Amplification of circularly polarized luminescence from chiral cyclometalated platinum(II) complexes by the formation of excimer

Circularly polarized organic light-emitting diodes (CP-OLEDs) have raised increasing interests owing to their potential application in next-generation displays. In this work, by introducing chiral alkyl chain into tridentate chelating ligand 2,6-bis(N-alkylbenzimidazol-2’-yl)benzene, three chiral Pt(II) complexes are successfully designed and synthesized. All the complexes exhibited bright green emission in dilute acetonitrile solution, while strong yellow-orange emission in highly concentrated solution. However, when these complexes are doped into polymer polymethyl methacrylate, the green emission stemmed from the intrinsic single molecule would be changed into red emission from excimer through adjusting the doping levels. More importantly, the CPL signals could be amplified by an order of magnitude in comparison with solution state. Furthermore, the monochrome devices based on these complexes were successfully fabricated, and achieved good device performances with the maximum luminance of up to 1720 cd m−2 and electroluminescence dissymmetry values of around 2.6 × 10−3. These results indicate that such design strategy for Pt(II) complexes with tridentate cyclometalled ligands would be important for the development of high-performance CP-OLEDs.