Fluorescence properties of surface-active styrylcyanine molecular rotors

This paper reports on some photophysical properties of a newly synthesized styrylcyanine chromogen 1 of electron donor—acceptor type, namely 1-cetyl-4-[4′-( N- N-dimethylamino)-styryl]-pyridinium bromide. The fluorescence properties of this self-organized surfactant chromogen were studied in non-homogeneous media. Its fluorescence shows a sensitivity to environmental factors which could be exploited profitably as a fluorescence probe in various systems of industrial and biological importance. A remarkable enhancement in its fluorescence efficiency was observed in a rigid ethanol matrix at 77 K and in micellar solutions. Moreover, a considerable edge-excitation red shift was observed in a PMMA matrix at room temperature similar to that found in glassy ethanol. The results provide some information on the free-volume distribution in a PMMA matrix. The changes noted can be rationalized, relative to the short-chain model compound 2 in terms of an enhanced sensitivity of the highly organized and tightly packed molecules 1 to viscocity—torsional reactions between solute and solvent