Clarifying the Active Site Role of meso‐Carboxyphenyl Group for Free Base Porphyrins in Photocatalytic H2 Evolution Reaction

Abstract

AbstractThree kinds of free base meso‐carboxyphenylporphyrins were compared about their photocatalytic activity to elucidate the role of −COOH group playing in H2 evolution from water splitting. Meso‐tetra(3,5‐dicarboxyphenyl)porphyrin (H2TDCPP) gives a much larger H2 evolution rate than other two porphyrins, attributable to more −COOH groups involved that may interact with H2O. This interaction, as revealed by DFT calculation, initiates H2 evolution from the splitting of associated H2O under ultraviolet light irradiation resulted by effective transfer of photogenerated electron from central porphine ring to meso‐substituents and then further to the interacted water. Improving the accessibility of −COOH groups to water molecule by optimizing H2TDCPP dosage induces an H2 evolution rate around 31.21 mmol ⋅ h−1 ⋅ g−1 (pH=7, full‐spectrum light), which is unprecedented for free based porphyrin photocatalysts without metal‐cocatalysts. This work clarifies the active site role of −COOH groups and paves a new way to design high‐performed organic photocatalysis by introducing polar groups‐based active sites.