Light-emitting materials from cyclometalated heteroleptic iridium(III) complexes—A physicochemical study

Phosphorescent studies of 2-arylimidazole heteroleptic cyclometalated iridium(III) complexes with picolinic acid as the ancillary ligand were made. The observed experimental data reveal that these complexes possess dominantly 3MLCT and 3π–π* excited states and the solvent shift of these complexes is interpreted by Reichardt–Dimroth and Marcus solvent functions. The results are consistent with prior assignments on the absorption band to a metal-to-ligand charge transfer excited state associated with chelating ligand. Emission kinetic studies exploited that the radiative transition (kr) increases with increasing λem.

Synthesis of heteroleptic iridium complex.Figure optionsDownload as PowerPoint slideHighlights
► Bands located at longer wavelength assigned to 1MLCT ← S0 and 3MLCT ← S0 transitions.
► 3MLCT ← S0 is allowed by mixing of spin–orbit coupling.
► 3MLCT ← S0 is close to 1MLCT ← S0.
► Mixing of excited states (LC and MLCT).
► (1E1 − 3E1) increases with decrease in λem, hence, kr increases with increase in λem.