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UBC Theses and Dissertations

Tuning the electronic properties of coordination complexes with sulfur-bridged ligands Brown, Christopher M.


By altering the oxidation state at the sulfur atom of sulfur-bridged ligands we have shown that photophysical properties of coordination complexes can be changed. A new class of sulfur-bridged dipyridyl ligand has been developed for effective “two-level” tuning of the emission colour of Ir(III) complexes. Tuning can occur via the classical method of altering substituents at the pyridyl ring, and/or through oxidizing the sulfur. Changing the oxidation state of the sulfur atom serves as a switch to alter the emissive state from that of mainly ³LC character (blue-green emission) to one of ³MLCT/³LLCT character (yellow emission), evidenced from photophysical characterization and DFT calculations. The larger bite angle of the sulfur-bridged dipyridyl ligands, in conjunction with additional coordination sites afforded by the oxygen atoms at the sulfur, has led to interesting binding modes when bound to copper(I) in heteroleptic diimine-diphosphine species. On increasing steric constraints about the copper(I) center, bimetallic adducts are isolated, with thermally activated delayed fluorescence the mechanism of photoluminescence. Of the copper(I) species reported in this body of work, one was found to exhibit remarkable thermochromic properties not-before seen in a monometallic copper(I) complex. When isolated as an amorphous powder, Cu-Me-DPSO shows a yellow solid state emission, however when heated to 180 ºC a crystalline powder is formed which shows an orange luminescence. This crystalline powder displays a reversible thermochromic solid state emission, from orange at room temperature to yellow at low temperatures. Using solid state variable temperature excitation and absorption data, this phenomenon is attributed to a change in coordination geometry about the copper atom in the excited-state. With a view to further understanding the impact of sulfur oxidation state on the excitedstate properties of coordination complexes, two new Ru(II)-Re(I) dyads were synthesized, for use as CO₂ photocatalysts. Connected by a sulfur-bridged bisphenanthroline bridge, oxidation state at the sulfur can be changed which could modulate the electron transfer from the photo-excited Ru(II) to the catalytic Re(I) center. The synthesis, characterization and preliminary photocatalytic results are discussed.

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