Lighting\nUp Nonemissive Azobenzene Derivatives by\nPressure

Pressure-induced\nemission (PIE) is a compelling phenomenon that\ncan activate luminescence within nonemissive materials. However, PIE\nin nonemissive organic materials has never been achieved. Herein,\nwe present the first observation of PIE in an organic system, specifically\nwithin nonemissive azobenzene derivatives. The emission of 1,2-bis(4-(anthracen-9-yl)phenyl)diazene\nwas activated at 0.52 GPa, primarily driven by local excitation promotion\ninduced by molecular conformational changes. Complete photoisomerization\nsuppression of the molecule was observed at 1.5 GPa, concurrently\naccelerating the emission enhancement to 3.53 GPa. Differing from\nthe key role of isomerization inhibition in conventional perception,\nour findings demonstrate that the excited-state constituent is the\ndecisive factor for emission activation, providing a potentially universal\napproach for high-efficiency azobenzene emission. Additionally, PIE\nwas replicated in the analogue 1,2-bis(4-(9<i>H</i>-carbazol-9-yl)phenyl)diazene,\nconfirming the general applicability of our findings. This work marks\na significant breakthrough within the PIE paradigm and paves the novel\nhigh-pressure route for crystalline-state photoisomerization investigation.