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

•A DFT/TDDFT method was employed to investigate two Ir complexes.•The change of ligand induces a significant change on the luminescent properties.•The 3MLCT → 3MC deactivation pathway is demonstrated.•The lower activation barrier is responsible for the lack of emission.

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.

Graphical abstractTwo Ir complexes containing dfbpzb ligand with pyrazolyl ring (1) and Mebib ligand with benzimidazoly ring (2) have been investigated using the DFT/TDDFT methods. The different photophysical properties of both complexes were rationalized. The lower activation barrier calculated based on the potential energy surfaces of the 3MLCT state is shown to be the principal factor for the loss of room-temperature emission for complex 1.Figure optionsDownload full-size imageDownload as PowerPoint slide