Unraveling the defect-induced photoluminescence of a donor-acceptor AIE luminogen

Abstract This work reveals the synthesis and photophysical properties of a donor-acceptor (D-A) aggregation-induced emission (AIE) compound, (E)-(4-((4-(diethylamino)-2-hydroxybenzylidene)amino)phenyl) (phenyl)methanone (DHPM), and further discloses its unique behavior, i.e., defect-induced photoluminescence (DIPL). The crystalline state of DHPM is non-emissive, whereas it exhibits high emission in the crystal defect points. Semiquantitative analysis demonstrates that mechanical force down to mN level would cause defect points on the crystal surface, further activating the DIPL, which manifests as a turn-on mechanoresponsive luminescence at the macro level. The crystallographic data and quantum chemical calculation suggest that DHPM molecules aggregate into D-A coupling π-dimers in the crystalline state to the disadvantage of luminescence; while the external mechanical stimuli such as pressing and grinding would destroy intermolecular weak interactions to disassemble the dimers, inducing much higher photoluminescence relative to the untreated crystal. In an application example, a mechanoresponsive film was prepared using DHPM, capable of storing handwriting patterns and binary data.