Fluorescent molecular probes .2. The synthesis, spectral properties and use of fluorescent solvatochromic Dapoxyl(TM) dyes

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 E-T (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.