Photoswitchable coordination cages

Stimuli-responsive behaviour is key to the design of smart materials, surfaces, nano-systems and effector molecules, allowing their application as switchable catalysts, molecular transporters, bioimaging probes or caged drugs. Supramolecular chemistry has embraced the widespread integration of photoswitches because of their precise spatiotemporal addressability and waste-free nature. In the vibrant area of discrete metal-mediated self-assembly, however, photoswitches are still rarely employed. Only recently has it been shown that embedding photoswitches into the organic backbones of coordination cages enables control of their host and material properties and thus unlocks the hitherto unexploited dynamic adaptivity of such systems. Here we discuss four cases where triggering ligand-integrated photoswitches leads to (1) control over disassembly/reassembly, (2) bi-stable switching between defined states, (3) interplay with thermal processes in metastable systems and (4) light-fuelled dissipative self-assembly. We highlight first clues concerning the relationship between fundamental photophysics and dynamic assembly equilibria and propose directions for future development. The self-assembly of stimuli-responsive building blocks yields functional nano-systems and smart materials. This Perspective discusses how the integration of photoswitches into discrete coordination cages enables control over their assembly, guest binding and systems behaviour. Four scenarios are drawn to highlight the relationship between the photoswitching and dynamic assembly equilibria.