Circular Dichroism Photoswitching with a Twist: Axially Chiral Hemiindigo.

Chiroptical properties play a crucial role not only for molecular structures and their functions but also for advanced applications such as molecular sensing, absolute asymmetric synthesis, or information processing and storage. Manipulating chiroptical characteristics in a predictable and reversible fashion by outside means is therefore a highly desirable option to enhance the functions and reporting abilities of a molecular system. Herein, we present axially chiral hemiindigo photoswitches showing unusual chiroptical changes upon visible-light irradiation. While absorption remains high throughout the spectrum, the corresponding ECD signals can be reversibly erased and reestablished in an ON/OFF manner upon photoswitching. Taken together with exceptionally high thermal bistabilities, leading to half-lives of the metastable states up to 3400 years at ambient temperature, and high photoswitching quantum yields these chiral hemiindigos offer unique possibilities for, e.g., smart molecule, photonic materials, or sensing applications.