Biohybrid solar cells utilizing light absorbing complexes found in natural photosynthesis is an emerging area of research. Particularly, Photosystem I (PSI) is a complex of interest due to its remarkable quantum efficiency which is near unity. Using PSI as the light absorber in solar cells requires an electron mediator that has a midpoint potential (&lt; 400 mV vs. NHE) and solubility (aqueous) properties. Cobalt bipyridine complexes have been well studied in literature as viable replacement mediators to the standard iodide/triiodide redox couple used, which is both corrosive to electrodes and denaturing to proteins such as PSI. Variations on the bridging ligands of these cobalt complexes are being explored as new options for more water-soluble redox mediators. The focus of this project is to explore the synthesis of asymmetric cobalt complexes bearing ligands with different electron-donating and water solubilizing functional groups. This may allow a fine tuning of both redox and solubility properties. In previous research, polyethyleneglycol-1,10-phenathroline (peg-phen) ligands as well as dihydroxy-1,10-phenanthroline (dihydroxy-phen) ligands were complexed with cobalt(II) chloride hexahydrate to yield symmetrical water-soluble cobalt complexes. Electrochemistry was conducted on these complexes and showed very negative redox potentials because of the electron donating nature of -PEG and -OH groups on the ligands. Therefore, asymmetrical complexes are being explored as a possible means to adjust the redox potentials more positive while still keeping the water solubility properties. Cyclovoltammetry, UV-Vis, and <sup>1</sup>H-NMR data of a series of asymmetrical cobalt complexes will be presented. PSI re-reduction kinetics data of suitable cobalt complexes from our synthesized series will be presented.

Synthesis of asymmetrical cobalt complexes: Redox mediators in biohybrid dye sensitized solar cells

2019 Fall National Meeting

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