Photosensitive Trans-Cis Isomerization of Cyanine Dye Stains-All by Biological Surfactants

Both the biological surfactants, sodium cholate and sodium deoxycholate red shift the λ_max of the fluorescence emission beyond some characteristic surfactant/dye mole ratio (S/D 20.0 for cholate and 2.00 for deoxycholate). The two surfactants induce sharp blue shifted metachromasia in this dye initiated at these two characteristic S/D values. The red shift of the fluoescence peak has been interpreted in terms of trans→cis photoisomerization of the dye bound to the surfactants. The monomeric dye, free or bound to the surfactants, does not undergo this photoisomerization. In contrast, the nonionic surfactant Triton X-100 does not induce photosplitting, but induces single emission peak at 615 nm. The photophysics of this surfactant-induced changes in emission has been discussed. The structure of the all-trans and mono-cis isomer of Stains-all derived from computer modelling, has been shown.