Reversible ratiometric fluorescence probe for the detection of HClO/H2S based on excited state intramolecular proton transfer mechanism

The redox balance between HClO and H2S is essential for the physiological and pathological properties of organisms. Therefore, monitoring the redox process between HClO and H2S is of great significance. Shen et al. synthesised a reversible ratiometric fluorescence probe BT-Se based on excited state intramolecular proton transfer (ESIPT) reaction for the detection of HClO and H2S in previous experiments. When BT-Se detects HClO, it will be oxidised to a new substance which is named BT-SeO, and BT-SeO can be reduced to BT-Se by detecting H2S. BT-Se and BT-SeO emit different colours of fluorescence to realise detection. In this paper, the attribution of the fluorescence peak and the luminescence mechanism are studied. The bond parameters, infrared (IR) vibrational frequency, interaction region indicator (IRI) and the potential energy curve are analysed to demonstrate that the excited state is easier to conduct the ESIPT process. The combination of frontier molecular orbitals (FMOs) and hole-electron analysis reveals the charge excitation characteristics. This work suggests that the yellow and blue fluorescence observed in the experiment is emitted by the keto structures of BT-Se and BT-SeO, respectively. Our research will provide an important theoretical basis for the detection of photophysical phenomena in reversible ratiometric fluorescent probes.{GRAPHICAL ABSTRACT}