Dimer-Embedded Model Reveals Aggregation-Induced Phosphorescence in Pt(II) Complexes: A QM/MM Study

Rigid planar Pt(II) complexes have emerged as promising phosphorescent emitters because of their high luminescence efficiency and diverse structural tunability. In this work, we carried out a comprehensive theoretical investigation of Pt(II) complexes coordinated with homo- and heteroleptic ligands. The analysis of monomers revealed that the rigid pyridine group in heteroleptic complexes 4-6 could effectively elevate the T1 energy and enhance the spin-orbit coupling effect. However, these planar Pt(II) complexes still need an aggregation effect to achieve a high photoluminescence quantum yield (PLQY). Then, the solid-state aggregated dimers of complexes 1, 2, and 5 were simulated using a two-layer ONIOM model. We found that the ligand structure and R substituent collaboratively regulated the molecular stacking. The closely arranged packing mode of dimer 5 in the solid was beneficial to enhancing MLCT and restraining excited-state structural deformation, leading to a high PLQY of 98.6%.