FLUORESCENCE OF AMPHIPHILIC HEMICYANINE DYES WITHOUT FREE DOUBLE-BONDS

Amphiphilic hemicyanine dyes were obtained by coupling unpolar derivatives of aniline and naphthylamine, respectively, to polar derivatives of pyridinium and isoquinolinium, respectively. These dyes have no free double bond that is prone to photoisomerization. They are effective voltage-sensitive probes in biomembranes. The dyes were characterized by their spectra of absorption and by the spectra, the quantum yields, and the lifetimes of fluorescence. (i) An enhanced polarity of solvents shifts the absorption to the blue and the fluorescence to the red. The solvatochromism is described by an enhancement of the Stokes shift at an invariant 00 energy. (ii) An enhanced polarity lowers the quantum yield of fluorescence by orders of magnitude. The effect is described by an enhancement of nonradiative deactivation at an invariant radiative decay. The enhancements of the Stokes shift and of the nonradiative decay are assigned to two types of intramolecular charge-transfer that couple to polar solvents. The first one is induced by electronic excitation. The second one is induced by intramolecular twist in the excited state. The properties of the dyes in amphiphilic assemblies are discussed in terms of their properties in bulk solvents.