Nanosecond time-dependent fluorescence depolarization of diphenylhexatriene in dimyristoyllecithin vesicles and the determination of "microviscosity".

The nanosecond time dependence of the fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene in L-alpha-dimyristoyllecithin vesicles was determined at temperatures above and below the midpoint of the gel-liquid crystalline transition. In neither case could the decay of the total fluorescent emission or the decay of the emission anisotropy be described adequately in terms of single exponential decay laws. At the lower temperature, the emission anisotropy did not approach zero in the time window available for measurement, a finding which may indicate that the range over which rotation of the probe can freely occur is restricted. The results are discussed in relation to the concept of microviscosity of bilayer membranes.