Accesses to electronic structures and the excited states of iridium complexes containing pyrazolyl or benzimidazoly ligands: A DFT/TDDFT exploitation

The ground state, 3MLCT and 3MC excited states of two Ir complexes Ir(dfbpzb)(ppy)Cl (1) and Ir(Mebib)(ppy)Cl (2) where dfbpzb = 1,5-difluore-2,4-bis(3-methylpyrazolyl)benzene, ppy = 2-phenylpyridine, and Mebib = bis(N-methylbenzimidazoly)benzene, have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The substitution from dfbpzb ligand to Mebib ligand induces a significant change on the luminescent properties of complexes 1 and 2. The complex 1 does not emit at room temperature, while complex 2 does. The UV–Vis absorption spectra of both complexes are well reproduced by TD-DFT calculations. Importantly, the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) states were discussed in detail by excited state calculations, and the 3MLCT → 3MC deactivation pathway was demonstrated as an important factor for the lack of emission for the investigated complex 1.