Design, synthesis, and biological application of A–D–A-type boranil fluorescent dyes

Abstract

For the first time, three acceptor–donor–acceptor (A–D–A)-type boranil fluorescent dyes, CSU-BF-R (R = H, CH₃, and OCH₃), featuring phenothiazine as the donor, were designed and synthesized. CSU-BF-R exhibited remarkable photophysical characteristics, including large Stokes shifts (>150 nm), high fluorescence quantum yields (up to 40%), long-wavelength emissions, and strong red solid-state fluorescence. Moreover, these CSU-BF-R fluorescent dyes were demonstrated to function as highly selective and sensitive ratiometric fluorescent probes for detecting hypochlorous acid (HClO). The preliminary biological applications of CSU-BF-OCH₃ for sensing intracellular HClO in living cells and zebrafish were demonstrated. Therefore, CSU-BF-R possess the potential to further explore the physiological and pathological functions associated with HClO and provide valuable insights into the design of high-performance A–D–A-type fluorescent dyes.