Blue phosphorescent Zn(ii) and orange phosphorescent Pt(ii) complexes of 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyrimidine

Abstract

To investigate the different phosphorescent promoting effects of organic emitters by various metal centers, a new ligand, 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyrimidine (pmbp), and its Zn(II), Hg(II), and Pt(II) complexes, [Zn(pmbp)₂](ClO₄)₂ (1), Pt(pmbp)Ph₂ (2), Zn(pmbp)Cl₂ (3), and Hg(pmbp)Cl₂ (4) were synthesized. Their structures were determined by single crystal X-ray diffraction. The zinc complexes 1 and 3 exhibit blue luminescence in the solid state at ambient temperature, but the mercury complex 4 is not luminescent. At 77 K, both pmbp and complex 1 have blue emissions in MeOH solutions, which were demonstrated to be phosphorescence by their long decay lifetime (μs). By comparing the luminescent properties of the free ligand and the complex, we concluded that the phosphorescence of 1 originates from ligand centered π → π* transitions. Complex 2 exhibits orange luminescence both in CH₂Cl₂ solution at 77 K and in the solid state at ambient temperature, which was assigned to metal-to-ligand [d_M → π*(pmbp)] charge transfer (MLCT). The different origin of luminescence is responsible for the different luminescent color of the Zn(II) and Pt(II) complexes.