Thioether-functionalized picolinium ionic liquids: synthesis, physical properties and computational studies

A series of ionic liquids containing 3- and 4-picolinium cations appended to thioether side chain moieties was constructed via the thiol–ene “click” reaction. Their structure–property relationships were comprehensively investigated by studying the temperature transition region (melting points and glass transition temperatures) and heat capacity and the experimental results were fully supported by theoretical studies. The synthesized ionic liquids are melted below 20.2 °C. Also, the impact of varying chain length, type of cations (picolinium vs. imidazolium) and the position of methyl group on the ring on their thermal and thermophysical properties were explored. According to the collected data, the glass transition temperature values of the picolinium-based ionic liquids with odd-number chains is lower than the even-number ones, which shows that the even-number moieties have more organized structures. And the miscibility of selected ionic liquids in water (polar) and heptane (nonpolar) solvents were quantified.