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 (H 2 dcbpy)][PF 6 ] ( 1 ), [Ir(LMe) 2 (H 2 dcbpy)][PF 6 ] ( 2 ), and [Ir(LPh) 2 (H 2 dcbpy)][PF 6 ] ( 3 ), where LH = 1‐H‐2‐phenylbenzimidazole, LMe = 1‐methyl‐2‐phenylbenzimidazole, LPh = 1,2‐diphenylbenzimidazole, and H 2 dcbpy = 2,2′‐bipyridine‐4,4′‐dicarboxylic acid, has been synthesized and fully characterized by elemental analysis, 1 H and 31 P 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 %.