Substituent and Hydrostatic Pressure Regulation of Triplet Exciton Dynamics in Organic Room-Temperature Phosphorescent Crystals

In contrast, MM-MPT achieves more favorable triplet utilization by rigidifying the excited-state structure through strong intermolecular confinement, resulting in suppressed non-radiative losses. Furthermore, hydrostatic compression of MM-HPT continuously reduces excited-state structural relaxation and enlarges the T₁-S₀ energy gap, producing a pronounced phosphorescence hypsochromic shift from 528 to 471 nm.

Pressure-induced orbital reconstruction and weakened excitonic coupling further reveal the microscopic origin of the emission evolution. These findings establish a molecular-level design principle that efficient RTP emission requires balancing triplet generation, radiative transition, and structural relaxation suppression rather than simply enhancing spin–orbit coupling, providing new insights into the rational design of stimulus-responsive organic phosphorescent materials.