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

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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.

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