Andrew Smith

Chemistry and Biochemistry

Faculty Advisor: Brandon Ashfeld

Annual 2020 Project: Preparation and Analysis of Photoswitchable Ionic Liquids

Cooling systems are extensively employed in key industrial procedures for a variety of applications. However, these systems are reliant upon energy-inefficient materials. To limit the environmental impact of coolants, new polymers and liquids have been considered for absorption-cooling systems as a function of their stimuli-responsive absorption with water. The temperatures at which these thermoresponsive materials separate into biphasic mixtures are called either upper- or lower-critical solution temperatures (UCST/LCST). Some ionic liquids (ILs) have displayed thermoresponsive properties. Furthermore, the structures of ILs have been demonstrated to greatly influence their UCST/LCST. Two ILs generated from fumarate and malate anions, trans and cis isomers of butenedioic acid, with tetrabutylphosphonium cation exhibited opposite UCST and LCST character respectively. It follows that control of the structural isomer composing the IL will impart significant control on its thermoresponsive properties. The azo functionality characterized by RN=NR’ has well established photoinduced cis/trans isomerization. It is envisioned that azo-containing ILs can be generated, such that the two interconvertible cis/trans isomers will exhibit opposite UCST/LCST properties. A variety of cationic frameworks to comprise these target ionic liquids are proposed possessing the azo functionality, such as imidazole, benzimidazole, and pyrazole rings. These nitrogen-containing heterocycles are considered because methods to install azo groups onto these heterocycles have
already been established, and many alkyl-substituted derivatives of these heterocycles have already been demonstrated to form ILs with a variety of anion partners. As azo-containing ILs are synthesized, their photoinduced isomerization and UCST/LCSTs in a variety of solvents will be measured. This data will help demonstrate the viability of these two-fold responsive systems as efficient and energy-inexpensive components of future cooling systems.