Enhancing photocatalytic hydrogen evolution by intramolecular energy transfer in naphthalimide conjugated porphyrins

Abstract

Three new isomeric naphthalimide conjugated porphyrins, ZnT(p-NI)PP, ZnT(m-NI)PP and ZnT(o-NI)PP are developed for photocatalytic H₂ production. The para-substituted isomer, ZnT(p-NI)PP delivered a much higher H₂ production rate (ηH₂) of 973 μmol g⁻¹ h⁻¹ compared to that of meta- and ortho-substituted isomers, ZnT(m-NI)PP (597 μmol g⁻¹ h⁻¹) and ZnT(o-NI)PP (54 μmol g⁻¹ h⁻¹), respectively. The ZnTPP produced ηH₂ of 7 μmol g⁻¹ h⁻¹, which is 200 times lower than the ZnT(p-NI)PP. The highest ηH₂ of ZnT(p-NI)PP among the isomers could be attributed to the most efficient intramolecular energy transfer from the naphthalimide to the porphyrin ring which further enhanced the electron transfer from the photo-excited porphyrin moiety to the Pt co-catalyst.