Synthesis and photophysical properties of side-chain chlorinated benzo[a]phenoxazinium chlorides

Abstract

Novel water-soluble benzo[a]phenoxazinium chlorides mono- or dissubstituted with 3-chloropropyl groups at the amine of position 9, and also at the hydroxyl function at position 2, were synthesised. These compounds possessing one, two or three chlorinated terminals displayed fluorescence emission in ethanol and water in the range 644-666 nm and 649-676 nm, respectively, with fluorescence quantum yields from 0.26 to 0.38. It was found that this type of molecules is involved in acid-base equilibrium and tautomerization with localized positive charge. Ab-initio ground and excited state DFT calculations were made for the various possible tautomers of a model compound. Preliminary studies of the photophysical behaviour of these compounds in AOT/cyclohexane reverse micelles with low water content (ωo=[Water]/[AOT]≤5) showed that they interact strongly with the headgroups in the interface feeling the presence of an increased amount of water. At very low ωo values, AOT molecules promote the tautomerization process allowing it to follow both in absorption and emission spectra.