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 H₂ production rate (ηH₂) 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 ηH₂ 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.