Rotational relaxation of the "microviscosity" probe diphenylhexatriene in paraffin oil and egg lecithin vesicles.

The rotational relaxation of the widely used "microviscosity" probe, 1,6-diphenyl-1,3,5-hexatriene, was examined by the technique of nanosecond time-resolved fluorescence depolarization. The decays of the emission anisotropy were determined at five temperatures in the range 3-31 degrees both in a reference paraffin oil and in sonicated egg lecithin vesicles. These decays were complex in both media. Marked qualitative as well as quantitative differences were observed in the rotational behavior of the probe in the complex bilayer medium as opposed to the homogeneous reference solvent. The results are discussed in relation to the structure of the hydrophobic bilayer membrane interior and the concept of its "microviscosity".