Fluorescence probe properties of intramolecular charge transfer diphenylbutadienes in micelles and vesicles

Abstract

This paper reports absorption and fluorescence spectral studies of methyl 4-[(1E,3E)-4-phenylbuta-1,3-dienyl]benzoate (1), N,N-dimethyl-N-{4-[(1E,3E)-4-phenylbuta-1,3-dienyl]phenyl}amine (2), methyl 4-{(1E,3E)-4-[4-(dimethylamino)phenyl]buta-1,3-dienyl}benzoate (3) and 1-methyl-4-{(1E,3E)-4-[4-methoxyphenyl]buta-1,3-dienyl}benzoate (4) in homogeneous media of 1,4-dioxane and 1,4-dioxane-water binary mixtures, and in microheterogeneous media of cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton-X-100 micelles, and dipalmotoyl phosphatidylcholine (DPPC) vesicles. The binding site of the diene probes in micelles and vesicles has been determined and it has been found that while in micelles dienes occupy the polar interfacial regions, in vesicles the probes are located deep inside the hydrophobic bilayer. The binding of dienes to the vesicles is stronger than their binding to the micelles as indicated by the binding constant values. The fluorescence emission of the probe dienes in micelles is from a conformationally relaxed intramolecular charge transfer excited state. However, in vesicles, since the excited state conformational motions are restricted due to the rigidity of the alkyl chain, the dienes fluoresce from their planar locally excited states.