031149.3375154.1453155.6307156.1379157.0989Figure A.20. 4-(5-(6-(3,5-bis(trifluoromethyl)phenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline (L3). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region.12001234567891 01 11 21 3f1  (ppm)- 2 0 0 0 0- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 51 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 52 E+ 0 55.966.233.172.075.161.114.131.341.211.081.091.011.111.011.961.000.07141.23601.25981.28361.43301.58091.88112.04542.09613.81433.94184.11084.13466.66296.87407.02397.10047.33257.35727.41827.70147.93008.63448.63818.64548.67238.71958.72218.73538.7379Figure A.21. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline (L4). 1H NMR (300 MHz, CDCl3, 298K).1216 . 66 . 87 . 07 . 27 . 47 . 67 . 88 . 08 . 28 . 48 . 68 . 8f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 52.075.161.114.131.341.211.081.091.011.111.011.961.006.66296.84406.85136.86706.87406.99877.03247.09297.11567.26027.33257.34907.35727.37347.47127.68937.70147.72657.75347.77967.78747.84197.84767.86797.87337.93008.63448.63818.64548.67238.71958.72218.73538.7379Figure A.22. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline (L4). 1H NMR (300 MHz, CDCl3, 298K); expansion of aromatic region.12202 04 06 08 01 0 01 2 01 4 01 6 01 8 02 0 02 2 0f1  (ppm)05 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 021.227031.075555.634076.736677.160177.5833100.1240112.9368114.8592116.8072119.6312127.1261137.1023141.0385144.3527156.1123156.3018157.1719160.2212Figure A.23. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline (L4). 13C NMR (100 MHz, CDCl3, 298K).1231 0 01 0 51 1 01 1 51 2 01 2 51 3 01 3 51 4 01 4 51 5 01 5 51 6 0f1  (ppm)- 1 0 0 001 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 07 0 0 08 0 0 09 0 0 01 0 0 0 01 1 0 0 01 2 0 0 01 3 0 0 01 4 0 0 01 5 0 0 01 6 0 0 01 7 0 0 01 8 0 0 0100.1240112.9368114.7617115.8195118.8254121.6832124.0308125.2443125.8529127.1261128.4397129.8884137.1023138.9948140.9127143.6477144.3527148.7839149.1264156.1123156.3018157.1719160.2212Figure A.24. N,N-bis(4-methoxyphenyl)-[2,2’-bipyridin]-4-yl)thiophen-2-yl)-3,5-dimethylaniline (L4). 13C NMR (100 MHz, CDCl3, 298K); expansion of aromatic region.1241 . 52 . 02 . 53 . 03 . 54 . 04 . 55 . 05 . 56 . 06 . 57 . 07 . 58 . 08 . 59 . 09 . 5f1  (ppm)- 1 0 0 001 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 07 0 0 08 0 0 09 0 0 01 0 0 0 01 1 0 0 01 2 0 0 05.712.941.001.361.301.172.563.331.001.301.342.141.301.101.661.411.362.15992.69903.30463.30963.31453.80964.86185.56705.59166.68466.93027.45087.59797.89747.96978.52688.74059.00989.2314Figure A.25. [Ru(L1)(L5)]NO3 (2). 1H NMR (300 MHz, MeOD, 298K). 1255 . 66 . 06 . 46 . 87 . 27 . 68 . 08 . 48 . 89 . 2f1  (ppm)05 0 01 0 0 01 5 0 02 0 0 02 5 0 01.001.361.301.172.563.331.001.301.342.141.301.101.661.411.365.56705.59166.68466.93027.06207.45087.46867.58297.64947.89747.94568.13758.14978.52688.74058.76738.79559.00989.2314Figure A.26. [Ru(L1)(L5)]NO3 (2). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region. 12601234567891 01 11 21 3f1  (ppm)- 2 0 0 0- 1 0 0 001 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 07 0 0 08 0 0 09 0 0 01 0 0 0 01 1 0 0 01 2 0 0 01 3 0 0 01 4 0 0 01 5 0 0 01 6 0 0 01 7 0 0 01 8 0 0 01 9 0 0 02 0 0 0 02 1 0 0 02 2 0 0 08.936.381.602.001.333.924.581.491.214.311.852.671.661.371.572.692.582.70093.80855.86715.89346.68686.89837.12477.55868.19968.66358.75198.77938.83198.83568.99559.2287Figure A.27. [Ru(L2)(L5)]NO3 (4). 1H NMR (300 MHz, MeOD, 298K).1276 . 06 . 57 . 07 . 58 . 08 . 59 . 09 . 5f1  (ppm)- 1 0 0 001 0 0 02 0 0 03 0 0 04 0 0 05 0 0 06 0 0 07 0 0 08 0 0 09 0 0 01 0 0 0 01 1 0 0 01 2 0 0 01.602.001.333.924.581.491.214.311.852.671.661.371.572.692.585.86715.89346.68686.72736.73076.75376.75776.89837.05097.09217.14597.49507.50867.55867.58127.59707.91297.91597.93897.94398.18688.19968.20808.66358.75198.77938.83568.99559.2287Figure A.28. [Ru(L2)(L5)]NO3 (4). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region.12801234567891 01 11 21 3f1  (ppm)- 1 0 0 0 001 0 0 0 02 0 0 0 03 0 0 0 04 0 0 0 05 0 0 0 06 0 0 0 07 0 0 0 08 0 0 0 09 0 0 0 01 E+ 0 51 E+ 0 51 E+ 0 528.429.745.4510.072.403.532.486.5910.082.303.144.592.751.002.132.111.841.813.943.640.84870.86950.89080.91821.31582.15702.81653.29953.80804.84986.06126.08806.68426.99497.63617.72988.57288.57578.70018.72808.76439.03069.2656Figure A.29. [Ru(L4)(L5)]NO3 (8). 1H NMR (300 MHz, MeOD, 298K).1295 . 86 . 06 . 26 . 46 . 66 . 87 . 07 . 27 . 47 . 67 . 88 . 08 . 28 . 48 . 68 . 89 . 09 . 29 . 4f1  (ppm)- 5 0 0 005 0 0 01 0 0 0 01 5 0 0 02 0 0 0 02 5 0 0 03 0 0 0 03 5 0 0 04 0 0 0 04 5 0 0 05 0 0 0 05 5 0 0 06 0 0 0 06 5 0 0 07 0 0 0 02.403.532.486.5910.082.303.144.592.751.002.132.111.841.813.943.646.06126.08806.68426.79396.82026.84686.89716.92706.99497.05807.08807.63617.65587.69477.72057.86488.07178.14448.15668.57288.57578.70018.72808.76439.03069.2656Figure A.30. [Ru(L4)(L5)]NO3 (8). 1H NMR (300 MHz, MeOD, 298K); expansion of aromatic region.130  Figure A.31. UV-vis absorption spectra of ligand L1 in MeOH where R1, R2 = −H.     Figure A.32. UV-vis absorption spectra of ligand L2 in MeOH where R1 = −CF3, R2 = −H. 131   Figure A.33. UV-vis absorption spectra of ligand L3 in MeOH where R1 = −CF3, R2 = −CF3.   Figure A.34. UV-vis absorption spectra of ligand L4 in MeOH where R1 = −H, R2 = −OMe. 132  Figure A.35. UV-vis absorption spectra of ligands in MeOH demonstrating minor optical changes when R1, R2 = −H (L1), R1 = −CF3, R2 = −H (L2), R1 = −CF3, R2 = −CF3 (L3) and R1 = −H, R2 = −OMe (L4).   Figure A.36. Cyclic voltammogram for ligand L1 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s. 133 Figure A.37. Cyclic voltammogram for ligand L2 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.   Figure A.38. Cyclic voltammogram for ligand L3 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.  134 Figure A.39. Cyclic voltammogram for ligand L4 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.   Figure A.40. Cyclic voltammogram for ligand 2 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.  135  Figure A.41. Cyclic voltammogram for ligand 4 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.  Figure A.42. Cyclic voltammogram for ligand 8 in CH2Cl2 at ambient temperatures. Data collected using 0.1 M NBu4BF4/ CH2Cl2 solutions at a scan rate 100 mV/s.  136APPENDIX B: GAUSSIAN DATA  Table B.1. Optimized Cartesian Coordinates for (2).  Atom Ru         X -4.622058      Y -0.028504   Z -0.013999 N -2.603173 -0.222942 0.399118 N -3.626073 -0.154501 -2.022738 N -4.813538 2.062339 -0.110545 N -6.56204 0.158792 -0.333872 N -5.220428 -2.043743 -0.050489 C -4.654161 0.000712 2.042828 C -5.751118 0.120437 2.910684 H -6.755025 0.218956 2.503104 C -5.589081 0.115477 4.30009 H -6.459574 0.209857 4.945627 C -4.315049 -0.011314 4.864869 H -4.189371 -0.016493 5.943868 C -3.20484 -0.131519 4.032837 H -2.217778 -0.231372 4.476807 C -3.36141 -0.125303 2.636085 C -2.22759 -0.246811 1.706753 C -0.875711 -0.363865 2.035628 H -0.573116 -0.349472 3.075311 C 0.097167 -0.472197 1.027532 C -0.336124 -0.447066 -0.312266 H 0.383314 -0.547804 -1.115397 C -1.692546 -0.31697 -0.597549 C -2.271742 -0.276751 -1.961039 C -1.502997 -0.355831 -3.126908 H -0.425326 -0.449774 -3.069144 C -2.131981 -0.312632 -4.368467 H -1.544546 -0.373667 -5.278837 C -3.520026 -0.190571 -4.421305 H -4.051879 -0.153726 -5.365544 C -4.225369 -0.114474 -3.223373 H -5.306077 -0.018314 -3.214208 C -3.844387 2.989083 0.015765 H -2.84557 2.609734 0.195356 C -4.088279 4.353013 -0.074418 H -3.272761 5.056671 0.035763 C -5.398133 4.787732 -0.307735 C -6.408492 3.836294 -0.438867                    137Atom H         X -7.423407       Y 4.168424   Z -0.619638 C -6.102279 2.479923 -0.335261 C -7.099519 1.405727 -0.4562 C -8.466201 1.561456 -0.672633 H -8.907073 2.545123 -0.768813 C -9.275541 0.421699 -0.763945 C -8.702942 -0.850097 -0.637332 H -9.342322 -1.7212 -0.709947 C -7.333813 -0.962932 -0.420791 C -6.56589 -2.207778 -0.263404 C -7.136183 -3.480839 -0.324717 H -8.198945 -3.596808 -0.493536 C -6.327952 -4.606248 -0.166881 C -4.957632 -4.427249 0.052167 H -4.306021 -5.283193 0.180174 C -4.449244 -3.138004 0.104217 H -3.395171 -2.954866 0.274174 C 1.512577 -0.606337 1.37315 C 2.061781 -1.064618 2.552001 S 2.786838 -0.169128 0.250032 C 3.483127 -1.071713 2.554563 H 1.465305 -1.415956 3.386866 C 4.046296 -0.619981 1.383848 H 4.079389 -1.409876 3.395228 C 5.479267 -0.465051 1.035233 C 6.133619 -1.429667 0.235259 C 6.204359 0.654126 1.507092 C 7.483034 -1.264116 -0.081156 C 7.553876 0.789219 1.181168 C 8.216361 -0.157722 0.380467 H 7.972593 -2.006545 -0.702438 H 8.103077 1.645447 1.558176 N 9.578105 -0.001718 0.053791 C 10.161794 1.296596 -0.058139 C 11.382577 1.583184 0.577209 C 9.55007 2.303827 -0.813521 C 11.969432 2.836131 0.454556 H 11.871544 0.814083 1.167268 C 10.121705 3.573991 -0.923533 H 8.611616 2.098207 -1.319192 C 11.341813 3.8466 -0.291696 H 12.912901 3.058042 0.944176                    138Atom H        X 9.615682       Y 4.329327  Z -1.513473 C 10.4007 -1.137142 -0.217318 C 11.184198 -1.189892 -1.375231 C 10.462625 -2.214493 0.684231 C 12.018019 -2.280383 -1.636311 H 11.148684 -0.366308 -2.081934 C 11.27205 -3.312206 0.422242 H 9.86934 -2.187281 1.593146 C 12.061581 -3.354499 -0.738801 H 12.613551 -2.282829 -2.541744 H 11.319993 -4.145418 1.116937 C 5.54696 1.708327 2.371137 H 4.65692 2.127064 1.886741 H 5.21834 1.297073 3.332603 H 6.239513 2.530027 2.575611 C 5.396989 -2.640656 -0.294521 H 4.864555 -3.167411 0.505332 H 4.646106 -2.361633 -1.04374 H 6.0907 -3.343841 -0.764506 O 11.993166 5.045686 -0.339544 O 12.829908 -4.471735 -0.897618 C 11.395166 6.106758 -1.077784 H 12.06806 6.959405 -0.974566 H 11.294237 5.850014 -2.13954 H 10.409793 6.369812 -0.673687 C 13.648808 -4.564913 -2.059462 H 14.170305 -5.520127 -1.981965 H 13.046594 -4.552588 -2.976301 H 14.383543 -3.751269 -2.098022 C -10.744072 0.507439 -0.99421 O -11.477262 -0.460469 -1.07994 O -11.181211 1.777127 -1.099413 H -12.145904 1.742528 -1.247482 C -5.765936 6.230606 -0.422077 O -6.895283 6.627191 -0.637377 O -4.709338 7.04643 -0.259593 H -5.030613 7.964996 -0.345147 C -6.870599 -5.996286 -0.222313 O -6.187997 -6.993844 -0.091388 O -8.199044 -6.026804 -0.433274 H -8.472165 -6.964429 -0.454391   139Table B.2. Optimized Cartesian Coordinates for (4).  Atom Ru         X -4.382522     Y -0.01657  Z -0.496281 N -2.380523 -0.21153 -0.020195 N -3.319172 -0.046578 -2.472153 N -4.587712 2.077788 -0.524533 N -6.31207 0.170649 -0.890801 N -4.965797 -2.034844 -0.634656 C -4.491679 -0.06914 1.551344 C -5.620588 0.001721 2.386395 C -5.511981 -0.056649 3.774849 H -6.403261 -0.005616 4.394093 C -4.252941 -0.190403 4.376336 C -3.109708 -0.263751 3.583253 H -2.1422 -0.373107 4.061799 C -3.219545 -0.205712 2.187228 C -2.049135 -0.284808 1.296447 C -0.711084 -0.407876 1.670377 H -0.446832 -0.434681 2.720152 C 0.29813 -0.471681 0.693361 C -0.089373 -0.395251 -0.658365 H 0.658075 -0.460628 -1.439201 C -1.435259 -0.259348 -0.987418 C -1.966534 -0.161849 -2.367507 C -1.156013 -0.179029 -3.50708 H -0.080046 -0.265556 -3.415446 C -1.740657 -0.080619 -4.767195 H -1.120489 -0.093263 -5.657546 C -3.126661 0.034848 -4.864253 H -3.624708 0.114392 -5.824149 C -3.875164 0.048399 -3.690263 H -4.956079 0.13879 -3.71596 C -3.632247 3.005132 -0.32523 H -2.638867 2.626135 -0.11717 C -3.883531 4.370054 -0.377652 H -3.079035 5.074914 -0.209556 C -5.18614 4.803383 -0.648665 C -6.182692 3.850469 -0.85459 H -7.192057 4.182169 -1.06499 C -5.86914 2.493609 -0.78818 C -6.851648 1.417558 -0.992308 C -8.208404 1.573547 -1.265               140Atom H         X -8.651824    Y 2.557303  Z -1.346282 C -9.003842 0.433246 -1.43392 C -8.428625 -0.838879 -1.327863 H -9.057667 -1.710225 -1.461634 C -7.069552 -0.951264 -1.053797 C -6.300203 -2.197301 -0.907755 C -6.860462 -3.469863 -1.033777 H -7.914698 -3.584897 -1.249781 C -6.053009 -4.596364 -0.879208 C -4.694121 -4.41907 -0.598839 H -4.043397 -5.275828 -0.471933 C -4.195281 -3.129781 -0.484622 H -3.149934 -2.948418 -0.265825 C 1.701257 -0.611517 1.081611 C 2.213813 -1.087434 2.270259 S 3.009877 -0.157892 0.005428 C 3.634232 -1.094617 2.317053 H 1.592547 -1.45039 3.08169 C 4.233159 -0.625623 1.171039 H 4.204067 -1.444635 3.171057 C 5.675735 -0.468184 0.86525 C 6.356824 -1.439107 0.095938 C 6.381318 0.660285 1.344071 C 7.713554 -1.269805 -0.18506 C 7.738594 0.799119 1.05386 C 8.427666 -0.153307 0.282559 H 8.223854 -2.016469 -0.784119 H 8.272843 1.662642 1.435668 N 9.796581 0.007174 -0.00997 C 10.375064 1.307484 -0.125413 C 11.579622 1.609322 0.533401 C 9.775019 2.301298 -0.907509 C 12.162044 2.864051 0.407815 H 12.059493 0.850663 1.144078 C 10.341868 3.573292 -1.021003 H 8.849494 2.083649 -1.431613 C 11.545807 3.861173 -0.365403 H 13.092931 3.09776 0.915679 H 9.845095 4.318004 -1.631954 C 10.63175 -1.126599 -0.248114 C 11.43992 -1.189955 -1.388384 C 10.680516 -2.191315 0.669033               141Atom C        X 12.285719    Y -2.278545  Z -1.61684 H 11.41426 -0.376167 -2.106763 C 11.501961 -3.287304 0.439295 H 10.067619 -2.155443 1.564536 C 12.31639 -3.340156 -0.704016 H 12.900343 -2.289713 -2.509314 H 11.539964 -4.110906 1.145952 C 5.693875 1.719299 2.178164 H 4.821751 2.135339 1.660011 H 5.331019 1.312693 3.129276 H 6.378578 2.542271 2.402818 C 5.640448 -2.659724 -0.439258 H 5.106606 -3.19188 0.356174 H 4.893444 -2.390559 -1.195832 H 6.347295 -3.355222 -0.900949 O 12.191321 5.063398 -0.413954 O 13.094341 -4.454752 -0.831211 C 11.603615 6.111911 -1.177957 H 12.269332 6.969662 -1.070564 H 11.527291 5.84186 -2.238466 H 10.608223 6.374113 -0.798599 C 13.938559 -4.558704 -1.973861 H 14.462734 -5.510249 -1.872867 H 13.356233 -4.561055 -2.903543 H 14.670166 -3.741995 -2.007069 C -10.462024 0.519031 -1.726927 O -11.182765 -0.449689 -1.879218 O -10.902212 1.789028 -1.806619 H -11.859157 1.75575 -1.998903 C -5.561289 6.247343 -0.727364 O -6.686598 6.642319 -0.964666 O -4.516266 7.063717 -0.506445 H -4.840624 7.982831 -0.572683 C -6.585669 -5.986613 -1.00115 O -5.902954 -6.984522 -0.875243 O -7.904183 -6.015141 -1.265879 H -8.171883 -6.952469 -1.329312 C -4.14588 -0.197313 5.871224 F -5.124097 -0.937764 6.447755 F -4.259448 1.050576 6.397485 F -2.963038 -0.691463 6.304766 H -6.611229 0.10147 1.950024  142Table B.3. Optimized Cartesian Coordinates for (8).  Atom Ru         X -4.420896    Y -0.049731   Z -0.061454 N -2.406232 -0.266358 0.340259 N -3.414112 0.284152 -2.02471 N -4.679361 2.006591 0.291508 N -6.341567 0.167014 -0.47401 N -4.953625 -2.023482 -0.550149 C -4.468126 -0.46607 1.972502 C -5.571292 -0.573398 2.848729 C -5.400917 -0.862305 4.208569 H -6.255235 -0.943111 4.87143 C -4.115166 -1.05209 4.732363 C -3.00453 -0.954445 3.908544 H -2.012878 -1.104473 4.324646 C -3.18005 -0.663131 2.540306 C -2.038452 -0.546125 1.618529 C -0.685138 -0.680281 1.935328 H -0.39402 -0.873583 2.959722 C 0.299304 -0.542967 0.941564 C -0.127988 -0.259753 -0.370461 H 0.598295 -0.160092 -1.167534 C -1.486086 -0.122289 -0.641824 C -2.057089 0.179768 -1.974572 C -1.280203 0.352663 -3.124806 H -0.201415 0.266932 -3.076615 C -1.901578 0.63616 -4.33809 H -1.307362 0.771492 -5.235951 C -3.291297 0.74283 -4.378853 H -3.81797 0.962705 -5.300854 C -4.005776 0.559167 -3.19847 H -5.088106 0.632365 -3.182276 C -3.759907 2.896712 0.71042 H -2.766912 2.503052 0.890847 C -4.045801 4.241566 0.906477 H -3.268807 4.915935 1.243917 C -5.346637 4.694558 0.659608 C -6.306794 3.779172 0.230447 H -7.315566 4.12588 0.042247 C -5.960125 2.440563 0.053706 C -6.904787 1.402341 -0.385568 C -8.251136 1.582983 -0.691717                143Atom H         X -8.711932    Y 2.559919   Z -0.626404 C -9.012897 0.47631 -1.088346 C -8.411601 -0.785497 -1.176315 H -9.012362 -1.631461 -1.486867 C -7.063614 -0.919705 -0.862894 C -6.272819 -2.15905 -0.900768 C -6.797581 -3.399594 -1.267473 H -7.839692 -3.491685 -1.544879 C -5.970641 -4.522879 -1.275082 C -4.62779 -4.373728 -0.911629 H -3.962339 -5.228588 -0.907126 C -4.164013 -3.115386 -0.557845 H -3.131895 -2.956395 -0.269613 C 1.717299 -0.689089 1.271575 C 2.278606 -1.246628 2.401503 S 2.983113 -0.124932 0.194841 C 3.699326 -1.221413 2.406745 H 1.693697 -1.680777 3.204717 C 4.251648 -0.643905 1.287407 H 4.302882 -1.618258 3.215925 C 5.682539 -0.448053 0.949716 C 6.435155 -1.516453 0.40974 C 6.307256 0.800634 1.1743 C 7.783346 -1.324698 0.103903 C 7.659426 0.959199 0.869115 C 8.419099 -0.091833 0.327867 H 8.34912 -2.145853 -0.323731 H 8.135799 1.914346 1.064224 N 9.783585 0.088343 0.021435 C 10.269371 1.361049 -0.40627 C 11.409507 1.926713 0.190322 C 9.637062 2.064511 -1.437974 C 11.90002 3.153347 -0.238975 H 11.912558 1.395541 0.992608 C 10.110301 3.309049 -1.861176 H 8.760621 1.638699 -1.916986 C 11.252367 3.859687 -1.265561 H 12.781581 3.590624 0.220113 H 9.591439 3.825095 -2.66062 C 10.702718 -0.999827 0.101414 C 11.606847 -1.249506 -0.937227 C 10.741354 -1.829419 1.236727                144Atom C        X 12.53541    Y -2.290665  Z -0.854732 H 11.591623 -0.619956 -1.821625 C 11.645207 -2.880659 1.316551 H 10.055406 -1.646228 2.057968 C 12.555326 -3.119382 0.273764 H 13.222641 -2.448833 -1.677793 H 11.67463 -3.521962 2.192355 C 5.543181 1.966183 1.763318 H 4.797875 2.356302 1.059224 H 5.000137 1.674385 2.669039 H 6.22031 2.786503 2.018699 C 5.802476 -2.864548 0.141675 H 5.481667 -3.350179 1.070732 H 4.911685 -2.773665 -0.490753 H 6.508403 -3.532749 -0.360157 O 11.806763 5.059799 -1.606902 O 13.410141 -4.168911 0.455526 C 11.191105 5.812964 -2.647288 H 11.785566 6.722004 -2.750576 H 11.197759 5.264115 -3.597058 H 10.158504 6.080565 -2.391188 C 14.356585 -4.449101 -0.571116 H 14.929912 -5.30965 -0.222941 H 13.860213 -4.701224 -1.516377 H 15.034319 -3.601845 -0.733189 C -10.457986 0.58804 -1.428582 O -11.150074 -0.350499 -1.778087 O -10.926197 1.845499 -1.308441 H -11.873047 1.82794 -1.546988 C -5.757453 6.119174 0.836495 O -6.882371 6.531344 0.626833 O -4.745464 6.900433 1.253806 H -5.092979 7.809003 1.343587 C -6.465025 -5.878731 -1.657975 O -5.765693 -6.87321 -1.676877 O -7.771207 -5.882407 -1.981128 H -8.013542 -6.798833 -2.216831 H -3.996357 -1.276305 5.788682 O -6.810675 -0.376491 2.28836 C -7.958036 -0.468587 3.122415 H -8.057622 -1.467813 3.565557 H -7.935962 0.279388 3.925387 H -8.814676 -0.275357 2.474463 145Table B.4. Potential Energy Scan for (2) About the Dihedral Angle Between Atoms S58, C61, C63, and C65.  Dihedral angle (°) -90.5 Energy (kJ/mol) 0.183785 -80.5 0.551355 -70.5 0.73514 -60.5 1.73283 -50.5 3.78072 -40.5 7.40391 -30.5 12.6024 -20.5 18.95611 -10.5 25.62488 -0.5 30.56082 9.5 24.83723 19.5 18.19472 29.5 12.20857 39.5 7.535185 49.5 4.279565 59.5 2.31044 69.5 1.286495 79.5 0.99769 89.5 1.10271 99.5 1.26024 109.5 1.31275 119.5 2.25793 129.5 4.14829 139.5 7.56144 149.5 12.73368 159.5 18.9036 169.5 25.57237 179.5 30.16699 189.5 25.09978 199.5 17.93217 209.5 11.44718 219.5 6.432475 229.5 3.071835 239.5 1.31275 249.5 0.393825 259.5 0  146APPENDIX C: ATTEMPTED SYNTHESIS  In this work a series of ruthenium(II) bis-tridentate complexes of the formula [Ru(II)(TPA-2,5-thiophene-pbpy)(tctpy)]were investigated. A synthetic approach similar to that reported in literature was adopted.37,58 Not all of the complexes that were sought out were successfully synthesized as well as precursor P3 was synthesized in low yield. A description and explanation of the synthesis and synthetic outcomes are provided below.     Figure C.1. Attempted lithiation of P2 using trimethylborate.   (4-(bis(4-methoxyphenyl)amino)-2,6-dimethylphenyl)boronic acid. Attempt (1) – butyllithium method (Figure C.1.). A solution of P2 (0.253 g, 0.614 mmol) in anhydrous THF (3 mL) was cooled to -78°C under nitrogen. A solution of n-butyllithium in hexane (0.58 mL, 1.6 M, 0.920 mmol) was added dropwise over 10 min via syringe. The solution was allowed to stir for 30 min, then the reaction was warmed to 0°C and then brought back down to -78°C whereupon trimethylborate (0.14 mL, 1.23 mmol) was added in one portion and stirred for 30 min at -78°C. The reaction was allowed to warm to room temperature and was stirred overnight. The reaction was quenched and hydrolyzed with 2M HCl solution (20 mL) and was stirred for one hour at room temperature. The solution was diluted with diethyl ether and washed with 3 × 30 mL H2O. The organic layer was 1)THF, -78°C2) nBuLi, 30 min → 0°C3)trimethylborate, -78°C4) 2M HClNOMeMeOBrNOMeMeOBHOOHP2 P3147separated, dried over MgSO4, filtered and evaporated to give a clear oil. Spectroscopic examination (NMR) of the yellow liquid indicated that only the starting material had been recovered.  Figure C.2. Attempted lithiation of P2 using triisopropylborate.   Attempt (1a) – butyllithium method (Figure C.2.). To a solution of P2 (0.050 g, 0.150 mmol) in anhydrous THF, n-butyllithium (0.14 mL, 1.6 M in hexane, 0.225 mmol) was added dropwise at room temperature and stirred for 1 h. Triisopropylborate (0.05 mL, 0.225 mmol) was added dropwise at room temperature over 10 min and the solution was stirred for 1 h. 2M HCl was added until the reaction was between pH 5-6 and the solution was stirred until the reaction remained clear for 30 min. The solution was diluted with CH2Cl2 and washed with brine (2× 30 mL). The organic fractions were separated, dried over MgSO4, filtered and evaporated under reduced pressure to give a clear oil. Spectroscopic examination (NMR) of the yellow liquid indicated that only the starting material had been recovered.   Figure C.3. Attempted lithiation of P2 using trimethylborate. 1) nBuLi, rt, 1h2) triisopropylborate, 1hr3) 2M HClNOMeMeOBrNOMeMeOBHOOHP2 P3THF1) Mg, 50°C, 2 h→ -78°C2) trimethylborate, 2 h,-78°C3) 2M HClNOMeMeOBrNOMeMeOBHOOHP2 P3THF148 Attempt (2) – Grignard method (Figure C.3.).  A solution of Mg (0.018 g, 0.728 mmol, activated by grinding with a mortar and pestle and the addition of a small crystal of iodine (0.005 g, 3.94 mmol)) in THF (2 mL) was heated for 2 h under N2 at 50°C. The reaction mixture was cooled to room temperature and a solution of P2 (0.200 g, 0.485 mmol) in THF (2 mL) was added dropwise to the reaction flask and was stirred at room temperature for 2 h, followed by cooling to -78°C. Trimethylborate (0.101 g, 0.970 mmol) was then added slowly and was stirred for 2 h at -78°C. The reaction was allowed to warm to room temperature and stirred overnight. Water (25 mL) was added with stirring until a homogeneous solution was observed. The mixture was evaporated under reduced pressure. The residue was acidified with 2M HCl (50 mL) and the aqueous solution was extracted with 3× 30 mL Et2O. The organic fractions were combined and dried over MgSO4, filtered and the solvent was removed under reduced pressure to yield a clear oil. Spectroscopic examination (NMR) of the clear liquid indicated that only the starting material had been recovered.    Figure C.4. Attempted lithiation of P2 using 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.   N,N-bis(4-methoxyphenyl)-3,5-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline. Attempt (1)- butyllithium method (Figure C.4.). Compound P2 (0.520 g, 1.26 NOMeMeOBrNOMeMeOBOOP2 P31) THF, -78°C2) nBuLi, 30 min →0°C, -78°C3)4) 2M HClBOOO149mmol) was dissolved in anhydrous THF (10 mL) under nitrogen. The mixture was cooled to -78°C and a solution of n-butyllithium in hexane (0.95 mL, 1.6 M, 1.51 mmol) was added dropwise over 10 min. After the reaction mixture had been stirred for an additional 30 min at -78°C, it was allowed to warm to 0°C.  After warming to 0°C the solution is then cooled back down to -78°C where the 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added quickly in one portion and was stirred for 30 min at -78°C. The reaction was then allowed to warm to room temperature and was stirred overnight. The reaction was quenched and hydrolyzed with 2M HCl solution (20 mL) and was stirred for one hour at room temperature. The solution was diluted with diethyl ether and washed with 3 × 30 mL H2O. The organic layer was separated, dried over MgSO4, filtered and evaporated to give a clear oil. Spectroscopic examination (NMR) of the yellow liquid indicated that only the starting material had been recovered.     Figure C.5. Attempted borylation of P2 using a palladium catalyst.   Attempt (2) – palladium method (low yield) (Figure C.5.). Freshly distilled DMSO stored over molecular sieves (15 mL) containing P2 (0.561 g, 1.36 mmol), bis(pinacolato)diboron (0.380 g, 1.50 mmol), bis(dibenzylideneacetone)palladium(0) (0.172 g, 0.299 mmol), 1,1’-bis(diphenylphosphino)ferrocene (0.332 g, 0.598 mmol), and KOAc (0.440 g, 4.08 mmol) were heated at 80°C for 16 h under nitrogen. Monitoring the NOMeMeOBrPd(dba)2/dppfKOAcDMSO80oC. 16 h, N2OBOBOONOMeMeOBOOP2 P3150reaction by TLC revealed the absence of starting material and presence of product and reduced form of the starting material (P1). The reaction was allowed to cool to room temperature and CH2Cl2 (30 mL) was added and washed with 3 × 30 mL H2O. The organic fractions were separated, dried over MgSO4, filtered and the solvent was removed under reduced pressure to give a brown solid. The brown solid was solubilized in CH2Cl2 and preabsorbed onto silica. The product was purified by chromatographic techniques (SiO2: 1:1 Pet. ether/CH2Cl2). The desired fraction was collected and isolated to yield 0.035 g (6%) of a white solid. Characterization of the product; LRMS and 1H NMR resembled the same as P3.    Figure C.6. Attempted lithiation of 6-phenyl-4-(thiophen-2-yl)-2,2’-bipyridine using trimethylborate.   (5-(6-phenyl-[2,2’-bipyridin]-4-yl)thiophen-2-yl)boronic acid. Attempt – butyllithium method (Figure C.6.). A solution of 6-phenyl-4-(thiophen-2-yl)-2,2’-bipyridine (0.200 g, 0.523 mmol) in anhydrous THF (3 mL) was cooled to -78°C under nitrogen. A solution of n-butyllithium in hexane (0.49 mL, 1.6 M, 0.785 mmol) was added dropwise over 10 min via syringe. The solution was allowed to stir for 30 min, then the reaction was warmed to 0°C and then brought back down to -78°C whereupon trimethylborate (0.14 mL, 1.23 mmol) was added in one portion and stirred for 30 min at -78°C. The reaction was allowed to warm to room temperature and was stirred overnight. The reaction was NNSBOHHONNS 1)THF, -78°C2) nBuLi, 30 min → 0°C3)trimethylborate, -78°C4) 2M HCl151quenched and hydrolyzed with 2M HCl solution (20 mL) and was stirred for one hour at room temperature. The solution was diluted with diethyl ether and washed with 3 × 30 mL H2O. The organic layer was separated, dried over MgSO4, filtered and evaporated to give a brown oil. Spectroscopic examination (NMR) of the brown oil indicated that only the starting material had been recovered.      Figure C.7. Attempted cyclometalation of L3.   [Ru(L3)(L5)]NO3 (5). Attempt (1) (Figure C.7.). To a degassed MeOH/H2O/THF solution (5:1:1, v/v/v, 137 mL) containing L3 (0.140 g, 0.196 mmol) were added L5 (0.121 g, 0.196 mmol) and N-ethylmorpholine (0.25 mL). Following a 16 h reflux, AgNO3 (0.125 g, 0.735 mmol) was added to the reaction mixture, and the resulting mixture was then left to reflux for an additional 1.5 h. The mixture was then cooled and the solvent was removed in vacuo. The product was purified by chromatographic techniques (Al2O3: CH2Cl2/MeOH, 9.5:0.5, Rf = 0.53). The desired fraction was collected and isolated to yield a dark red fine solid. Spectroscopic examination (NMR and LRMS) NNRuNNNCO2MeMeO2CCO2MeSNOMeMeOF3CF3CNNSF3CNOMeMeO N NRuClClNClCO2MeMeO2CCO2Me1) n-ethylmorpholine, reflux 16 h2) AgNO3, reflux 1.5 hMeOH/H2O/THF (5:1:1 v/v/v)CF3+1152of the red solid indicated a mixture of the uncyclometalated and cyclometalated products, where the uncyclometalated product is the major product.      Figure C.8. Attempted cyclometalation of L3.   Attempt (2) (Figure C.8.). To a degassed MeOH/H2O solution (5:1:1, v/v/v, 30 mL) containing L5 (0.050g, 0.0813 mmol), AgNO3 (0.052 g, 0.305 mmol) was added and the solution was refluxed for 14 h. The solution was filtered hot and placed back into a roundbottom flask and degassed for 1 h. L3 (0.070 g, 0.0895 mmol) and n-ethylmorpholine (0.5 mL) were added to the solution. The solution was brought to reflux for 16 h. The mixture was cooled and the solvent was removed in vacuo. The product was purified by size-exclusion chromatography (sephadex, 6 g soaked in MeOH overnight). Spectroscopic examination indicated a mixture of starting uncyclometalated and cyclometalated product.  1) AgNO3, reflux 14 h2)n-ethylmorpholine, reflux 16 hMeOH/H2O/THF (5:1:1 v/v/v)NNRuNNNCO2MeMeO2CCO2MeSNOMeMeOF3CF3CNNSF3CNOMeMeO N NRuClClNClCO2MeMeO2CCO2MeCF3+1153 Figure C.9. Attempted cyclometalation of P6.  Attempt (3) (Figure C.9.). [Ru(P6)(L5)]NO3. L5 (0.050 g, 0.0813 mmol) and AgNO3 (0.052 g, 0.305 mmol) were suspended in a MeOH/H2O (30 mL, 5:1 v/v) solution and then left at reflux for 2 h. The solution was cooled and P6 (0.047 g, 0.0895 mmol) and n-ethylmorpholine (0.5 mL) were added and left to reflux for 14 h. The hot solution was filtered and the solvent was removed in vacuo. The residue was purified by column chromatography (Al2O3, CH2Cl2/MeOH, 9:1, Rf = 0.58) to yield 0.092 g of a dark black microcrystalline solid. The product was confirmed with LRMS and used without further purification.  Figure C.10. Attempted Suzuki cross-coupling of [Ru(P6)(L5)]NO3 and P3. 1) AgNO3, reflux 14 h2)n-ethylmorpholine, reflux 16 hMeOH/H2O/THF (5:1:1 v/v/v)NNRuNNNCO2MeMeO2CCO2MeSF3CF3CNNSF3CBrNNRuClClNClCO2MeMeO2CCO2MeCF3+1BrNNRuNNNCO2MeMeO2CCO2MeSF3CF3C+1BrK2CO3Pd(PPh3)4DMF70oC 20hNOMeMeOBOONNRuNNNCO2MeMeO2CCO2MeSNOMeMeOF3CF3C+1154Attempt (3a) (Figure C.10.). [Ru(P6)(L5)]NO3 (0.092 g, 0.0887 mmol) and P3 (0.043 g, 0.00887 mmol) were solubilized in anhydrous DMF (14 mL). After the mixture was sparged with N2 for 20 min, K2CO3 (0.120 g, 0.869 mmol) and Pd(PPh3)4 (0.010 g, 0.00887 mmol) were added and left to stir for 20 h at 70°C. The solvent was removed in vacuo, leaving a residue that was dissolved in CH2Cl2. The white precipitate (K2CO3) was removed by filtration, and the solvent was removed in vacuo. The product was purified by size-exclusion chromatography (sephadex, 6 g soaked in MeOH overnight). Spectroscopic examination indicated a mixture of starting material and product.   Butyllithium method. Attempts to convert TPA-Br P2 into the boronic acid or the boronic ester using both trimethylborate and triisopropylborate gave a complete protodeboronation of the substrate leading to the only recovery of P1. The gap existing between the two methyl groups was too narrow to allow a reaction with borate. This result was in accordance with work by Diemer et.al.119 who showed that sterically hindered bromoanisoles, after a methyl-lithium exchange, the reaction with triisopropylborate or trimethylborate became more difficult as the steric hindrance in the vicinity of the boron atom was extreme. As a consequence, protodeboronation occurs, leading to the only recovery of dehalogenated product.   Grignard reagent method. Iodine, an aggressive activator of magnesium, was found to be effective in activating magnesium- as oxidation was observed at the magnesium surface. However, reaction of the subsequent Grignard reagent with trimethylborate was ultimately unsuccessful, and NMR and mass spectroscopy confirmed that only the starting material 4-bromo-N,N-bis(4-methoxyphenyl)-3,5-dimethylaniline was isolated. 155Solely obtaining starting material, it is possible that the Grignard reagent did not form: this is difficult to ascertain, as isolation of the reagent is often not possible owing to its instability, and thus immediate use is preferential. Obtaining solely starting material does point towards the Grignard not forming. Subsequently, a Pd-catalyzed reaction was investigated as an alternative.  Pd-catalyzed method. The use of Pd-catalysts in organic synthesis has been studied extensively, in particular for the formation of C-C bonds. Indeed, in this thesis, and in the literature, a Pd-catalyst was used successfully to form boronic esters. The reaction occurred over 16 h and resulted in the formation of both product P3 and the reduced TPA P1. After isolating the product through column chromatography the yield obtained was 6%. Such a low yield shifted the interest towards other Pd-catalyzed reactions to obtain a higher yield.  To prepare the ligands L1-L4 the synthesis of a boronic acid or boronic ester on the TPA or the pbpy chelate for a Suzuki cross-coupling reaction was the most promising synthetic route. The second alternative consisted in synthesizing the boronic ester obtained through the Miyaura’s procedure from the forgoing brominated TPA (P2). The borylation of P2 was first run by using accurate Miyaura’s experimental conditions (Figure C.11.). A crude NMR analysis of the reaction mixture indicated the presence of three compounds in almost equal proportions: the desired boronic ester P3, the starting brominated TPA P2, and the reduced TPA P1 (Table C.1.). The enhancement of the concentration of bis(pinacolato)diboron limited dehalogenation. Unfortunately, the amount of starting material still remained high. On the contrary, the enhancement of concentration of catalyst bettered the borylation yield but still furthered the reduction of 156P2. Finally, the best result was achieved with 2.2 equivalents of bis(pinacolato)diboron in the presence of 20 mol % of catalyst. These optimized conditions permitted for L1-L4 to be synthesized by Suzuki cross coupling in reasonably high yields.     Figure C.11. Experimental conditions for the Miyaura borylation.   Table C.1. Optimization of the synthesis of P3.   Relative quantity of reagents Products detected in the reaction mixture by NMR (%) Entry Bromo-TPA P2 (equiv.) Bis(pinacolato)diboron (equiv.) PdCl2dppf mol% P3 P2 P1 1 1 1.1 10 18 42 30 2 1 1.2 10 31 39 30 3 1 1.1 15 36 29 35 4 1 2.2 20 46 - 54   Cyclometalation. Reagent P3 could be coupled to the chelating ligand P6 via Suzuki cross-coupling to furnish the TPA-functionalized tridentate ligand in high yield. The seemingly trivial task of binding these ligands to the Ru center, however, was proven to be difficult. In the first attempt to synthesize the methyl ester complex, through the same method as complexes 1, 3 and 7, the reaction yielded a mixture of cyclometalated/uncyclometalated products that were not easily separated by column chromatography.  NOMeMeOBrPd(dppf)Cl2, KOAcDMSO80oC. overnight, N2OBOBOONOMeMeOBOOP2 P3P2NOMeMeOHP1157It has been previously reported that similar complexes C-H activation proceeds via an electrophilic metalation reaction. The high valent Ru(III) precursor and electron-withdrawing methyl-ester groups afford an electrophilic metal center primed for electrophilic metalation. Electrophilic metalations involving substituted aromatic molecules typically show little selectivity between different C-H bonds, and the observed selectivity is usually a consequence of steric factors.59 Having two –CF3 groups ortho to the Ru-C bond that is to form could be too much steric hindrance for the bonds to forms.  With the aforementioned synthetic routes exhausted, a less conventional cross coupling reaction involving bis-tridentate Ru coordination complex was focused on. This approach involved the chelation of pro-ligand P6 to Ru(L5)Cl3 to furnish the brominated precursor [Ru(P6)(L5)]NO3. This product was identified through LRMS. The 1H NMR spectrum proved difficult to identify the product as one of the consequences of this synthesis was partial saponification of the product (i.e., one of the methyl esters could be converted into the corresponding carboxylic acid derivative), thereby giving a messy NMR spectrum due to multiple protonation states of the product.  This product was used without further purification, just as all of the methyl ester complexes (i.e., complexes 1,3, and 7), and in turn was reacted with the Suzuki reagent P3 in anhydrous basic DMF. After the cross-coupling reaction the LRMS revealed no presence of product or ligand (as seen with all acid complexes), indicating a fully saponified product. Acid complexes cannot be purified through column chromatography with silica or alumina. A sephadex column was run on the resulting crude product. The 1H NMR spectrum indicated the presence of a mixture of both starting material and product that could not be separated.      158

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