Synthesis of 3-hydroxyflavone fluorescent probes and study of their fluorescence properties

Direct measurement of dipole potential in biological membranes has been impossible and 3-hydroxyflavones (3HFs) have allowed detection of changes in dipole potential in biological systems. In the present study, sixteen derivatives of 3HF with aliphatic hydrocarbon chains of different lengths at 4′-position and 6-position were synthesized. The basic fluorescence properties of 3HFs are maintained in all the probes in terms of strong blue shift in maximum fluorescence emission wavelength and >100 fold increase in quantum yield in organic solvents and in dioleoylphosphatidylcholine (DOPC) small unilamellar vesicles (SUV) in comparison to in aqueous Hepes buffer (15 mmol/L, pH 7.4). More importantly, the ability of the new compounds to report dipole potential changes in biological systems are also maintained, since all the new probes showed spectrum properties that are similar to yet different from that of F4N1, which potentially may allow more sensitive measurement of the dipole potential change in membranes.