Highly efficient blue-emitting of bis-cyclometalated tetravalent platinum (IV) complexes: A theoretical study

Abstract

Pt(IV) complexes bespeak the prospect as phosphorescent materials because of their excellent properties, whereas the reports of excavating potential properties for Pt(IV) complexes in phosphorescence are limited. To address this issue, a DFT/TDDFT calculation has been applied on two series of biscyclometalated Pt(IV) complexes ([Pt(ppy)2XCl], where X = -CH3(1-Me); -CF3(1a-CF3); -CN(1a-CN), -(CH3)3 (1b-tBu); -CH2NH2(1b-AMe); -C6H5(2-Ph); -C6F5(2a-C6F5) and -2,4,6-(CH3)3C6H5 (2b-Mes)) to shed light on the effects of systematic single monodentate ancillary ligand modifications on structure and photophysical properties. The calculated results confirm that all complexes displayed blue emission in dichloromethane solution with varying emission efficiencies that were found to be influenced by the electronic nature of the ancillary ligand. The stronger the electron-releasing ability and the smaller degree of extended conjugation in the monodentate ancillary ligand can give rise to intensive the radiative decay. Regardless of whether π conjugation exists or not, increasing electron-withdrawing character in ancillary ligand of parent complexes 1-Me ([Pt(ppy)2CH3Cl]) or 2-Ph ([Pt(ppy)2C6H5Cl]) can be unbeneficial for the nonradiative decay process. In addition, the results demonstrate that complexes 1a-CN ([Pt(ppy)2CNCl]) exhibits a better blue phosphorescent material with a higher quantum yield.So far, there has been no theoretical study that systematically focuses on biscyclometalated Pt(IV) complexes. Our research provides a strong impetus to further optimize the phosphorescence efficiencies based on Pt(IV) complexes.