An Ir(III) Complex Photosensitizer With Strong Visible Light Absorption for Photocatalytic CO(2) Reduction

A cyclometalated iridium(III) complex having 2-(pyren-1-yl)-4-methylquinoline ligands [Ir(pyr)] has a strong absorption band in the visible region (ε(444nm) = 67,000 M(−1) cm(−1)) but does not act as a photosensitizer for photochemical reduction reactions in the presence of triethylamine as an electron donor. Here, 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H) was used instead of the amine, demonstrating that BI(OH)H efficiently quenched the excited state of Ir(pyr) and can undergo the photochemical carbon dioxide (CO(2)) reduction catalyzed by trans(Cl)-Ru(dmb)(CO)(2)Cl(2) (dmb = 4,4′-dimethyl-2,2′-bipyridine, Ru) to produce formate as the main product. We also synthesized a binuclear complex combining Ir(pyr) and Ru via an ethylene bridge and investigated its photochemical CO(2) reduction activity in the presence of BI(OH)H.