A Facile and Efficient Synthesis of BODIPY‐Based Fluorescent Probes for Selective Detection of Hydrazine

A facile and ratiometric BODIPY‐based fluorescent probe 4 was developed for the selective detection of hydrazine in solution phase. The BODIPY‐based fluorophores 3 and 4 were easily prepared in high yields from the L‐proline catalyzed reaction between α/β‐formyl BODIPY 1a/1b and 3‐cyanoacetylindole 2. Use of easily accessible substrates, benign solvent, catalytic amount of L‐proline and high yields are the advantageous features of the developed protocol. Prepared BODIPYs 3 (536 nm) and 4 (567 nm) showed bathochromic shifts (36‐67 nm) in UV‐Visible absorption maxima when compared to parent BODIPY (500 nm) in dichloromethane (DCM). The stable and economical BODIPY‐based probe 4 exhibited rapid response and remarkable selectivity towards hydrazine when compared to other commonly occurring analytes. At low concentration, the BODIPY probe 4 (10 μΜ) is non‐fluorescent, however, a significant enhancement in fluorescent (turn‐on) was observed with the increasing concentration of hydrazine solution (0‐100 μΜ). This change in fluorescent behaviour may be ascribed to intramolecular charge transfer (ICT) effect as supported by density functional theory (DFT) calculations. With a 4.3 μM detection limit, the BODIPY probe 4 was also found to be useful in detection of hydrazine in real environmental samples.