UC Santa Barbara

The detection of light is vital to monitoring environmental UV radiation, employing fluorescence in biomedicine and gene sequencing, and in operating visible light camera technologies. In optoelectronics, light-responsive ionic polymers offer the opportunity to implement solvent-processable active layers into devices such as photodetectors, memory, and circuits. Among the choices of charged polymers, polymeric ionic liquids (PIL) have attracted attention for their thermal stability and synthetically tunable ionic and mechanical properties. The incorporation of small molecules known as organic photoswitches, which undergo reversible light-induced isomerizations, can render PILs light-responsive. In the first half of this dissertation, I will discuss the synthesis and application of the first azobenzene-based polymeric ionic liquid as a light-responsive layer for an organic photodetector. The azobenzene polymeric ionic liquid (Azo-PIL) was synthesized with orthogonal solubility to a non-polar organic semiconducting polymer, which enables a simple solvent-based deposition process for fabricating an organic photodetector. The PIL-based photodetector quickly responds to light with multiwavelength-sensing capabilities due to an interfacial charge-transfer mechanism. In the second half of this dissertation, I will describe the development of a photoresponsive PIL designed with the ability to change mechanical properties concomitant with trans–cis isomerization. We designed and carried out the multi-step synthesis of an acrylate-based PIL, poly(azo-stat-IL). Upon the deposition of poly(azo-stat-IL) with lithium bis(trifluoromethanesulfonyl)imide (10 wt%) on an interdigitated electrode, UV irradiation induces a 50% decrease in conductivity. I will describe the progress on this project with regards to the design principles of poly(azo-stat-IL), characterization of the isomerization via UV–Visible Spectroscopy and Differential Scanning Calorimetry, and our working hypothesis for the mechanism responsible for the reversible change in ionic conductivity.