Manipulation and control at the molecular level is a prerequisite for future nanomachines and nanodevices. In order to build a bistable molecular affinity switch, we have synthesized a supramolecular guest-host system whose binding affinity can externally be controlled and repetitively switched by UV light or heating. This photochemical macrocycle, which incorporates a supramolecular resorc[4] arene receptor cavity and two photodimerizable anthracene moieties, has been investigated by single-molecule force spectroscopy under external optical control which proved the repetitive and selective activation and deactivation at the level of individual molecular complexes. This synthetic photochemical single-molecule reaction acts as an intermolecular switch and can be affinity-tuned under external control, which allows new concepts for directed molecular assembly and motional functionalities at the nanoscale in the future.