Unusually high quenching rates of two coumarins C-152 and C-152A inside niosome

9 Photoinduced electron transfer (ET) reactions between coumarin dyes and N, N10 dimethylaniline have been investigated inside niosome, a nonionic innocuous 11 Polyethylene glycol (PEG)-based surfactant assemblies using steady state and time12 resolved fluorescence measurements. The location of coumarin dyes has been 13 reported inside bilayer headgroup region of niosome and it was verified by 14 determination of high distribution coefficient of all the dyes inside niosome compared 15 to bulk water. Fluorescence anisotropy parameters of the dyes inside niosome are also 16 in good correlation with the above inference about their location. Bimolecular 17 diffusion guided rates inside niosome was determined by comparing the 18 microviscosities inside niosome and in acetonitrile and butanol solutions and it was 19 found that diffusion of donor and acceptor is much slower than the ET rates implying 20 insignificant role of reactant diffusion in ET reaction inside niosome. We have 21 obtained Marcus inversion region in our restricted media, which shows maxima at 22 lower exergonicity. Such behavior has been demonstrated by the presence of 23 nonequilibrium solvent excited state using two dimensional ET (2DET) theory. 24 Unusually high quenching rates of two coumarins C-152 and C-152A inside niosome 25 were explained by the presence of stable non-fluorescent twisted intramolecular 26 charge transfer (TICT) state along with emissive intramolecular charge transfer (ICT) 27 state. Moreover, intermolecular hydrogen bonding between carbonyl oxygen of these 28 two dyes with water in their non-emissive and emissive charge transfer states also play 29 a key role for their dynamical exchange to each other. 1 30 Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics This journal is © The Owner Societies 2012