Abstract
Molecular photoswitches that reversibly isomerize when exposed to external stimuli, such as light, heat, and current have been used for diverse applications in drug delivery, sensing, controlling hydrophilicity of surface, actuation, and many other fields. The wide range of applications is achieved primarily due to their significant changes in physical and optical properties upon isomerization. However, the isomerization dynamics of these compounds are typically studied in dilute solution or dispersion in polymer matrices, which is a relatively unhindered environment for conformational isomerizations. Understanding the molecular switching behavior in a sterically-hindered and close-packed environment, such as in a condensed phase or at an interface with 2D-materials, is essential for developing diverse solid-state applications. I studied the impact of light, heat, and current on the isomerization dynamics of spiropyran, arylazopyrazole, and azobenzene derivatives in condensed phases and on 2D-materials. In these materials, I demonstrated that external stimuli can effectively control their phase, heat storage/release cycles, and intermolecular interactions by manipulating the ratio of isomers. In this thesis work, I focused on elucidating the molecular design principles for controlling their optical and thermal properties, as well as demonstrating their effective application in photon energy conversion, thermal energy storage, and optical memory. In addition, I conducted fundamental investigations on the photo-induced conformational changes of such photoswitches, in collaboration with electron microscopists, to gain atomic-level understanding of the process. This imaging technique was further utilized for tracking molecular interactions with the surface of a 2D material as well. This thesis will hopefully provide a holistic view of molecular photoswitches’ properties and utilities in various environments.