Fluorescent Molecular Probes II. The Synthesis, Spectral Properties and Use of Fluorescent Solvatochromic Dapoxyl Dyes

Abstract— 2,5‐Diphenyloxazoles that embody a dimethylamino group at position 4 of the 5‐phenyl ring and a sulfonyl group at position 4 of the 2‐phenyl ring were prepared as new fluorescent solvatochromic dyes. In these molecules, there is a “push‐pull” electron transfer system from the 5‐phenyl moiety to the 2‐phenyl ring. These compounds show strong solvent‐dependent fluorescence that is well correlated with the empirical solvent polarity parameter ET (30). The solvent polarity dependence suggests that the fluorescence arises from an intramolecular charge transfer. The fluorescence‐environment dependence, long emission wavelength, large extinction coefficients, high fluorescence quantum yields and large Stokes shift of the fluorophores can be used to develop ultrasensitive fluorescent molecular probes to study a variety of biological events and processes.