Nanomolar fluorescent detection of hydrazine via condensation induced aggregation and enhanced emission

Hydrazine (N₂H₄) is a widely used industrial chemical with significant environmental and health hazards, necessitating the development of efficient detection methods. Fluorescent probes offer a promising alternative to conventional analytical techniques due to their high sensitivity, cost-effectiveness, and operational simplicity. In this study, we report two commercially available aldehydic probes, HN (2-hydroxynaphthaldehyde) and DAS (4-(N, N-diethylamino)salicylaldehyde), for selective and sensitive hydrazine detection through a condensation-driven fluorescence turn-on mechanism. On condensation with hydrazine, these probes exhibited distinct aggregation-induced emission enhancement (AIEE) behaviors, enabling their application in different solvent environments. The photophysical properties of the condensation products have been extensively evaluated theoretically from DFT. HN demonstrated a sharp fluorescence enhancement in the presence of hydrazine due to aggregation induced emission enhancement of the condensation product HDBN in 2:8 v/v (THF: water). DAS , on the other hand, showed a similar fluorescence enhancement, albeit in organic-rich environment of 8:2 v/v (DMSO: water). An exceptionally low LOD of 12 nM and 36 nM is calculated for the sensors HN and DAS respectively, making them suitable for hydrazine monitoring in water systems. Based on the promising photophysical characteristics, a strip paper test was developed for visual detection of hydrazine in both solution and vapour phases. This study elucidates the importance of solubility and aggregation properties in optimizing sensor performance.