Design, Synthesis, and Characterization of Dirhodium(II,II) Complexes As Sensitizers: Tandem Experimental and Theoretical Studies

Abstract

This dissertation focuses on the design, synthesis, and characterization of dirhodium complexes as sensitizers for dye-sensitized solar cells, as photoactivated chemotherapeutic drugs, and as photocatalysts for Hv2 production with low-energy light. Thorough experimental and computational studies of their structural and photophysical properties were performed in order evaluate their suitability for a variety of applications. Coordination of partial-paddlewheel complexes through the axial positions in a step-wise manner led to the synthesis of a new class of dirhodium complexes, namely cis- [Rhv2(AcO)v2(qxnp)(MeCN)v3][BFv4]v2 and cis-[Rhv2(AcO)v2(qxnp)v2][BFv4]v2 (where qxnp = 2- (1,8-naphthyridin-2-yl)quinoxaline). These complexes display appropriate molar absorption coefficients for photoactivated chemotherapy and equatorial solvent molecules that can be photoreleased upon irradiation. The resulting aqua complexes were shown to be able to bind to ds-DNA upon visible light irradiation opening a door to a new class of compounds with potential anticancer properties. Changing the acetate bridging ligands for a more electron rich formamidinate ligand led to the synthesis of a series of three new axially-blocked complexes of the form cis-[Rhv2(DTolF)v2(L)v2][BFv4]v2 (DTolF = N,N'-di-p-tolylformamidinate and L = axially blocking ligand) with improved photophysical properties when compared to the axially free analogues. These complexes display panchromatic absorption profiles and relatively long-lived excited states necessary for electron-transfer reactions. These represent the first class of dirhodium complexes capable of accepting an electron from p-phenylenediamine with low energy light which makes them ideal candidates for p-type sensitization. A step-wise reaction of qxnp and the partially solvated complex cis- [Rhv2(DTolF)v2(MeCN)v6][BFv4]v2 led to the synthesis of the firs examples of trans dirhodium formamidinate complexes reported in the literature, trans-[Rhv2(DTolF)v2(qxnp)(MeCNv)3- ][BFv4]v2 and trans-[Rhv2(DTolF)v2(qxnp)v2][BFv4]v2. The latter displays a red-shifted absorption spectrum when compared to the cis analogue and can also partake in electron transfer reactions upon irradiation with low energy light. This new synthetic methodology could facilitate the synthesis of a new class of supramolecular architectures with interesting photophysical properties. Asymmetric complexes were also synthesized from the reaction of cis- [Rhv2(DTolF)v2(MeCN)v6][BFv4]v2, qxnp, and np (1,8-naphthyridine). The complexes obtained are able to photocatalyze Hv2 production upon 655 nm excitation which is a vast improvement over previously published dirhodium complexes. The research presented in this dissertation expands on the current dirhodium chemistry literature as sensitizers for a variety of applications.