The fluorescence response of a structurally modified 4-aminophthalimide derivative covalently attached to a fatty acid in homogeneous and micellar environments

The photophysical properties of 11-(4-N,N-dimethylaminophthalimido)undecano ic acid (DAPL), a surfactant covalently labeled with a fluorophore, in homo geneous and micellar media are reported. The remarkable sensitivity of the fluorescence properties of DAPL to the polarity of the media is attributed to the existence of a low-lying nonfluorescent twisted intramolecular charg e transfer (TICT) state. DAPL is found two be an excellent fluorescence sen sor for following the micellar aggregation process. Although DAPL shows enh anced binding with the micelles, the quenching experiments and the fluoresc ence spectral and intensity data clearly indicate that the fluorescing moie ty does not penetrate into the nonpolar core region of the micelles even th ough the fluorophore is covalently attached to the nonpolar end group of th e fatty acid. It is unambiguously established from the fluorescence data th at both of the terminal groups of DAPL are located in the interfacial regio n of the micelles by folding of the long polymethylene chain.