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 H-2 production. The para-substituted isomer, ZnT(p-NI)PP delivered a much higher H-2 production rate (H-2) of 973 mol g(-1) h(-1) compared to that of meta- and ortho-substituted isomers, ZnT(m-NI)PP (597 mol g(-1) h(-1)) and ZnT(o-NI)PP (54 mol g(-1) h(-1)), respectively. The ZnTPP produced H-2 of 7 mol g(-1) h(-1), which is 200 times lower than the ZnT(p-NI)PP. The highest H-2 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.