Subtle changes in molecular conformation can significantly influence the frontier orbital distribution and energy level arrangement. By the construction of molecules with distinct stable conformations, dual-emission is achieved through their differentiated triplet energy levels. However, a long-standing challenge in this field lies in balancing the relationships among these conformational states, overcoming rapid energy exchange, and mutual quenching between them. Herein, we designed two crystal materials with room-temperature phosphorescence (RTP) dual emission properties in a single-component system through substituent engineering: 1,2-bis(4-methylphenyl)ethanedione (p-BJ) and 1,2-bis(4-methoxyphenyl)ethanedione (p-BOX). These crystals exhibit different substitution sites on their benzene rings, effectively modulating intermolecular steric hindrance. As steric hindrance diminishes, intramolecular interactions weaken, enabling the excited-state conformations of p-BJ and p-BOX crystals to relax into more planar structures under an external force. This conformational transformation ultimately induces the RTP dual emission in p-BJ and p-BOX. This work provides a new approach for achieving single-component dual emission by regulating the excited-state conformation.
Zhang et al. (Tue,) studied this question.