Light induced dynamics of a charge transfer probe in lipid vesicles

Distribution of a model twisted intramolecular charge transfer (TICT) probe in zwitterionic lipid vesicles of variable interior water pool sizes has been studied using steady state and time resolved fluorescence spectroscopy. This has been achieved by preparing unilamellar vesicles of different sizes, viz., small (SUVs), large (LUVs) and giant (GUVs) in water. The characteristic fluorophore shows an hypsochromic shift of 65 nm in its emission maximum in SUVs compared to bulk water, whereas in GUVs and LUVs this shift is similar to 58 nm. The decay profiles of the fluorescence probe are found to be comprised of three components in SUVs, LUVs and GUVs that could be due to the distribution of the molecule in the hydrophobic bilayer and the water molecules at the bulk and inner aqueous environments of the DPPC vesicles, respectively. This study indicates that TICT probes have specific distribution patterns in ground and excited states depending upon the size of the internal water pool of the lipid vesicles. Thus, the in vitro studies with these biomimicking lipid systems put forward the possible behaviour of such characteristic small molecules in biological cells.