Fluorous Tails and Anion Effects as Dual Drivers of Ionic Self-Assembly in Triazolium Ionic Liquid Crystals

Abstract

A series of perfluoroheptyl-substituted 1,2,4-triazolium ionic liquid crystals differing for the phenyl alkoxy substitution pattern (4-substituted, 3,4-substituted, 3,5-substituted) and the counter-ion (OTf^-, PF₆^-, NTf₂^-) have been investigated. Anion-exchange metathesis of three triazolium triflates gave five additional salts, all characterized by Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). Data reveal a consistent counter-ion effect: NTf₂^-derivatives exhibit lower melting and clearing temperatures than their PF₆^- analogues. Mesophase breadth and complexity are primarily dictated by cation structure, with 3,5-disubstituted derivatives showing narrow mesophase windows, while 4- and 3,4-substituted cations exhibit broader ranges and multiple transitions. POM observations corroborate smectic behavior in single-chain derivatives and layered or columnar organization in dialkyloxy analogues. Besides, dendritic growth in the 3,4-substituted PF₆^- salt suggests discotic aggregation. Overall, the combined effects of selective anion exchange and controlled peripheral substitution provide an effective strategy to tune mesophase type, thermal behavior and supramolecular organization in perfluoroalkyl triazolium ionic liquid crystals, offering transferable design principles for engineering fluorinated ILCs with targeted properties for structured electrolytes, ion-conductive materials and responsive soft devices.