Design and synthesis of photoactive ionic liquids.

Two ionic liquids with photoisomerizable p-hydroxycinnamic acid moieties were synthesized and characterized by X-ray crystallography and DSC, and their photochemistry was studied in solution and neat conditions. Irradiation at absorption maxima led to trans-cis photoisomerization and resulted in significant reduction of melting temperatures of the ionic liquids. X-ray structures of both compounds show an intricate network of supramolecular interactions before irradiation. Physical and chemical transformations are completely reversible upon irradiation at lower wavelengths of ionic liquid solutions in acetonitrile.