title: Photophysics and photodynamics of 1'-hydroxy-2'-acetonaphthone (HAN) in micelles and nonionic surfactants forming vesicles: a comparative study of different microenvironments of surfactant assemblies.
abstract: The effect of different microenvironments inside various biomimicking supramolecular assemblies of ionic (SDS/CTAB) and nonionic (TX100) micelles and nonionic surfactants (Tween-80/PEG-6000) forming vesicles (niosome) on the photophysical and rotational dynamical properties of 1'-hydroxy-2'-acetonaphthone (HAN) have been studied using steady-state and time-resolved fluorescence spectroscopy. Enhanced fluorescence intensity with a significant blue shift and longer emission lifetime of the caged tautomers of HAN indicate modulation of photophysics of HAN upon encapsulation in both micellar assemblies and the niosome system. The binding constant and free energy change for the complexation of HAN with micelles and niosome demonstrate a comparative study on the binding efficiency of the different assemblies depending on the nature of microenvironments toward HAN. The enhancement in the steady-state anisotropy in niosome solutions compared with that in pure aqueous solution indicates that HAN is located inside the motionally restricted bilayer region of niosome. The fluorescence quenching experiment further reveals the probable location of HAN in micelles and niosome. In TX100 micelles, the obtained lifetime values are 417 ps and 1.63 ns for the caged tautomers, whereas in the comparatively more rigid and confined environment provided by niosome those values are 444 ps and 2.5 ns. The rotational relaxation time constants for the caged tautomers in niosome are also found to be higher than those in micelles. The observed difference in binding ability of the different assemblies is due to the difference in the extent of water penetration and different extent of rigidity around the fluorophore.
authors: Department of Chemistry, Indian Institute of Technology, Kharagpur, West Bengal 721302, India.
authors: Sarthak
authors: S
authors: Mandal
authors: Vishal Govind
authors: VG
authors: Rao
authors: Chiranjib
authors: C
authors: Ghatak
authors: Rajib
authors: R
authors: Pramanik
authors: Souravi
authors: S
authors: Sarkar
authors: Nilmoni
authors: N
authors: Sarkar