A red-emitting fluorescent probe with a large Stokes shift for selective detection of hypochlorous acid

An optical probe (3) with a donor-pi-acceptor (D-pi-A) structure for the detection of hypochlorous acid (HClO) was synthesized by a one-step reaction. It employed a barbituric acid derivative as the electron acceptor and 4-(dimethylamino)cinnamaldehyde as the electron donor. The probe exhibited high sensitivity and selectivity for the detection of HClO, rapidly responding with distinct colorimetric and fluorescent "on-off" signals (about 15 s). The probe displayed a linear relationship between fluorescence intensity and HClO concentration, with a low detection limit (LOD) of 14 nmol center dot L-1, which made it suitable for quantitative HClO detection. Moreover, the probe exhibited red light emission (628 nm) with a significant Stokes shift (158 nm) and good photostability, which provided advantages for its application in cell imaging. The proposed reaction mechanism, which was deduced from high-resolution mass spectrometry data, involved electrophilic addition and oxidative cleavage of the C=C bond by ClO-, which led to the disruption of the probe's D-pi-A structure. Consequently, this effectively halted the intramolecular charge transfer (ICT) process of the probe. MTT cytotoxicity assays demonstrated minimal toxicity of the probe following 12, 24, and 48 h of incubation with HepG2 cells. The probe was successfully applied to living cell imaging and enabled the detection of HClO via fluorescence quenching within the living cellular milieu.