FLUORESCENCE OF AMPHIPHILIC HEMICYANINE DYES WITHOUT FREE DOUBLE-BONDS

Amphiphilic hemicyanine dyes were obtained by coupling unpolar derivat ives of aniline and naphthylamine, respectively, to polar derivatives of pyridinium and isoquinolinium, respectively. These dyes have no fre e 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 solven ts 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 quant um yield of fluorescence by orders of magnitude. The effect is describ ed by an enhancement of nonradiative deactivation at an invariant radi ative decay. The enhancements of the Stokes shift and of the nonradiat ive 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 e xcited state. The properties of the dyes in amphiphilic assemblies are discussed in terms of their properties in bulk solvents.