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

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.