Synthesis and physico-chemical studies of cyclometalated heteroleptic iridium(III) complexes

Phosphorescent studies of 2-arylimidazole heteroleptic cyclometalated iridium(III) complexes with picolinic acid as the ancillary ligand were made. The observed experimental data reveals that these complexes possess dominantly 3MLCT and 3π–π* excited states and the solvent shift of these complexes are 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 λemi.

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► 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.