Decomposition of water over Picene-derivatized photocatalysts under visible light irradiation

Inorganic semiconductors such as TiO₂ absorb ultraviolet light to promote reactions. However, sunlight consists mainly of visible light, and so the development of photocatalysts that can use visible light is being actively researched. Density functional theory (DFT) calculations previously showed that the introduction of formyl, carboxyl, and carboxyethyl groups into picene can absorb visible light and generate hydrogen via the decomposition of water. In this study, these substituted picene derivatives were employed as photocatalysts, and their water photolysis activities were evaluated under visible light irradiation. All three picene derivatives were active photocatalysts, with hydrogen production activities decreasing in the order of: picene-13-carbaldehyde (CHO-picene) > picene-13-carboxylic acid (COOH-picene) ≈ Ethyl picene-13-carboxylate (COOEt-picene) > picene. Subsequently, the effects of the three functional groups on the hydrogen production activity in the water photolysis reaction were investigated in further detail. The effects of the functional groups were found to be in accordance with the Hammett equation, wherein a greater electron-withdrawing property led to a higher hydrogen production activity.