Effect of substituent position on aggregation-induced emission, customized self-assembly, and amine detection of donor-acceptor isomers: Implication for meat spoilage monitoring

Abstract We synthesized a class of positional isomers by attaching electron donor and acceptor units in different sites of a conjugated core. These isomers exhibit both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) effects, which are proved by adequate spectroscopic analysis. Their structure-property relationships were systematically studied. We found that relocation of the D/A units would have remarkable impact on the intermolecular dipole-dipole interaction, further controlling the shape and color of the self-assembled architectures. With D/A units shifting to different sites, four types of the structures appear sequentially, including quadrate microsheets, microrods, nanofilaments and nanowires. Furthermore, the A unit (benzoic acid moiety) of the AIE isomers is easy to adsorb amines, leading to changes in both emission wavelength and intensity. Then a portable sensor is prepared on solid support based on the self-assembled architecture of HMBA-4, which has been proved to be the most sensitive to amines. It affords fast spectral responses as well as a low detection limit of 186 Pa (vapour pressure). The sensing mechanism was revealed by density functional theory (DFT) calculation, which indicates that the spectral responses stem from the weakened ICT effect. The sensor is able to detect amine vapours generated by meat, and thus succeeds in detecting the spoiled pork samples, offering high potential for meat spoilage monitoring in real-world applications.