Brightening Blue Photoluminescence in Non‐Emission Phthalic Anhydride by Pressure‐Driven Molecular Reassembly

Abstract Constructing organic materials with rigid‐planar molecules provides a unique platform for obtaining efficient photoluminescence (PL) by suppressing vibrational relaxation and extending the π ‐conjugation. However, the presence of H‐aggregates/excimers resulting from interactions between π electrons and lone pairs during crystalization leads to aggregation‐caused quenching. Here, an alternative pressure‐treatment approach is presented for regulating molecular assembly to brighten rigid‐planar phthalic anhydride (PA) crystals with initial non‐emission. The pressure‐treated PA crystals exhibit significant blue‐light emission under ambient conditions, accompanied by a PL quantum yield of up to 15.7% and Commission International de I'Eclairage color coordinates of (0.20, 0.19). Detailed experiments and calculations reveal that pressure‐treated hydrogen bonds promote the planar rotation among PA molecules, which facilitates intermolecular π ‐conjugation. This extended π ‐conjugation alters the exciton relaxation channel, thereby triggering blue‐light emission based on charge transfer (CT) states. Remarkably, the obtained PA crystals also exhibit linear piezochromism (4.56 nm GPa −1 ) as a result of the structural sensitivity of the CT process. This work demonstrates the feasibility of regulating molecular assembly to achieve solid‐state emission in rigid‐planar molecules with initial non‐emission and opens up a new platform toward stimuli‐responsive crystalline materials.