Rationally Designed Fluorescence . OH Probe with High Sensitivity and Selectivity for Monitoring the Generation of . OH in Iron Autoxidation without Addition of H 2 O 2

The first sensitive fluorescence . OH probe ( 1 ) that is capable of monitoring the generation of trace . OH in iron autoxidation is presented. The probe 1 was designed by utilizing both the unique aromatic hydroxylation and the electrophilicity of . OH, and prepared by incorporating a strong electron‐donating methoxy group into a cyanine fluorochrome to enhance the trapping ability for . OH. Reaction of 1 with . OH leads to a larger π‐conjugation formation and near‐infrared fluorescence off–on response. The capability of probe 1 has been demonstrated by imaging . OH generated in living cells under iron autoxidation as well as various stimuli, which reveals that the basal level of . OH in RAW 264.7 cells is lower than that in HeLa cells. The superior analytical performance of probe 1 makes it useful for detecting trace . OH in some critical physiological and pathological processes associated with iron autoxidation.