Non-reversible solvatochromism in N-methyl-2-pyrrolidone/toluene mixed solutions of fullerene C60

Non-reversible changes in the UV–Vis spectra (solvatochromism) of C60 fullerene in the binary solvent N-methyl-2-pyrrolidone/toluene are observed when varying the mixture composition. The solvatochromism strongly depends on the order of the mixture preparation. We attribute the effect to a great difference in the polarity of the liquid components, which determines different solvent–solute interaction with respect to the formation of charge-transfer complexes and, thus, provides conditions for selective solvation. The effect is also dependent on the temporal changes in the complexes C60–N-methyl-2-pyrrolidone and C60 cluster formation.