Aurélie Lafuma

Molecular design of hybrid organic-inorganic nanocomposites with emission and photochromic properties

Hybrids organic-inorganic nanocomposites are obtained though the hydrolysis and condensation of diethoxymethylsilane and methyltriethoxysilane alkoxides with or without the use of Lewis acids such as Zr(OPrn)4 or Al(etac)(OBus)2 precursors. These materials which present both reductive and hydrophobic behavior are performant host matrices for rare-earth cations and for photochromic dyes such as from spirooxazines (SO), diarylethene derivatives (DE) and furylfulgides (FF). We report the room temperature synthesis of new Eu2+ doped hybrid materials together with their absorption and emission properties. The photochromic properties of the different dyes (SO, DE, FF) in these hybrid solid matrices are also described. Very fast kinetics of coloration and thermal fading (0.2 s-1) are reproducibly evaluated for spiroxazines, while for the first time, quantum yields of the coloration process of diarylethene derivatives and furylfulfydes embedded in solid sol-gel derived matrices are measured.

Probing the micellar solubilisation and inter-micellar exchange of polyphenols using the DPPH free radical

Encapsulation of polyphenols can be used for improving their stability and targeting. We present here a spectrophotometric method to probe the micellar solubilisation and inter-micellar exchange of polyphenols using the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) free radical as a visible probe. Our method relies on the partitioning of DPPH· into micelles, on the reduction of DPPH· by polyphenols, and on the change in absorbance of DPPH· when reduced/oxidised. Hence, an absorbance drop at 528 nm gives evidence of the co-localisation of polyphenols and DPPH· in micelles. Using catechin and sodium dodecyl sulfate (SDS) as model molecules, we have shown that the reduction stoichiometry increases up to the critical micelle concentration (CMC) of SDS, where it reaches a plateau: this is due to the solubilisation of catechin in pre-micellar aggregates and then in micelles. The initial rate of reduction increases with increasing SDS concentration up to the CMC and then decreases due to a dilution effect.