Theoretical investigation of triplet potential energy surfaces for (C^C*) cyclometalated platinum(ii) complexes and the corresponding control strategies

Abstract

Triplet potential energy surfaces, for phosphorescent materials, play a predominant role in determining the radiative and non-radiative decay processes. It is significant and meaningful to explore a promising strategy to control the triplet potential energy surface. In this article, the influence of substituents on the triplet potential energy surface was investigated with the help of density functional theory. In addition, the triplet potential energy surfaces of bimetallic Pt(II) complexes were also explored. The investigated results indicate that for the monometallic Pt(II) complexes, the adiabatic triplet energies of T^bent₁ are located at near 68.66 kcal mol⁻¹. That is, when the adiabatic triplet energy is lower than 68.66 kcal mol⁻¹, by at least 7.22 kcal mol⁻¹, the triplet potential energy surface is constructed with the T^planar₁ configuration. In contrast, the triplet potential energy surface consists of T^planar₁ and T^bent₁ configurations. Thus, it can be regarded as a criterion used to judge the composition of the triplet potential energy surface. In addition, because the HOMO–LUMO energy gaps can be controlled by adding various substituents, the corresponding adiabatic triplet energies can also be tuned. Compared with monometallic Pt(II) complexes, both the T₁A and T₁B excited states of bimetallic Pt(II) complexes exhibit the planar configuration and the energy differences between T₁A and T₁B are 12.42 and 12.56 kcal mol⁻¹, facilitating high phosphorescence quantum yields. Moreover, the large energy barrier of the temperature-dependent non-radiative decay process and small spin–orbit coupling matrix elements between T₁ and S₀ lead to a small non-radiative rate for the bimetallic Pt(II) complex. The results presented here are helpful in addressing the designed strategies as they show that the properties of the triplet potential energy surfaces for mono- and bimetallic Pt(II) complexes can be appropriately tuned.