Dual Fluorescence of p -Dimethylaminobenzoic Acid in Cetyltrimethylammonium Bromide (CTAB)/1-Heptanol/Water Reverse Micelle

Abstract

Dual fluorescence of p-dimethylaminobenzoic acid (DMABOA), typical of excited-state twisted intramolecular charge transfer (TICT), in the cetyltrimethylammonium (CTAB)/1-heptanol/H₂O reverse micelle has been monitored as a function of a number of factors such as the water pool size, the bulk concentrations of DMABOA and CTAB, and the pH and [KF]/[KBr] ratio in the water pool. Two fluorescence parameters, i.e., the wavelength of the TICT emission band and the intensity ratio of the TICT band to the LE (locally excited state) band, I_a/I_b, are employed to measure the effects of these factors. The position of the DMABOA molecule in the reverse micelle is ascertained to be among the hydrocarbon chains close to the water pool with its (CH₃) ₂N group towards the bulk 1-heptanol while the carboxylic group interacts with the polar head of the surfactant electrostatically. The TICT of DMABOA at this position is shown to be similar to that in an organic solvent, and the reverse micelle exerts a restriction on the TICT of DMABOA. It seems that the water molecules in the water pool do not penetrate into the hydrocarbon region of the reverse micelle.