Computational investigation of graphene quantum dot and tridentate Au(iii) complex composites

Abstract

The radiative and nonradiative decay processes of a series of Au(III) complexes were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) to explore the influence of graphene quantum dots (GQDs) as ligands on the emission properties and phosphorescence quantum yields. The absorption curves, emission wavelengths, hole–electron analysis, spin density analysis, and spin–orbit coupling (SOC) matrix elements were utilized for a better understanding of the radiation decay rate constants and photoinactivation mechanisms. Our study reveals that adding GQDs as ligands into Au(III) complexes has little impact on their structural stability. Moreover, we found that the fusion of GQDs helps in stabilizing the ground and excited states of Au(III) metal complexes. Importantly, our findings suggest that GQDs have a beneficial effect on the phosphorescence emission process, for instance, suppressing the nonradiative leap and enhancing the phosphorescence quantum yield. Furthermore, the results of the hole–electron analysis show that the addition of GQDs largely reduces the MC leap of Au1, favorably increasing the probability of radiative decay. Spin density analysis also indicates the suppression of ³MLCT characteristics in Au2 and Au3 complexes with GQD ligands. Interestingly, our calculations also reveal that the energy barrier of Au2 is higher than that of Au1 in the ³ES → ³MC transition in the photoinactivation pathway, leading to a higher phosphorescence quantum yield. Overall, we have demonstrated the significant potential of GQDs as stabilizers in our tridentate Au(III) complexes and provided important molecular insights for efficient phosphorescence emission.