Solvent polarity scale on the fluorescence spectra of a dansyl monomer copolymerizable in aqueous media

A copolymerizable fluorescent monomer N-[2-[[[5-(N,N-dimethylamino)-1-naphthalenyl]sulfonyl]-amino]ethyl]-2-propenamide (DANSAEP) was synthesized, which exhibits dual fluorescence due to the twisted intramolecular charge transfer in the excited state. The emission maximum λem shifts from 463.3 nm in n-hexane to 530.0 nm in water, showing solvent polarity dependence. The relations between λem and the conventional solvent polarity parameters ET(30) or Z are linear, dividing solvents into protic and aprotic groups. Kamletʹs linear solvation energy relationship gives a good description for λem as a solvent polarity scale. The increment of dipole moment Δμ at the excited state was estimated as 5.09 D with the solvatochromic analysis.