Lighting Up Nonemissive Azobenzene Derivatives by Pressure

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