A pH-sensitive ESIPT molecule with aggregation-induced emission and tunable solid-state fluorescence multicolor for anti-counterfeiting and food freshness detection

Achieving stimulus-responsive multicolor solid-state photoluminescence based on a single fluorescence compound has potential applications in anti-counterfeiting labels and visual detection. However, few such organic chromophores have these features and been used in this fields. In this study, multiple pH-sensitive sites were incorporated into a single molecule of succinimide substituted 2-(2'-hydroxyphenyl)Benzothiazole derivative (BTSA) that was Aggregation induced emission (AIE) and Excited state intramolecular proton transfer (ESIPT) active, exhibiting multilevel and highly secured anti-counterfeiting abilities. Under ammonia atmosphere, BTSA exhibits reversible switching between the green and blue fluorescence. By rationally manipulating two stimuli (acid and base), BTSA labels incredibly shows four different emission colors. The multicolor fluorescence changes are irreversible and evidently depend on the order of acid-base added. Together with smartphone that can quickly and accurately identify the multiple colors, BTSA affords a new covert fluorescent anti-counterfeiting technique with high security through the combination of reversible and irreversible fluorescence multicolor changes, as well as order and stimuli-dependent luminescent patterns. In addition, BTSA labels are successfully applied for real-time and visual monitoring the food freshness of pork and shrimp. The molecular design rationale presented here provide a new design strategy for the purposes of multicolor anti-counterfeiting and food freshness detection.