Theoretical Insight Into the Role of Triarylboron Substituents in Tetradentate Dianionic Bis(N-heterocyclic carbene) Platinum(II) Chelates - Improving the Performance of Blue Light Emission

The electronic structures and photophysical properties of eleven Pt-II complexes divided into three series by their degree of conjugation were studied through density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. To investigate the effect of triarylboron substituents and the changes caused by the extension of the conjugation, the nonradiative and radiative decay efficiencies, the geometric relaxations, d orbital splitting, and spin-orbit couplings at the optimized S-0 and T-1 geometries were computed. The results show that complexes with triarylboron substituents may have higher phosphorescence efficiencies than those with cyano groups. Furthermore, complexes with larger conjugation (anthracene groups) may weaken the effects caused by the introduction of triarylboron substituents and are less likely to possess enhanced phosphorescence efficiency. Predictions of the absorption spectra and emission colors indicated that complexes with triarylboron substituents would emit blue colors, whereas the emission colors of the complexes with larger conjugation would be located in the near-infrared region. This work highlights that the introduction of the triarylboron substituents and appropriate conjugation (naphthalene groups) can result in highly efficient phosphorescence in complexes containing donor N-heterocyclic carbene (NHC) ligands.