Photophysical Properties of Highly Efficient Blue-Green Emitting Cationic Iridium (III) Complexes Containing Two 2-Phenylbenzothiazole Ligands and One Diphosphine Ligand

摘要

Two novel phosphorescent heteroleptic cationic Ir(III) complexes, lr(bt)2(dmpe) (Ir1) and Ir (bt)2(dppe) (lr2), where bt is 2-phenylbenzothiazole, dmpe is l,2-bis(dimethylphosphino)ethane, and dppe is 1,2-bis(diphenyl-phosphino)ethane, were designed and synthesized. Their photophysical and electrochemical properties and the X-ray structure of the Irl complex were investigated. The prepared Ir(lII) complexes exhibited blue-green emissions at 503-538 nm with vibronic fine structures in dichloromethane solution and PMMA film, implying that the lowest excited states are dominated by ligand-based ~3π-π~* transitions. The π-acceptor ability of the diphosphine ancillary ligand leads to blue-shift emission. The room temperature photoluminescent quantum yields (PLQYs) of Irl and Ir2 were 52% and 45%, respectively, in dichloromethane solution. These high PLQYs resulted from steric hindrances by the bulky cationic iridium complexes. The crystal structure of Irl was determined by X-ray crystallography, which revealed that central iridium adopted a distorted octahedral structure coordinated with two bt ligands (N^C) and one dmpc ligand (P^P) showing cis C-C and trans N-N dispositions. The bent nature of the dmpe ligand resulted in a relatively wide bite angle of 83.83° of P-Tr-P.