Design of Dipolar Push–Pull Fluorophores Based on Furanone–Nitrile Acceptors for Ratiometric Hydrogen Sulfide Sensing

Hydrogen sulfide (H2S) is a toxic and biologically relevant gas, necessitating sensitive and interference-resistant detection methods for environmental monitoring. Here, we develop a donor–acceptor molecular platform incorporating a polarized conjugated double bond bridge and demonstrate its application, using YG2 as the representative probe, as a dual-peak ratiometric UV–Vis sensor for H2S. UV–Vis spectroscopy, supported by 1H NMR analysis, indicates HS--induced interaction with the conjugated linkage, leading to disruption of π-conjugation, suppression the intramolecular charge-transfer (ICT) band at 409 nm, and enhancing the locally excited (LE) band at 279 nm. The ratiometric parameter log(Abs279/Abs409) affords a linear response over the concentration range of 1.0 × 10−6–1.0 × 10−4 M with a detection limit of 8.3 × 10−7 M, providing approximately an order-of-magnitude improvement in analytical sensitivity compared with single-wavelength methods, and the reaction reaches completion within ~10 s. YG2 exhibits excellent selectivity toward H2S over common anions and enables accurate quantification in real water samples, with recoveries of 95.43–105.86% and relative standard deviations (RSDs) of 0.56–9.58%. These results suggest that YG2 is a rapid, self-calibrating, and spectroscopically interpretable ratiometric probe suitable for reliable H2S detection in complex aqueous environments.