Bifunctional linkers for electron-transport studies

This thesis describes the synthesis and study of two types of electron-transport linkers that were developed to study the flow of electrons through different mediums to complete a circuit. Following a general introduction (Chapter 1), the thesis is divided into two parts: the synthesis, characterization, and study of ruthenium(II) and osmium(II) bipyridyl complexes on TiO2 surfaces for the purposes of making dye-sensitized solar cells (Chapter 2), and the design and synthesis of molecular wires for embedding within hollow core-shell nanotubes developed as components of water oxidation catalysis (Chapter 3). In the first part, several ligand architectures were synthesized into a series of bifunctional poly-pyridyl metal complexes containing at least one dicarboxylic acid bipyridine (dcb) for the purpose of binding to a TiO2 substrate while the thiol-based bipyridine was meant to bind to a platinum nanoparticle. Combined, this three-component set-up was intended to boost the overall efficiency of a dye-sensitized solar cell (DSSC) device, as platinum has been shown to catalyze the I-/I3- redox reaction. The hypothesis was that by incorporating platinum nanoparticles into DSSCs the large overpotential for the I- /I3- redox mediator could be decreased. The first compounds used a di-methyl lipoate bipyridine ligand. Despite showing early promise due to a disulfide protecting group and a convenient one-pot synthesis, the complex proved to be labile and did not offer the option for synthetic modifications. What followed was a di-penta-thiourea bipyridine, which had the advantage of being synthesized via a modular approach. This, however, showed minimal binding affinity towards the PtNP. The final, and successful, ligand architecture was designed using 4-mercaptoaniline as its foundation to produce an asymmetric bipyridine. This proved stable enough to generate ruthenium(II) complexes. The resulting dyes were characterized synthetically and currently are being studied device fabrication. In the second part, organic molecular wires (oligo(p-phenylenevinylene), three aryl units) were synthesized and characterized before being embedded into ultrathin amorphous silica membranes to provide chemical separation of incompatible catalytic environments of CO2 reduction and H2O oxidation while maintaining electronic and protonic coupling between them. Guided by density functional theory (DFT) calculations, four wire derivatives featuring electron-donating (methoxy) and -withdrawing groups (sulfonate, perfluorophenyl) with highest occupied molecular orbital (HOMO) potentials ranging from 1.48 to 0.64 V vs NHE were synthesized and evaluated. Work performed by collaborators demonstrated that visible-light-induced charge flowed from an anchored Ru bipyridyl light absorber across the silica nanomembrane to Co3O4 water oxidation catalyst. Compared with photocurrents of samples without nanomembrane showed that silica layers with optimized wires performed better, where charge transfer rates increase linearly with wire density, with 5 nm–2 identified as an optimal target for future devices.Ph.D.Includes bibliographical reference