Synthesis, photophysical and electrochemical properties of iridium(III) complexes with 2-aryl-1-phenylbenzimidazoles

A series of mixed-ligand cyclometalated iridium(III) complexes with 2-aryl-1-phenylbenzimidazoles (where aryl is phenyl, 4-chlorophenyl, 4-(N,N-dimethylamino)phenyl, 3,4-dimethoxyphenyl, and 2-thienyl) and 11-carboxydipyrido[3,2-a:2′,3′-c]phenazine have been synthesized and characterized by 1H NMR and 31P NMR spectroscopy and mass spectrometry. The electron absorption spectra (EASs) of the complexes are observed to contain charge-transfer bands in the low-energy region (below 600 nm, ɛ ≈ (1–3) × 103 mol/(L cm)). The bands experience appreciable bathochromic shifts as the electron-donating properties of a benzimidazole ligand strengthen. The complexes manifest luminescence in the yellow-red spectral region. According to alternating current voltammetry data, reversible and quasi-reversible redox transitions (Eox ≈ 1.2–1.7 V with respect to SHE, CH3CN) are observed in solutions of the studied complexes.