Boronate-Based Fluorescence Probes for the Detection of Hydrogen Peroxide

In this work, we synthesized a series of boronate ester fluorescence probes (E)-4,4,5,5-tetramethyl-2-(4-styrylphenyl)-1,3,2-dioxaborolane (STBPin), (E)-N,N-dimethyl-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styryl)aniline (DSTBPin), (E)-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styryl)benzonitrile (CSTBPin), (E)-2-(4-(4-methoxystyryl)phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (MSTBPin), (E)-N,N-dimethyl-4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)styryl)naphthalen-1-amine (NDSTBPin), and N,N-dimethyl-4-(2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)oxazol-5-yl)aniline (DAPOX-BPin) for the detection of hydrogen peroxide (H₂O₂). DSTBPin and MSTBPin displayed an "Off-On" fluorescence response towards H₂O₂, owing to the loss of the intramolecular charge transfer (ICT) excited state. Whereas, CSTBPin displayed a decrease in fluorescence intensity in the presence of H₂O₂ owing to the introduction of an ICT excited state. STBPin, on the other hand, produced a small fluorescence decrease, indicating the importance of an electron-withdrawing or electron-donating group in these systems. Unfortunately, the longer wavelength probe, NDSTBPin, displayed a decrease in fluorescence intensity. Oxazole-based probe DAPOX-BPin produced a "turn-on" response. Regrettably, DAPOX-BPin required large concentrations of H₂O₂ (>3 mm) to produce noticeable changes in fluorescence intensity and, therefore, no change in fluorescence was observed in the cell imaging experiments.