Ferrocene-Mediated Photochemical Reduction of Naphthol to Generate Hydrogen

The storage of solar energy in chemical bonds can be achieved utilizing more sustainable first row transition metals and organic compounds. Here we show that the weak acid, 7-bromonaphthol, can generate H₂ upon photoexcitation and subsequent electron transfer mediated by ferrocene under photochemical and photoelectrochemical conditions. Evidence is presented to show that near visible, UV-light absorption by 7-bromonapthol generates an excited-state molecule that is reductively quenched by ferrocene. UV-visible spectroscopy shows the buildup of ferrocenium, and gas chromatography shows the generation of H₂ when an acetonitrile solution of 7-bromonaphthol and ferrocene are irradiated with 365 nm light. This reactivity can be translated to photoelectrochemical conditions. In the presence of 7-bromonaphthol in acetonitrile, carbon electrodes modified with ferrocene exhibit higher current responses compared to unmodified carbon electrodes at an applied potential of just −0.3 V versus the saturated calomel electrode (SCE). These results highlight the ability of ferrocene to mediate electron transfer to the naphthol molecule and the possibility to translate this reactivity into photoelectrochemical devices.