Ultrafast Dynamics of Curcumin Inside Room-Temperature Ionic Liquid (RTIL)-Containing Microemulsions: A Triple-FRET Approach to White-Light Production

The polyphenolic medicinal pigment curcumin exhibits ultrafast solvation dynamics and excited-state intramolecular proton transfer (ESIPT), which contribute to its antioxidant behavior. These ultrafast dynamics are sensitive to the rigidity of the surrounding medium. Here, we investigated the excited-state dynamics of curcumin within two sets of ionic liquid (IL)-in-oil microemulsions of varying sizes, containing two distinct room-temperature ionic liquids (RTILs), with Triton X-100 (TX-100) as the surfactant and cyclohexane as the nonpolar medium. Anisotropy measurements reveal that small-sized microemulsions are less rigid than larger ones. Notably, ESIPT dynamics are slower in larger, more rigid microemulsions than in smaller, less rigid ones. Furthermore, white light (WL) emission was achieved in reverse micelles and microemulsions using the three-component fluorescence resonance energy transfer (Triple-FRET) technique, employing the hydrophobic dye 1,6-diphenyl-1,3,5-hexatriene (DPH) as the donor, curcumin as the intermediary donor, and merocyanine-540 (MC540) as the acceptor. Optimized dye concentrations within specific self-assembled structures enabled efficient WL generation through the triple-FRET mechanism.