Pyrene aided dual mode fluorophore sensor for trace hydrazine detection in real environmental samples: Design,...

A sustainable approach to hydrazine detection is presented via the design and synthesis of eight novel fluorophores through Claisen-Schmidt condensation, catalysed by KOH and pyrrolidine under mild conditions. While KOH (2-3 h; 73-79%) afforded speedy catalyst, pyrrolidine (4-6 h; 83-89%) enabled efficient catalyst access to a diverse set of polynuclear aromatic scaffolds. The resulting fluorophores were fully characterized by NMR and HRMS, and their photophysical behaviours were systematically investigated in various solvents. A standout candidate, based on 1-Pyrenecarboxaldehyde, demonstrated exceptional promise as a dual-mode (colorimetric and fluorometric) sensor for hydrazine. The detection mechanism involves a hydrazine-induced cyclization event that disrupts π-conjugation and intramolecular charge transfer, triggering rapid optical changes visible to the naked eye. The sensor exhibited ultra-low detection limits (0.33 μM with 5 μM 3d, i.e. (E)-1,3-di(pyren-1-yl) prop-2-en-1-one), high selectivity, and robust performance against a wide range of interfering species and pH (4-10) variations. Real-world applicability was confirmed through successful detection of trace hydrazine (1-5 μM) in environmental water, soil, and food samples. Furthermore, a low-cost, paper-based sensing platform was developed, enabling portable, equipment-free detection. This work showcases a practical and sustainable fluorophore design strategy for environmental toxin monitoring and paves the way for future field-deployable, green sensing technologies.