Influence of restricted rotation of small-sized substituent on phosphorescence efficiency for Pt(II) complexes: A theoretical investigation

Herein, the radiative and non-radiative decay processes of six carborane-based Pt(II) complexes were explored with the help of the density functional theory and time-dependent density functional theory. In order to interpret the influence of non-metal heavy atoms on the phosphorescent quantum yields, the determined factors, i.e., the ZFS (zero-point filed splitting) parameters, radiative decay rate constants and photodeactivation mechanisms, were unveiled. The results indicate that the spin-orbital coupling effects can be slightly regulated via introducing the non-metal heavy atoms into the carborane. Also, the non-metal heavy atoms substituents could cause slightly decrease of the energy barriers between the (ES)-E-3 and (MC)-M-3 excited states, and thus, for Pt-6, a fast non-radiative decay process may occur. Moreover, compared with the Pt-1, the rotation of methyl in Pt-2 similar to 5, can be effectively restricted with the aid of hydrogen bonding and halogen bonding, which is beneficial for obtaining small non-radiative decay rate constants. Accordingly, it provides a strategy for realizing the restriction of small group rotation to achieve the high-efficient phosphorescent emitters.