Heteroaryl bis chalcone based photoluminescent on-off chemosensors for real-time hydrazine detection: design, synthesis and DFT studies

Hydrazine is a highly toxic and environmentally hazardous compound widely used in aerospace, agriculture, and industrial processes, necessitating the development of sensitive and reliable detection systems. In the present study, an eco-friendly strategy for hydrazine detection is reported through the synthesis of novel heteroaryl-based bis-chalcone chemosensors via Claisen Schmidt condensation under mild conditions. The reaction employs KOH and pyrrolidine as catalysts in three different solvents (i.e. Toluene, THF, Ethanol), where KOH enables a shorter reaction time (2 h, 77% yield), whereas pyrrolidine provides higher efficiency (5 h, 94% yield) in ethanol. The synthesised chemosensors were comprehensively characterized using various spectroscopic techniques, and their photo physical properties were systematically investigated. These prepared probes have demonstrated dual detection capability for hydrazine through both colorimetric and fluorometric responses. Sensing mechanism proven by mass analysis involves hydrazine-induced cyclization that disrupts π-conjugation and intramolecular charge transfer (ICT), resulting in significant optical changes observable by the naked eye. Density functional theory (DFT) calculations were also performed to gain insight into the electronic structure and ICT characteristics. This study confirm hydrazine induces an irreversible cyclization to a 1H-pyrazole product, disrupting ICT and resulting in rapid fluorescence quenching. The probes showed excellent analytical performance with low limits of detection (LoD 3a at 1.1 and 3b at 1.3 μM) and limits of quantification (LoQ 3a at 3.4 and 3b at 4.1 μM) at fixed probe concentration of 5 μM. Furthermore, the sensors displayed high selectivity toward hydrazine in the presence of potential interfering species and maintained stable performance across a wide pH range (5–10). The practical applicability of the sensing platform was validated by detecting trace hydrazine (0–5 μM) in environmental samples including water, soil, and food matrices with excellent recovery in real time (T 90 60 Sec.). Additionally, a low-cost paper-based sensing platform was developed, enabling portable and equipment-free hydrazine detection at ppm level with different temperatures and relative humidity.