Molecular-engineered [Ir(Fppy)2(Mepic)] towards efficient blue-emission

Abstract

A novel Ir(III) complex, [Ir(Fppy)₂(Mepic)] (Fppy = 2-(2,4-difluorophenyl)pyridinate; Mepic = 3-methylpyridine-2-carboxylate) was engineered to show a blue phosphorescence with an impressive unitary quantum yield in our search for luminescent metal complexes for low cost displays and efficient lighting devices. Application of the Golden rule through Franck–Condon spectral analyses along with TD-DFT calculations and comparisons to the [Ir(Fppy)₂(pic)] complex have provided insights on the mixing extension between charge-transfer (CT) and ligand-centered (LC) excited states in the emissive lowest-energy triplet transition for different media. The relatively narrow and vibronically-structured emission of [Ir(Fppy)₂(Mepic)] at 298 K mainly arises from a spin–orbit-induced mixed ³MLCT-LC_{Ir(Fppy)→Fppy}/³LLCT_Fppy→Mepic excited state, with an enhanced MLCT character because of the methyl addition to pic. In frozen media at 77 K, the CT contribution is extinguished, leading to a pure LC_Fppy emission, with a similar emissive spectral profile to the free ligand, FppyH. The efficient blue emission shows that the complex is suitable for high-performance light-emitting devices and for thermo- and rigidity-sensors.