Solvation dynamics in organized assemblies, 4-aminophthalimide in micelles

Solvation dynamics of 4-aminophthalimide (4-AP) has been studied in neutral (triton X-100, TX), cationic (cetyl trimethyl ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) micelles using picosecond time resolved Stokes shift. Above critical micellar concentration (CMC), for all the three micelles, 4-AP exhibits wavelength dependent fluorescence decays with a fast decay at the blue end and a slow decay accompanied by a distinct growth at the red end of the emission spectra. The time dependent Stokes shift indicates that the water molecules in the Stern layer of the micelles relax in ≈100 ps time scale which is markedly slower than the subpicosecond relaxation dynamics observed in ordinary bulk water