Fluorination effect on the solubility of C60 in a bis(trifluoromethylsulfonyl)imide based ionic liquid

Abstract

Highly fluorinated fullerenes with a chemical composition of C60F48 have been prepared and characterized. Their solubility of the new nanomaterials in the ionic liquid (IL) has been compared with raw fullerenes C60. Fluorination may appear as a convenient method to enhance the solubility of carbonaceous nanomaterials in a fluorinated based anion IL. Indeed, the ability of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BmIm][NTf2]), to solubilize C60 and C60F48 was investigated using optical microscopy and UV–vis spectroscopy. While C60 has very poor solubility in this IL (below 0.07 mmol/L), the solubility increases at least eightfold, i.e. more than 1.0 mg/mL (or 0.61 mmol/L) for C60F48 samples. The presence of fluorine atoms on fullerene seems to enhance the stability of the solvated molecules in IL thanks to the limitation of the aggregation of C60F48 in [BmIm][NTf2]. This improvement of the solubility could be explained by the beneficial effect of the fluorination that induces a decrease of the π-π interaction between carbonaceous solutes as the carbon hybridization changes from sp2 to sp3 through the formation of C-F covalent bonds and thus enhances the interaction between the solvent and the solute. Fluorination appears as an efficient approach to limit the use of volatile organic compounds usually used as co-solvent to enhance the dispersion mechanism.