SOLVENT RELAXATION BEHAVIOR OF N-ANTHROYLOXY FATTY-ACIDS IN PC-VESICLES AND PARAFFIN OIL - A TIME-RESOLVED EMISSION-SPECTRA STUDY

Time-resolved fluorescence measurements were performed for a set of n- anthroyloxy fatty acids (n-AS; n = 2, 3, 6, 9, 12, 16) in both solvent and vesicle systems. The Stokes' shifts and the mean relaxation times calculated from the time-resolved emission spectra (TRES) are shown t o be strongly dependent on the position of the fluorophore in small un ilamellar vesicles (SUV) composed of phosphatidylcholine (PC)I while t hey are essentially independent of the fluorophore position in isotrop ic paraffin oil. The concept of an intramolecular relaxation process w hich had been suggested to explain the wavelength dependence of the em ission behaviour of the n-AS dyes in viscous solvents is supported by semiempirical calculations showing that a more planar conformation is favoured in the excited compared to the ground state. However, in orde r to explain the results in vesicle systems, the concept of intramolec ular relaxation is not sufficient. Rather, we show that intermolecular solvent relaxation processes play the dominant role for the wavelengt h dependent emission behaviour in polar, viscous environments.