Azobenzene-Oxindole Photochromic Dyads

Abstract

Manipulation of molecular geometry using photoresponsive units is a powerful tool in supramolecular chemistry, smart materials, and photopharmacology. Current synthetic chemistry offers many responsive molecules that perform such a task. However, the incorporation of various photoresponsive units in a single molecule to achieve several geometrical changes remains scarce, particularly when they are in close proximity. The development of such systems is limited by challenges arising from selectively addressing the photoresponsive moieties and the analysis of complex mixtures. Here, we overcome these challenges by constructing a novel hetero-photochromic azobenzene-oxindole dyad (AOD). Both chromophores can be addressed and quantified in solution by in situ NMR irradiation analysis. Additionally, this method allows us to unravel the intricate photokinetic relationships between the two chromophores, leading to the observation of an unprecedented molecular motion: an azobenzene E → Z → E isomerization at a single wavelength due to the oxindole influence. By functionalizing the azobenzene ring, we showed that the responsiveness of the system is maintained in seven distinct AODs. Overall, the photochromic dyad offers dramatic geometrical changes over its four isomers, making it a useful tool for further applications in which such behavior is desired, such as host-guest systems, responsive materials, photopharmacology, and molecular machines.