Synthesis, crystal structure, photophysical property and electropolymerization of Pt(II) complexes with carbazole-grafting 2-(2-pyridyl)benzimidazole

Two neutral-charged Pt(II) complexes, i.e., [(PBC)PtCl2] (5) and [(PBC)Pt(C ≡ CC6H5)2] (6) (PBC = N-[4-(9-carbazole)butyl]-2-(2-pyridyl)benzimidazole) have been synthesized and verified by 1H NMR and X-ray crystallography. In each of them, the coordinate geometry of Pt atom is a distorted square planar configuration with bond distances and angles in the normal range. Complex 6 shows an intense metal-to-ligand charge transfer (1MLCT) (dπ(Pt) → π*(L)) transition at 412 nm in the UV-Vis absorption spectrum and a strong phosphorescence at 593 nm in CH2Cl2 solution at ambient temperature. By selective optical-stimulation at 320 nm, an incomplete intramolecular energy transfer process from the carbazole unit to the [(PB)Pt(C ≡ CC6H5)2] center results in unbalanced dual-emissive bands of a quenched carbazole-based luminescence in deep blue region and an orange 3MLCT emission with increasing intensity. The introduction of carbazole unit also triggers the electropolymerization of ligand PBC and complexes 5 and 6. The as-formed polymer film from complex 5 has good conductivity, stability and clear anodic coloration effect.