Portable and rapid hydrazine monitoring by a large Stokes shift probe with smartphone-assisted quantification: Its...

A novel phenanthroimidazole-based donor-π-acceptor fluorescent probe incorporating benzothiazole and arylidene nitrile units was designed for the rapid and selective detection of hydrazine (N₂H₄). The probe exhibits strong orange fluorescence arising from an intramolecular charge transfer (ICT) process, which is switched to blue emission upon reaction with N₂H₄ due to disruption of the π-conjugated system. The sensing platform shows excellent selectivity toward N₂H₄ over metal ions, anions, amines, and biologically relevant species, along with a rapid response (∼120 s) and a low detection limit of 81 nM. A large Stokes shift (∼188 nm) effectively minimizes background interference. Mechanistic studies confirm that nucleophilic addition of N₂H₄ to the arylidene nitrile unit modulates the ICT process, leading to pronounced optical changes. The probe demonstrates good biocompatibility (cell viability >85% at 200 μM) and enables vapor-phase detection via probe-coated TLC kits with a clear orange-to-blue fluorescence response under UV light. Practical applicability is further demonstrated in soil, plant, and food samples, while smartphone-assisted analysis yields result consistent with the ninhydrin method. Overall, the developed system provides a simple, portable, and reliable platform for environmental monitoring of hydrazine.