Molecular Copper(I)‐Sensitized Photoanodes for Alcohol Oxidation under Ambient Conditions

Dye‐sensitized photoelectrochemical cells can enable the production of molecules currently accessible through energetically demanding syntheses. Copper(I)‐based dyes represent electronically tunable charge transfer and separation systems. Herein, we report a Cu(I)‐bisdiimine donor‐chromophore‐acceptor dye with an absorbance in the visible part of the solar spectrum composed of a phenothiazine electron donor, and dipyrido[3,2‐a:2′,3′‐c]phenazine electron acceptor. This complex is incorporated onto a zinc oxide nanowire semiconductor surface effectively forming a photoanode that is characterized spectroscopically and electrochemically. We investigate the photo‐oxidation of hydroquinone, and the photosensitization of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl and N‐hydroxyphthalimide for the oxidation of furfuryl alcohol to furfuraldehyde, resulting in near quantitative conversions, with poor selectivity to the alcohol. A donor‐Cu(I)‐acceptor visible light photosensitizer is synthesized and characterized. Upon light irradiation, an electron/hole pair is formed first by metal‐to‐ligand charge transfer. The ligands are tailored such that the hole is delocalized into a phenothiazine donating moiety, and the electron is delocalized in a phenazine accepting moiety, leading to a charge separated state, capable of driving photoelectrochemical reactions.