The effect of micelle-water interface electric field on the intramolecularcharge transfer within ionic micelle - Dual fluorescence of sodium p-dialkylaminobenzoates in cetyltrimethylammonium micelles

Photoinduced intramolecular charge transfer (CT) of sodium p-(dimethylamino )- and p-(diethylamino) benzoates (SDMAB and SDEAB) in cetyltrimethylammoni um bromide and chloride (CTAB and CTAC) micellar solutions was investigated by the CT typical dual fluorescence, in order to identify the effect of mi celle-water interface electric field on the CT process occurring within ion ic micelle. The CT fluorescence in CTAB and CTAC micelles was blue shifted and enhanced compared to those in pure water. The intensity ratio of the CT fluorescence to the LE fluorescence, I-a/I-b, of either SDMAB or SDEAB was found to be higher in CTAC micelle than in CTAB micelle, while these fluor ophores experience the same polarity in both micelle environments. It was p roposed that the higher I-a/I-b ratio in CTAC micelle was due to stronger e lectric field at CTAC micelle-water interface. This was supported by experi ments on the dual fluorescence of SDEAB and SDMAB of different CT-state dip ole moment in CTAB micelles of varying micelle-water interface electric fie ld. It was demonstrated that the electric field at the ionic micelle-water interface indeed affected the CT process occurring within micelle that the CT process is promoted and the CT emission is enhanced at higher electric f ield. Ionic micelle was shown capable of acting as the electric field 'medi ator' for chemo- and biosensing based on the dependence of the CT dual fluo rescence on electric field. (C) 1999 Elsevier Science S.A. All rights reser ved.