Mechanically Interlocked Indigo Photoswitches

Photoswitches provide the opportunity to remotely and precisely control matter on the nanoscopic scale. For many materials and biological applications, photoswitches with long wavelength response are essential; however, few switches offer inherent response to red/near infra-red light. Previous works have described the use of intermolecular interactions as a method to redshift the activation wavelength of photoswitches and to improve thermal half-life. However, these systems are limited in their application due to the inherent bimolecularity of this strategy preventing its use in dilute or complex environments. Herein, we describe the use of topologically constrained supramolecular interactions to improve the switching properties of an indigo photoswitch within a [2]-rotaxane. This enabled photoswitching with 730 nm light, as well as a 100-fold increase in thermal half-life and double the population of the metastable state under constant irradiation. This surpasses previous attempts at using supramolecular interactions to increase the thermal half-life by >10-fold. This novel strategy towards the redshifting and fine-tuning of these molecular photoswitches has implications for the design of molecular machines and applied switching technologies. We anticipate that our insights into the design of such molecules will unlock new applications for mechanically interlocked molecules.