Dinuclear Iridium(III) Complexes Containing Bibenzimidazole and Their Application to Water Photoreduction

An efficient three-component catalytic system for visible-light-induced production of hydrogen from water was developed based on new dinuclear iridium photosensitizers (PSs), [Ir(tfdpyb)Cl]2(BiBzIm) (P1) and [Ir(tfmppy)2]2BiBzIm (P2) [tfdpyb = 1,3-di(2-pyridyl)-4,6-bis(trifluoromethyl)benzene, tfmppy = 2-(4-(trifluoromethyl)phenyl)-pyridine, BiBzIm = 2,2′-bibenzimidazole]. These iridium complexes were fully characterized by 1H NMR and ESI-MS, and their photophysical properties and electrochemical behaviors were also investigated. To compare with this new type of iridium compounds, the mononuclear analogues Ir(tfdpyb)(BiBzImH)Cl (P3), Ir(tfmppy)2(BiBzImH) (P4), and Ir(dpyx)(BiBzImH)Cl (P5) (dpyx = 1,3-di(2-pyridyl)-4,6-dimethylbenzene) were also synthesized. The absorption spectra of dinuclear and mononuclear complexes are similar mainly in terms of their shape in the visible-light region, but as expected, the dinuclear species are more intense (approximately twice) compared with the corresponding mononucl...