Red Absorbing Cyclometalated Ir(III) Diimine Photosensitizers Competent for Hydrogen Photocatalysis.

Two new cyclometalated Ir(III) diimine complexes were used as photosensitizers for homogeneous hydrogen evolution reaction (HER). These complexes were characterized by electrochemistry, ultraviolet-visible absorption, time-resolved and steady-state photoluminescence spectroscopy as well as by theoretical methods. The metal-ligand-to-ligand charge transfer character of their lowest excited state was shown to be competent for efficient H 2 photoproduction in the presence of [Co(dmgH) 2 (py)Cl] as the hydrogen evolution catalyst, triethanolamine as the sacrificial electron donor, and HBF 4 as the proton source. Under optimized experimental conditions, both complexes displayed HER over a period of more than 90 h, with turnover numbers reaching up to 11,650, 10,600, and 174 mol H2 mol PS -1 under blue-, green-, and red-light irradiation, respectively. Both complexes showed higher stability and efficiency vs HER than most of the previously described systems of the same kind.