Photoelectrochemical oxidation of a turn-on fluorescent probe mediated by a surface MnII catalyst covalently attached to TiO2 nanoparticles

•H2DCF is an effective fluorescence sensor to evaluate anode performance in photocatalytic cells.•We show that increased photocurrent does not necessarily correlate with increased catalysis.•Redox-active Mn photoanodes outperform redox-inactive Zn anodes.

A manganese complex covalently attached to a TiO2 electrode via a light-absorbing organic linker (L) was used in the photooxidation of 2′,7′-dihydrodichlorofluorescein (H2DCF). Significant and sustained photocurrent was observed upon visible-light illumination of the fully assembled anode in the presence of the substrate. The two-electron, two-proton oxidation of H2DCF yields the fluorescent compound, 2′,7′-dichlorofluorescein (DCF). Our studies suggest that the MnII–L–TiO2 architecture is an effective photoanode for multielectron chemistry, as production of DCF under visible-light illumination exceeds yields observed for bare TiO2 as well as ZnII–L–TiO2 anodes. The turn-on fluorescent behavior of H2DCF upon oxidation makes it an excellent substrate for the study of new photoanodes. The high fluorescence quantum yield of DCF allows for nanomolar sensitivity and real-time monitoring of substrate oxidation.

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