Excited-state intramolecular proton transfer (ESIPT) and charge transfer (CT) fluorescence probe for model membranes

Motivated by the burgeoning interest in designing and characterizing fluorescence probes with superior spectroscopic properties for exploring the structural and dynamic aspects of biological systems, we have investigated the photophysical behaviour of a synthetic flavonol, namely 4'-N,N-dimethylamino-3-hydroxyflavone (DMA3HF) in model membranes consisting of small unilamellar liposomes of the phospholipids DPPC and DMPC. The DMA3HF fluorophore is remarkable in the fact that it combines both excited-state proton transfer (PT) and charge transfer (CT) fluorescence emissions in a single molecular system. The nature and relevant parameters of the dual emission profiles, fluorescence excitation spectra, along with steady-state fluorescence anisotropy (I) and red edge excitation shift (REES) data have been used to probe the local environments of DMA3HF molecules in liposomes. Furthermore, r versus temperature (T) profiles are shown to provide estimates of thermotropic gel to liquid-crystalline state phase transition temperatures of the phospholipids, in excellent agreement with the existing literature data. (C) 1999 Elsevier Science B.V. All rights reserved.