A BODIPY‐Based Cascade Sensing Approach for Hydrazine and Formaldehyde Using Colorimetric and Fluorescent Signals

In this study, we developed a BODIPY‐based sensor 10‐(4‐bromophenyl)‐5,5‐difluoro‐5H‐4l4,5l4‐dipyrrolo[1,2‐c:2′,1′‐f][1,3,2]diazaborinine (BDY), for the selective and sensitive detection of hydrazine across solid, liquid and gas phases. BDY interacts with hydrazine via a nucleophilic addition reaction at the BODIPY core, leading to fluorescence quenching and a visible colour change. The sensing mechanism was elucidated through 1 H NMR titration experiments, confirming the disruption of the conjugated π electron system. BDY demonstrated a remarkable limit of detection (LOD) of 0.029 µM (0.9 ppb), for hydrazine and demonstrated practical applicability through its sucessfull detection in cigarette smoke. Furthermore, the BDY‐Hz complex was utilized as a secondary probe for formaldehyde (FA) sensing, enabling a cascade detection approach. The sensor exhibited an ON‐OFF‐ON fluorescence switching mechanism, where interaction with FA restored the original optical properties of BDY. FA detection was successfully achieved in solid and liquid phases with a LOD of 0.3 µM calculated in liquid phase. Additionally, a starch‐polyvinyl alcohol‐based hydrogel matrix was employed for on‐site detection of hydrazine in cigarette and formaldehyde in a fish sample. This work introduces a novel strategy for dual‐analyte sensing, utilizing the BODIPY core as both the signaling and binding site, with potential applications in environmental and industrial monitoring.