Iridium(III) 2-Phenylbenzimidazole Complexes: Synthesis, Structure, Optical Properties, and Applications in Dye-Sensitized Solar Cells

A series of bis‐cyclometalated iridium(III) complexes, [Ir(LH)₂(H₂dcbpy)][PF₆] (1), [Ir(LMe)₂(H₂dcbpy)][PF₆] (2), and [Ir(LPh)₂(H₂dcbpy)][PF₆] (3), where LH = 1‐H‐2‐phenylbenzimidazole, LMe = 1‐methyl‐2‐phenylbenzimidazole, LPh = 1,2‐diphenylbenzimidazole, and H₂dcbpy = 2,2′‐bipyridine‐4,4′‐dicarboxylic acid, has been synthesized and fully characterized by elemental analysis, ¹H and ³¹P NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray analysis. The complexes show strong luminescence in the yellow–orange region in ethanol at room temperature (quantum yield is up to 22 %), and absorb light up to 550 nm with molar absorptivities of 1500–2000 M^–1 cm^–1. Complexes 1 and 2 possess very similar optical properties, whereas the introduction of the phenyl ring (complex 3) causes a hypsochromic shift (≈ 30 nm) of the luminescent maximum as well as resulting in an almost 50 % increase in the extinction coefficient at 490 nm compared with 1 and 2. A dye‐sensitized solar cell (DSSC) based on complex 3 exhibits a short‐circuit photocurrent of 2.8 mA cm^–2, an open‐circuit photovoltage of 0.44 V, and a power conversion efficiency of 0.7 %.