The molecule of nile red (NR) contains a big aromatic ring and a carbonyl oxygen (electron acceptor) that can hydrogen-bond with a water molecule, resulting in high sensitivity to the microenvironments of the micellar palisade layer in which NR is solubilized. In the aqueous micellar solution of dodecyltrimethylammonium bromide (C12TABr), the dual fluorescence of NR appeared and the maximum emission wave lengths were at 578 and 630 nm, respectively. The dissociation degree of the counterion from sodium dodecyl sulfate (SDS) micelle was found to be larger than that of C12TABr. This increased both the microenvironment polarity around NR and the hydrated water for the heads resulting in the enhancement of the hydrogen bonds with water. As a result, the fluorescent intensity of SDS solution was reduced compared with that of C12TABr but the TICT state was effectively promoted to form, which produced the high population of the TICT state over 98% and thus apparent single fluorescent peak at 634 nm. By the high sensitivity of NR to microenvironment, the information about uncompleted structure of the micelles formed initially was also obtained, which indicates that NR can be used as the probe to determine the aggregates formed by the amphiphilies with strong intermolecular synergism.

Key words: TICT probe, nile red, environment-sensitivity, the information about the micellar palisade layer