Tuning the photophysical and electrochemical properties of iridium(III) 2-aryl-1-phenylbenzimidazole complexes

A series of heteroleptic bis-cyclometalated iridium(III) complexes, [Ir(cpbi)(2)(H(2)dcbpy)][PF6] (1), [Ir(pbi)(2)(H(2)dcbpy)][PF6] (2), and [Ir(mpbi)(2)(H(2)dcbpy)][PF6] (3), where pbi = 1,2-diphenylbenzimidazole, cpbi = 2-(4-chlorophenyl)-1-phenylbenzimidazole, mpbi = 2-(3,4-dimethoxyphenyl)-1-phenylbenzimidazole, and H(2)dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid has been synthesized and characterized by elemental analysis, H-1, P-31 NMR, and high resolution mass-spectra. Molecular structure of complex 3 has been determined from single-crystal X-ray analysis. The complexes exhibit absorption up to 550 nm with molar absorptivities of 2500 M (1) cm (1). They have strong luminescence in broad yellow-to-red region in solutions at room temperature. While chloro-substituent (complex 1) causes a little hypsochromic shift of the absorption maxima compared to unsubstituted 2, introduction of two methoxy-groups (complex 3) gives rise to a bathochromic shift of about 100 nm. Alternating current voltammetry studies of the complexes indicates reversible oxidation and reduction potentials. Calculated excited state oxidation potentials for 1-3 are negative enough to efficiently inject electrons into the conduction band of TiO2 (EF approximate to -0.5 V). Thus, from the electrochemical point of view, all the complexes, especially 3, are good candidates for operation in DSSC as dyes. (C) 2014 Elsevier B.V. All rights reserved.