Rapid Fluorochromic Sensing of Tertiary Amines and Opioids via Dual-Emissive Ground and Excited Charge-Transfer States

The recognition and differentiation of organic amines are crucial for applications in drug analysis, food spoilage, biomedical assays, and clinical diagnostics. Existing luminescence-based recognition methods for amines predominantly rely on fluorescence quenching, limiting the scope of sensitive and selective detection. Here, we present a fluorochromic approach for rapidly distinguishing different organic amines based on their unique excited-state and ground-state interactions with a naphthalimide derivative under ultraviolet light. Our findings reveal that the photoluminescence quantum yield and emission color are significantly influenced by the substituent group and the molecular flexibility of the amine. Specifically, primary amines, together with other common lone-pair donors, such as alcohol, ether, thiol, thioether, and phosphine, did not exhibit photoluminescence changes, while secondary amines exhibited only weak emission. For tertiary amines, however, bright green photoluminescence activation was rapidly produced for molecules containing at least one methyl group; red-shifted yellow emission was observed for ones with bulkier side groups other than methyl; and for conformationally locked bicycloamines, no emission was observed. In addition, this fluorochromic process of the naphthalimide derivative not only depends on tertiary amine substituent groups but also shows distinctly different ground- and excited-state photoluminescence dynamics in time-resolved spectroscopy. Based on these differences, a qualitative method is developed for visual recognition of natural and synthetic opioids, including heroin, fentanyl, and metonitazene, which is more facile and rapid compared to current methods such as the Marquis reagent kit, and could facilitate onsite testing, real-time monitoring, and streamlined workflows in both laboratory and field settings.