Synthesis and characterization of phosphorescent cyclometalated iridium complexes containing 2,5-diphenylpyridine based ligands

A series of phosphorescent cyclometalated iridium complexes with 2,5-diphenylpyridine-based ligands has been synthesized and characterized to investigate the effect of the simple ligand modification on photophysics, thermostability and electrochemistry. The complexes have the general structure (C<^>N)(2)Ir(acac), where C<^>N is a monoanionic cyclometalating ligand [e.g. 2,5-diphenylpyridyl (dppy), 2,5-di(4-methoxyphenyl)pyridyl (dmoppy), 2,5-di(4-ethoxyphenyl)pyridyl (deoppy) and 2,5di(4-ethylphenyl)pyridyl (deppy)]. The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The (dppy)(2)Ir(acac) has been characterized using X-ray crystallography. Calculation on the electronic ground state of (dPPY)(2)Ir(acac) was carried out using B3LYP density functional theory. The highest occupied molecular orbital (HOMO) level is a mixture of Ir and ligand orbitals, while the lowest occupied molecular orbital (LUMO) is predominantly dppy ligand-based. Electrochemical studies showed the oxidation potentials of (dmoppy)(2)Ir(acac), deoppy)(2)Ir(acac), (deppy)(2)Ir(acac) were smaller than that of (ppy)(2)Ir(acac), while the oxidation potential of (dppy)(2)Ir(acac) was larger relative to (ppy)(2)Ir(acac). The 10% weight reduction temperatures of these complexes were above that of (ppy)(2)Ir(acac). All complexes exhibited intense green photoluminescence, which has been attributed to MLCT triplet emission. The maximum emission wavelengths in CH2Cl2 at room temperature were in the range 531-544 nm, which is more red-shifted than that of (ppy)(2)Ir(acac). Copyright (c) 2005 John Wiley & Sons, Ltd.