Polar Perturbations of Dipolar Interactions in Azole-Based Poly(ionic liquids)

Abstract

Azole-based polymeric ionic liquids (PILs) containing imidazolium (Im) p(Im-TFSI) and triazolium (Tr) p(Tr-TFSI) ring cations naturalized by bis(trifluoromethane sulfonyl)imide (TFSI) anions were synthesized to elucidate the origin of dipolar–ionic interactions and their role in conductivity and mechanical properties. Spectroscopic analysis of p(Im-TFSI) and p(Tr-TFSI) PILs revealed that the presence of polar H₂O alters ionic and dipolar interactions, resulting in distinct ring-dependent hydration effects. In p(Tr-TFSI), more stable cation–anion–H₂O entities result from stronger electrostatic surface potentials (∼2 kcal/mol), where distinct separation of positive and negative electrostatic potentials in Tr-TFSI cation–anion pairs facilitates the formation of localized clusters inducing dipole–dipole interactions. In the presence of H₂O, ionic mobility is enhanced by solvating cation–anion pairs at the expense of weaker van der Waals interactions. The content of H₂O near Tr rings is higher, but there is restricted ionic mobility due to stronger polar forces that are formed at the expense of diminished induced dipole–dipole interactions. In contrast, in Im-based polymers, H₂O molecule associations with cation–anion pairs are weaker, and enhanced ionic mobility is reflected in increased conductivity values by a factor of 2. Both Im and Tr rings also facilitate distinct parallel resistor–capacitor (RC) responses with constant phase element (CPE) combinations; upon exposure to H₂O, the parallel RC circuits undergo configuration by an additional in-series connected R-CPE element.