The effect of phenyl group on the electronic and phosphorescent properties of cyclometalated analogues of platinum(II) terpyridine complexes: a theoretical study

Abstract

In this work, we theoretically investigate the effect of phenyl group on the electronic and phosphorescent properties of cyclometalated platinum(II) complexes, thereby designing an efficient blue emitting material. Three platinum(II) complexes Pt(N^N^N)Cl (N^N^N = terpyridine), Pt(N^C^N)Cl (N^C^N = 1,3-di(2-pyridyl)-benzene) and Pt(N^N^C)Cl (N^N^C = 6-phenyl-2,2′-bipyridines) are chosen as the models. Their electronic and phosphorescent properties are investigated utilizing quantum theoretical calculations. The results reveal that the phenyl group significantly affects the molecular and electronic structures, charge distribution and phosphorescent properties. The coordination bond length trans to phenyl group is the longest among the same type of bonds owing to the trans influence of phenyl group. Moreover, the phenyl group largely restricts the geometry relaxation of cyclometalated ligand. The strong σ-donor ability of Pt–C bond makes more electrons center at Pt atom and the fragments trans to phenyl group. In comparison with Pt(N^N^N)Cl and Pt(N^N^C)Cl, the complex Pt(N^C^N)Cl has the smallest excited-state geometry relaxation and the biggest emission energy and spatial overlap between the transition orbitals in the emission process. As a result, Pt(N^C^N)Cl has the largest emission efficiency, which well agrees with the experimental observation. Based on these calculation results, a potentially efficient blue-emitting material is designed via replacing pyridine groups in Pt(N^C^N)Cl by 3-methylimidazolin-2-ylidene.