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

A series of new luminescent cycloplatinated(II) complexes (5a-8a and 5b-8b) with formula 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 527-540 nm in CH2Cl2 solution. The photo-luminescent quantum yields of Pt(bt)(N^O) (5a-8a) in CH2Cl2 solution at room temperature are higher than that of Pt(bt)(N^P) (5b-8b). The above result is well coincident with the crystal structure characteristics of the complexes. The structured emission with microsecond radiative lifetimes and the support of TD-DFT calculations indicate that the emissions of these complexes are mainly attributed to a mixed 3LC-MLCT state.