Construction and Application of a New Polarity‐Sensitive Fluorescent Probe Based on the Excited‐State Intramolecular Proton Transfer Mechanism

A new excited‐state intramolecular proton transfer based near‐infrared emission and polarity‐sensitive fluorescent probe (E)‐3‐((E)‐2‐chloro‐3‐((E)‐2‐(3‐ethyl‐1,1‐dimethyl‐1H‐benzo[e]indol‐2(3H)‐ylidene)ethylidene)cyclohex‐1‐en‐1‐yl)‐1‐(2‐hydroxyphenyl)prop‐2‐en‐1‐one (M‐NA) was developed. This probe consisted of benzomerocyanine unit and o‐hydroxyacetophenone unit. In high‐polar solvent, M‐NA displayed higher fluorescence and longer emission wavelength. Theoretical calculations data showed that M‐NA had larger emission oscillator strength and lower non‐radiative decay in high polarity media, corresponding with the fluorescence character. Further experiments verified that M‐NA possessed excellent selectivity and stability, and could further quantify the accurate polarity as well as the water content of binary mixed solvent. We have developed a new polarity‐sensitive fluorescent probe based on excited‐state intramolecular proton transfer mechanism, displaying weak fluorescence in low‐polarity solvent and intense fluorescence in high‐polarity solvent.