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

Citations Over TimeTop 10% of 2014 papers

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 ligands. All complexes are emissive in solutions at room temperature and in glassy matrix at 77 K. The emitting states are assigned to 3π,π* (C^N ligand localized) /3MLCT for 1, 3π,π*/3MLCT/3LMCT (ligand-to-metal charge transfer) for 2–4, pure 3π,π* transitions for 5 and 6, and 3π,π*/3MLCT/3LMCT/3LLCT for 7. Complex 5 possesses the lowest emission energy because the larger conjugation and the most delocalized character of the 3π,π* transition within the C^N ligand in this complex. Complexes 1, 4, and 7 possess larger contribution of charge transfer characters in their lowest triplet excited states. Therefore, the transient absorption of these three complexes is broad but short-lived (90–300 ns). In contrast, complexes 2, 3, 5, and 6 all give long-lived (2.0–19.5 μs) triplet transient absorption in the visible spectral region of ca. 450–700 nm, which can be regarded as emanating predominantly from the C^N ligand-centered 3π,π* state. The reverse saturable absorption (RSA) of these complexes was evaluated at 532 nm for nanosecond laser pulses. The results demonstrate that these complexes, except for 7, all exhibit strong RSA for nanosecond laser pulses at 532 nm, with a trend of 7 < 1 < 4 < 6 < 5 ≈ 2 ≈ 3.

Related Papers

• → Review on Anionic/Cationic Surfactant Mixtures(2007)299 cited
• → Molecular forms of rhodamine B(1981)138 cited
• → New sequential treatment for mature landfill leachate by cationic/anionic and anionic/cationic processes: Optimization and comparative study(2010)63 cited
• Influence of Gemini Cationic Surfactants for the Dyeing Property of Modified Polyester Fibers(2010)
• Formulation of Co-cationic Fatliquor for Leather and Determination of Its Properties(1999)