Photophysical properties of 1,2-dihydroxyanthraquinone in AOT reverse micelles

Abstract We report photophysical properties of 1,2-dihydroxyanthraquinone (alizarin) confined in methanol-in-oil reverse micelles by steady-state and time-resolved fluorescence spectroscopy. The formation of reverse micelles and confinement of alizarin molecules inside the reverse micelles were confirmed by Raman spectroscopy and fluorescence anisotropy measurements. The emission of alizarin centered at 585 nm showed 2.5–3.0 times increase in intensity in small reverse micelles, and the lifetime was also largely increased compared to those of bulk solution. We conclude that alizarin confined in the core of small reverse micelles has a strong interaction with the sulfonate head group of the surfactant Aerosol OT, and that the emission band at 585 nm originates from the alizarin with the proton partly deprotonated and trapped near the anionic surfactant head groups.