Efficiently luminescent heteroleptic neutral platinum(ii) complexes based on N^O and N^P benzimidazole ligands

Abstract

A series of new luminescent cycloplatinated(II) complexes (5a–8a and 5b–8b) with formulas Pt(bt)(N^O) and Pt(bt)(N^P) have been synthesized [bt = phenylbenzothiazole, N^O = (2-(1H-benzimidazole)-phenyl)diphenylphosphine oxide derivatives for 1a–4a and N^P = (2-(1H-benzimidazole)-phenyl)diphenylphosphine derivatives for 1b–4b]. The crystal structures of the complexes show distorted square planar geometries around the platinum centers. There are no obvious π–π and Pt–Pt intermolecular interactions in the crystal lattice due to the presence of sterically bulky ancillary ligands. Consequently, these complexes exhibit structured monomeric emissions in the range of 527–540 nm in CH₂Cl₂ solution. The photoluminescent quantum yields of Pt(bt)(N^O) (5a–8a) in CH₂Cl₂ solution at room temperature are higher than those of Pt(bt)(N^P) (5b–8b). The above result is well consistent with the crystal structural characteristics of the complexes. The structured emission with microsecond radiative lifetimes and the result of TD-DFT calculations indicate that the emissions of these complexes are mainly attributed to a mixed ³LC-MLCT state.