Near-infrared absorption carboxylated chlorophyll-a derivatives for biocompatible dye-sensitized hydrogen evolution

Abstract Chlorophylls (Chls) are naturally occurring photosensitizers having an excellent visible and near-infrared light absorption property. Herein, we employ three Chl a derivatives as sensitizers in a TiO 2 -based photocatalytic system for H 2 evolution with ascorbic acid as the sacrificial reagent under visible light (λ > 400 nm). The H 2 -evolution activity of these Chl a derivatives depends on a carboxy group in the C3- and/or C17-substituent(s). The concentration of 1 mg/ml dye/Pt/TiO 2 powder suspended in an aqueous solution with ascorbic acid as the sacrificial reagent gives the highest H 2 -evolution rate. The fact that Chl-2 with a carboxy group on the C3 position of the chlorin macrocycle gives the highest H 2 -evolution rate of 0.79 μmol h −1 is ascribed to the lowest charge recombination rate between Chl-2 and TiO 2 among all Chls investigated. This work provides us with important information in synthesizing more favorable molecular structure of Chl derivatives for the highly efficient photocatalytic H 2 evolution from water splitting.