Iridium motif linked porphyrins for efficient light-driven hydrogen evolution via triplet state stabilization of porphyrin

Two new iridium motif linked porphyrins, MBPyZnP-Ir and TBPyZnP-Ir are developed for photocatalytic hydrogen evolution (PHE). The tetra-iridium linked one, TBPyZnP-Ir, displayed the highest H-2 production rate (eta H-2) of 16.12 mmol g(-1) h(-1) within 5 h of irradiation, which is over 2.73-fold higher than MBPyZnP-Ir (5.90 mmol g(-1) h(-1)) and much higher than their precursors TBPyZnP (0.12 mmol g(-1) h(-1)) and MBPyZnP (0.06 mmol g(-1) h(-1)) without iridium. The superior eta H-2 of TBPyZnP-Ir could be explained by the iridium motifs linked to the porphyrin, stabilizing the triplet states of the porphyrin through intramolecular energy transfer; thus enhancing electron transfer from the triplet photo-excited porphyrin moiety to the cobaloxime co-catalyst and consequently proton reduction.