High Contrast Electrochromism in Organic Materials

Over the course of this program, we have developed both molecular and polymeric electrochromic materials with a special focus on understanding how the structure of conjugated systems can be altered to control radical cation and dication formation, and how this leads to optical transitions that manifest as a color change. Combining computational efforts, via collaboration with Prof. Aime Tomlinson at the University of North Georgia, with the Reynolds group synthetic capabilities and characterization expertise has allowed us to deepen the level of understanding of cathodically coloring polymer electrochromes and break new ground in understanding the electronic and optical properties of novel anodically coloring electrochromes. Overall, we establish a more thorough fundamental understanding of redox behavior of conjugated systems, as we begin to see a growing interest in applying conjugated systems for mixed transport applications. In the area of polymer electrochromes, we highlight our development of a high-gap orange-to-clear polymer, demonstrating stability of thousands of switches, as well as the ability to be blended with other colors to attain black-to-clear electrochromic inks. With respect to fundamental work in the field of organic electronics, we deepened the understanding of how subtle structure property relationships specifically side-chain tuning impacts the performance of conjugated polymers in electrochemical and mixed-transport systems, demonstrating sub-second switching of electrochromic polymers in aqueous electrolyte for tens of thousands of switches. Additionally, we elucidated electrochemically charged states of conjugated polymers, proposing a model wherein formation of a charge-transfer state precedes formation of radical cations. Finally, we have developed a family of anodically coloring electrochromes, showing how straightforward synthetic handles can tune the optical absorbance of the oxidized state in predictable ways.