Tuning the emission maxima of iridium systems using benzimidazole-based cyclometallating framework

Abstract

Herein, we describe the development of four mononuclear cyclometallated iridium complexes [1](PF6) - [4](PF6) using alkyl chain appended benzimidazole-based cyclometallting ligands (L1 and L2). The complexes were characterized using different analytical techniques. The crystal structures of [1](PF6), and [2](PF6) reveal the distorted octahedral geometry around iridium center, and the nitrogen donors of the imidazole unit are coordinated with expected trans orientation. The experimental bond parameters are matching with the DFT calculated data. The theoretical investigation further reveals that the HOMO of the complexes is localized on iridium and cyclometallating ligands, and LUMO is formed by bpy/phen unit. All the complexes are emissive with moderate quantum yield at room temperature. Both the absorption and emission maxima are found to be highly dependent on the substituent present on the ligand framework. A significant shift (∼80 nm) of emission maxima is achieved by employing electron withdrawing fluorophenyl unit to π-conjugated thiophene unit. Tuning emission maxima by simple variation of substitution is exciting and would be of great importance in developing luminescent materials.