Metal Free C-H Functionalization of Pyrrolidine to Pyrrolinium-based Room Temperature Ionic Liquid Crystals

The development of ionic liquid crystals (ILCs) using pyrrolidinium cation has received considerable interest due to their higher electrochemical stability. However, high charge density associated with low charge distribution in the fully saturated pyrrolidine ring leads to the high melting temperature of the materials due to strong ionic interactions. Herein, the synthesis and evaluation of the structure–property relationship of a new class of pyrrolinium-based ionic liquid crystals has been reported. The metal-free direct C–H functionalization of pyrrolidine, followed by the N-alkylation of resulting pyrroline produced the pyrolinium moiety that serves as the unprecedented polar head of the mesogens. These ionic mesogens having a partially unsaturated pyrrolidine ring were found to stabilize numerous mesophases over a wide thermal range including room temperature.