Fluorescent molecules, whose spectra or quantum yields are sensitive to their surrounding environments, are valuable in the study of heterogeneous media, organized media and biological media, and many fluorescent solvatochromic dyes have been developed for these applications. However, the existing fluorescent solvatochromic dyes either have short absorption and emission wavelengths, low extinction coefficients, low quantum yields or small Stokes shift. We have recently developed solvatochromic DapoxylTM dyes, whose fluorescence maximum shifts to longer wavelengths, and fluorescence quantum yield decreases with increasing solvent polarity. In these molecules, there is a 'push-pull' electron transfer system from the 5-phenyl moiety to the 2-phenyl ring. The compounds show strong solvent-dependent fluorescence that is well correlated with the empirical solvent polarity parameter ET(30). These dyes have also shown long emission wavelengths, high extinction coefficients, high quantum yields and large Stokes shifts. Their biological applications will also be discussed.