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

A series of tridentate cyclometalated platinum(II) complexes ((CN)-N-Lambda*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 (CNN)-N-Lambda-N-Lambda platinum complexes with a fused five-five-membered metallacycle, the platinum coordination in (CN)-N-Lambda*N complexes is much clo:;er to a square planar geometry. The photophysical properties of the complexes were studied. The geometrical change from (CNN)-N-Lambda-N-Lambda to (CN)-N-Lambda*N led to a substantial improvement in phosphorescence efficiency of the complexes with En acetylide ligand in solution at room temperature. For example, the quantum yield of ((CN)-N-Lambda*N)PtCCPh was measurec to be 56%, demonstrating a big jump from 4% reported for ((CNN)-N-Lambda-N-Lambda)PtCCPh.