Key-enabled molecular rotation modulates intramolecular hydrogen bonding toward a turn-on trace-level N2H4 sensor†

Hydrazine (N₂H₄) is a highly toxic and versatile chemical raw material that has been widely used in industrial production and agricultural applications, but it has also caused environmental pollution. In this research, a fluorescent probe SDG-2 was designed and synthesized for hydrazine detection through esterification functionalization of pyridinium acylion. Hydrazine induces the hydrolysis of the ester group in SDG-2 to a hydroxyl group, thereby creating an intramolecular hydrogen bond donor that results in fluorescence enhancement, characteristic of sensitive N₂H₄ monitoring. Analytical results demonstrate that SDG-2 achieves an exceptional detection limit of 0.43 μM with a linear response spanning 20–250 μM. The probe exhibits remarkable selectivity and resistance to interference from competing analytes, accompanied by recovery rates ranging from 92.40 to 106.27% in practical sample analysis. This work establishes a robust molecular platform with significant potential for environmental hydrazine assessment, featuring both operational convenience and analytical reliability. The mechanistic insights into IMHB-mediated sensing provide valuable guidelines for developing advanced fluorogenic probes for environmental chemistry applications.