Charge-Transfer-to-Solvent Photochemistry of Electrode-Confined Ferrocene- and Cobaltocene-Based Polymers: Photoelectrochemical Reduction of Halocarbons

Abstract

Like the metallocenes themselves, metallocene-based polymers exhibit near-UV charge-transfer-to-solvent (CTTS) absorption in the presence of CCl{sub 4}, CHCl{sub 3}, CH{sub 2}Cl{sub 2}, CBr{sub 4}, and CHBr{sub 3}. The photoelectrochemistry of charge transfer complexes of two ferrocene-containing polymers and one cobaltocene-containing polymer has been studied. When the metallocene-based polymer is confined to the surface of an electrode that is held at a potential negative of the formal potential of the metallocene, near-UV excitation results in sustained cathodic current in electrolyte solutions containing halocarbons. The wavelength, acceptor, and potential dependences are in accord with a sustained current that is due to a metallocene-to-halocarbon CTTS absorption where the photoprocess results in the reduction of the halocarbon at an electrode potential significantly positive of where electrochemical reduction occurs in the dark. The octamethylferrocene-based system shows a more negative potential onset and a longer wavelength offset of photocurrent than the simple ferrocene-based system, consistent with the electron-releasing nature of the methyl substituents. The onset of photocurrent in the cobaltocene-based system occurs at the most negative potential of the three, consistent with the cobaltocene-based system having the most negative formal potential of the metallocenes studied. 13 refs., 5 figs., 1 tab.