The Synthesis and Development of Photo-Actuating Materials using Organic Photochromes

The question that motivates my PhD research is how to convert light directly into actuation using organic photoswitches. To accomplish this goal, we must first move beyond traditional chromophores to find photoswitches whose optoelectronic properties are optimized for a given scenario. Among these, donor–acceptor Stenhouse adducts (DASAs), are especially promising due to their negative photochromism, tunable absorption profile, and large volume change. To incorporate DASAs into photo-actuating materials a better understanding of the photophysical properties is crucial, as well as understanding the concentration dependence. In this effort, we explored the concentration dependence and effect of ionic character on DASAs. The effects of solution-state dielectric and intermolecular interactions on the degree of charge separation of the open form provides a route to understanding the switching properties and concentration dependence of DASAs. Second, developing a high efficiency photoswitch is not sufficient to make a viable photo-actuating material. Once such a molecule is incorporated into a solid matrix, numerous factors can affect its ability to react, including polymer matrix and photochrome density. We need robust, scalable, and efficient methods to access a range of DASA-based materials and actuator designs to evaluate actuation performance. We demonstrate a synthetic platform to chemically conjugate DASA to a load-bearing poly(hexyl methacrylate) (PHMA) matrix via Diels−Alder click chemistry that enables access to DASA-based materials on scale. By leveraging the ease of fabrication of a bilayer design, we developed a tunable, visible light-responsive bilayer actuator driven by the photothermal properties of DASAs. Further, we investigate the influence of the host matrix on the photothermally-driven actuation performance of DASA- based polymers. We designed polymeric materials with varying photochrome incorporation and investigated the relationships between material composition and the resulting physical, mechanical, and photoswitching properties. Finally, we report and compare the light-induced property changes in the glass transition temperature and elastic modulus between the materials comprising of the open or closed form of DASAs. This work establishes the foundational relationships between mechanical and photoswitching properties and is critical to advancing the use of DASA-based materials