Amphiphiles as novel solvents for photochromics: stability and photophysical properties

The photochromic compound 2,6-bis(2-hydroxybenzilidene)cyclohexanone (PC) has been dissolved in some selected liquid amphiphiles: dibutyl, tributyl, bis-2-ethylhexyl, tris-2-ethylhexyl phosphate and bis-2-ethylhexyl amine. The aim was to explore its photophysical properties when embedded in the novel chemical environment provided by the amphiphilic solvents. UV-Vis spectra revealed different features depending on the solvent thus highlighting specific solvent-solute interactions and different chemical environments. All the alkylphosphate-based systems were found to be unstable; slow (days) changes in the absorption features due to the slow change in populations of the various species present in solution. Interestingly, the dissolution of PC into bis-2-ethylhexyl amine leads to stable solutions most probably due to the basic character of the solvent stabilising as major specie chalcone forms. Fluorescence spectra suggested the equilibrium between two species with different absorption and fluorescence properties.