Nonlinear Absorbing Cationic Bipyridyl Iridium(III) Complexes Bearing Cyclometalating Ligands with Different Degrees of π-Conjugation: Synthesis, Photophysics, and Reverse Saturable Absorption

Abstract

We report the synthesis, photophysics, and reverse saturable absorption together with time-dependent density functional theory modeling of seven cationic iridium(III) complexes bearing one 2,2′-bipyridine ligand and two cyclometalating ligands (C^N ligand) with varied degrees of π-conjugation (HC^N = benzo[H]quinoline in 1, 1-phenylisoquinoline in 2, 1-(2-pyridyl)naphthalene in 3, 2-(2-pyridyl)naphthalene in 4, 1-(2-pyridyl)pyrene in 5, 1,2-diphenyl-pyreno[4,5-d]imidazole in 6, and 3-(2-pyridyl)perylene in 7). All complexes possess ligand-localized 1π,π* transitions as the major absorption bands and lower-energy 1MLCT (metal-to-ligand charge transfer)/1LLCT (ligand-to-ligand charge transfer) transitions in their ultraviolet–visible absorption spectra. The extended π-conjugation in the cyclometalating ligands of complexes 5–7 causes a significant red-shift of the major absorption bands with increased molar extinction coefficients with respect to those of complexes 1–4 that contain less conjugated C^N ligan...