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

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.