*3.3.3 Hydrogen peroxide (H2O2)*

Zhang et al. have synthesized a new NIR and colorimetric fluorescent molecular probe, **DCBP7**, by covalently attaching dicyanomethylene-4*H*-benzopyran and phenylboronic acid for rapid detection of H2O2 [67]. The boronic acid functional group is attached primarily to have NIR fluorescence off–on switching. The sensing of H2O2 was successfully demonstrated by UV–visible absorption and fluorescence measurements. **DCBP7** exhibit a structured absorption band at 450 nm, and its solution appears pale yellow in color. However, with gradual addition of H2O2 (>20 equiv.), apparently, the absorption at 450 nm decreases, and a new absorption band starts evolving at 560 nm. Due to the large redshift (110 nm) of the absorption, the color of the solution (yellow) changed to purple, and colorimetric detection of H2O2 is visible even to the naked eye. The fluorescence measurements were also carried out to confirm the H2O2 sensing behavior of the probe molecule. The free probe molecule is non-fluorescent primarily because of phenylboronic group. However, after adding H2O2, the boronic acid group gets cleaved and generate a phenolate ion which is evident from the new fluorescent emission band at 670 nm. The Stokes shift (110 nm) of the phenolate band in the NIR region has been exploited further for detecting H2O2 and imaging live cells. Unlike the most conventional fluorescent probes, the developed **DCBP7** has been shown to have unique advantages such as deeper tissue penetration ability, lower background autofluorescence, and less damage to biological samples which ultimately allowed to in vivo studies of live cells.
