SPECTROSCOPIC STUDIES OF COUMARIN IN MICELLES

Steady-state and time-resolved emission spectroscopic techniques have been employed to characterize the coumarin species and identify which species is solubilized in the hydrocarbon core micelles of triton X-100 (neutral), hexadecyltrimethyl ammonium bromide (cationic) and dodecyl lithium sulfate (anionic) solutions under physiological conditions at 77 K. The emission and absorption spectra for the following species of coumarin-monomer, hydrogen-bonded complex, molecular aggregation and strong hydrophobic aggregates-were recorded in methylcyclohexane (MCH), ethanol, buffers and aqueous solutions. The fluorescence and phosphorescence emissions of monomer in MCH at 77 K are assigned as resulting from (1)(pi,pi*)(1) and (3)(pi,pi*)(1) states, respectively, originated from the ethylenic bond and carbonyl of the pyrone ring. Molecular orbital calculations using the Hydrogenic Atoms in Molecule, version 3, method were carried out to help interpretation of the spectroscopic results. The photophysical properties from each species are used to probe which species penetrates in the hydrophobic region of micelles. It was found that a fifth species of coumarin assigned as the ''action species'' is solubilized into the interior of micelles. These observations could lend some insight into the mechanism of transporting coumarins across the membrane.