Absorption and emission studies of solubilisation in micelles. Part 3.—Fluorescence polarization of solubilisates in cationic micelles

Abstract

Measurements of fluorescence depolarisation are reported for perylene in dodecyl- and hexadecyl-trimethylammonium bromide micelles. The activation energies for perylene rotation, respectively 36 and 35 kJ mol^–1 in spherical micelles, are within experimental error identical to the activation energies for pyrene excimer formation. The implications of this are discussed in terms of two-dimensional diffusion, and, within this model, coefficients of lateral diffusion calculated.

The energy transfer contribution to fluorescence depolarisation is measured for perylene in hexadecyl-trimethylammonium bromide; from this the average separation r of perylene molecules in micelles containing two perylene molecules is calculated as 2.2 ⩽r < 4.0 nm, a result which confirms the absence of solubilisate aggregation for these systems. Depolarisation results on perylene in high concentration dodecyl-trimethylammonium bromide solutions indicate that as cationic micelles become rod-like the microviscosity activation energy decreases significantly.

Results are also reported on the fluorescence depolarisation of β-(9-n-hexadecyl-10-anthryl) acetic acid in hexadecyl-trimethylammonium bromide micelles.