Theoretical investigation on electronic structure and luminescent properties of 6-phenyl-4-(p-R-phenyl)-2,2′-bipyridyl (R = Me, COOMe, P(O)(OEt)₂) (C_̂N_̂N) platinum(II)R′(R′ = Cl or CCPh) complexes

Quantum chemical method was used to investigate the geometrical structures, electronic properties, absorption and phosphorescent mechanism of four Pt(II) complexes 6-phenyl-4-(p-R-phenyl)-2′,2-bipyridyl (C^N^N)Pt(II)Cl, (R = Me, (1a); COOMe (1b), P(O)(OEt)₂ (1c), and 6-phenyl-4-(p-Me-phenyl)- 2′,2-bipyridyl (C^N^N)Pt(II) CCPh (2a). The geometrical structures and electronic properties of 1a-1c are insensitive to the variation of substituents, because of their longer distance to Pt(II) center. However, changes are significant for 2a with respect to 1a due to the direct connection of CCPh group with phosphorescent Pt(II) center. The oscillator strengths of the lowest energy absorptions for 1a-1c are small, and this intensity for 2a gets a remarkable enhancement due to the increase of electronic delocalization on the acetylide and Pt(II). More importantly, different phosphorescent quantum yields of these complexes are compared, especially between 1a and 2a. It is believed that the higher e_g*-like Pt d-orbital, the larger ³MC-³MLCT energy gap as well as the deeper potential energy surface (PES) of 2a than 1a are the main reasons accounting for its higher efficiency of 2a. In addition, the potential as light-emitting layer materials of these complexes are investigated.