Improvement in Phosphorescence Efficiency through Tuning of Coordination Geometry of Tridentate Cyclometalated Platinum(II) Complexes

A series of tridentate cyclometalated platinum(II) complexes (C∧N*N)PtL (L = Cl or acetylide) featuring a fused five-six-membered metallacycle were synthesized. The structure of the complexes was confirmed by X-ray crystallography. In contrast to the C∧N∧N platinum complexes with a fused five-five-membered metallacycle, the platinum coordination in C∧N*N complexes is much closer to a square planar geometry. The photophysical properties of the complexes were studied. The geometrical change from C∧N∧N to C∧N*N led to a substantial improvement in phosphorescence efficiency of the complexes with an acetylide ligand in solution at room temperature. For example, the quantum yield of (C∧N*N)PtCCPh was measured to be 56%, demonstrating a big jump from 4% reported for (C∧N∧N)PtCCPh.