Photophysical studies on a fluorescence probe labelled fatty acid: Chain folding in a micellar environment

The photophysical properties of 4-aminophthalimide fluorophore labelled detergent, 11-(4-aminophthalimido)undecanoic acid, that is capable of acting as a probe for microheterogeneous media, has been studied in homogeneous and micellar environments. From the surfactant-induced changes in fluorescence intensities, the binding constants and the critical micellar concentrations of three different micelles have been determined. The location of the fluorophore in the micellar environment is determined on the basis of the spectral shift, changes in fluorescence intensity and lifetime in micellar media and fluorescence quenching behaviour towards selected ionic quenchers. It is shown that despite its covalent linking with the non-polar tail of the surfactant chain, the fluorescing moiety localises itself in the interfacial region of the micelle by folding up of the long alkane chain.