A Cost-effective Phenothiazine-based Fluorescent Chemosensor for Selective Detection of Hydrazine and its Application To Real Water Samples.

Hydrazine is a highly toxic yet industrially indispensable compound extensively employed in aerospace, pharmaceutical, and polymer sectors. Its pronounced carcinogenicity and ecological persistence necessitate the development of sensitive and selective detection strategies, particularly for aqueous environments. Herein, we present PHENOZ, a cost-effective and structurally simple phenothiazine-based fluorescent probe functionalized with a dicyanovinyl moiety, capable of selectively detecting hydrazine with a prominent turn-on fluorescence response. PHENOZ was synthesized in only two steps from commercially available starting materials. The probe displayed no background fluorescence in the absence of hydrazine; however, a pronounced emission emerged upon hydrazine addition. This behavior is attributed to a nucleophilic attack of hydrazine on the electron-deficient dicyanovinyl group, which significantly alters the electronic structure of the molecule and activates the fluorescence pathway. A strong linear correlation between fluorescence intensity and hydrazine concentration was observed in the 0-40 µM range, with a detection limit of 0.22 µM (7.05 ppb) -well below the ACGIH toxicity threshold for aquatic systems. Selectivity experiments confirmed that PHENOZ exhibited no significant response toward potentially interfering species such as cyanide and primary amines. Furthermore, real sample analyses in tap, bottled, and lake water demonstrated recovery rates ranging from 94.7 to 111.1%, confirming the probe's potential for practical environmental monitoring. Taken together, these results establish PHENOZ as a highly selective, simple, and effective fluorescent chemosensor for hydrazine detection in aqueous media.