Stimuli-responsive room-temperature phosphorescence regulation based on molecular packing mode conversion

There are still limit reports to realize stimuli-responsive room-temperature phosphorescence (RTP) through molecular packing mode conversion of organic small compounds. Moreover, utilizing photoirradiation to regulate RTP emission behavior without chemical structure change, as a new kind strategy of functional optical material preparation, remains an interesting and challenging topic. Herein, we designed a new class of benzil derivatives: 1,2-bis (4-alkoxyphenyl) ethane-1,2-dione (BP-X). Among three molecules, 1,2-bis(4-(2-(2-(2-methoxyethoxy) ethoxy) ethoxy) phenyl) ethane-1,2-dione (BP-1) showed tangible and reversible phosphorescence conversion between cyan and green RTP under various external stimuli (mechanical force, thermal annealing and solvent fume). Besides, when irradiated with ultraviolet light, the molecular motion enhanced, leading to the packing mode of grinding state BP-1 reordering, which synchronously triggered its photo stimuli-responsiveness from green colour RTP emission back to cyan without destroying chemical structure. Both experimental and theoretical studies indicated that the multilevel stimuli-responsive phenomenon was attributed to molecular packing mode conversion and the alternation of molecular conformation of excited state. Such unique multilevel stimuli-responsive property supplies a facile strategy to enrich the advanced smart RTP materials.