Theoretical investigation on the effect of ancillary ligand modification for highly efficient phosphorescent platinum(ii) complex design

Abstract

In this study, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were employed to investigate the geometries, electronic structures, reorganization energy (λ) and photophysical properties of four cyclometalated Pt(II) complexes (bzq)Pt(dpm) (1), (bzq)Pt(ppy) (2), (bzq)Pt(Ncaz) (3) and (bzq)Pt(Ndbt) (4) (where bzq = benzo[h]quinoline, dpm = dipivolylmethanoate, ppy = 2-phenylpyridine, Ncaz = N-substituted carbazole and Ndbt = N-substituted dibenzothiophene). In addition, the radiative decay processes and zero-field splitting were calculated based on the spin–orbit coupling (SOC) effect, and nonradiative decay pathways were discussed to evaluate the phosphorescence efficiency qualitatively. All the complexes retain the bzq as a cyclometalated ligand and our research focuses on the role recognition of another ancillary ligand modification theoretically. According to the results, in complexes 2–4 replacing the dpm with different ligands shows better rigidity which may weaken the nonradiative decay pathways and enhance the capability of charge transfer. Furthermore, complexes 1–4 tend to be bluish-green luminescent materials, and the emission wavelengths of 1, 2 and 4 are close to each other due to the similar excited state energy levels and electronic density distribution. Compared with complex 1, the radiative decay rate constants (k_r) of 2–4 are greatly increased. Therefore, the designed complexes would be potential phosphorescence materials because of their high phosphorescence quantum efficiency and complex 3 can also serve as a promising bipolar transporting material due to its better charge transfer balance character.