Rapid photoluminescence “turn-on” sensing of tertiary amines and opioids via dual-emissive ground and excited charge-transfer states

The recognition and differentiation of organic amines are essential for applications in drug analysis, food spoilage, biomedical assays, and clinical diagnostics. Existing luminescence-based recognition methods for amines largely rely on fluorescence quenching. Here, we present a photoluminescence “turn-on” approach for rapidly distinguishing different organic amines based on their unique excited-state and ground-state interactions with naphthalimide, where the quantum yield and emission color are influenced by amine substituent groups and molecular flexibility. Specifically, primary and secondary amines and other common lone-pair donors, including alcohols, ethers, thiols, thioethers, and phosphines, exhibited no visual photoluminescence changes. 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. Additionally, the “turn-on” process is influenced not only by the substituent group but also by distinct ground- and excited-state dynamics observed in time-resolved spectroscopy. This approach enables the rapid and qualitative recognition of opioids, such as heroin, fentanyl, and metonitazene, offering a simpler and faster alternative to existing methods like the Marquis reagent kit, with potential applications in on-site testing and real-time monitoring.