Several natural products contain 8-membered ring structures, with many of those being active pharmaceuticals. Other related medium-sized ring structures also find applications including fragrances or as ligands in catalysts. However, the search for alternate applications of 8-membered ring structures (especially photoswitches) has been hindered by synthetic challenges. Based on new insights in metalloradical catalysis, we recently developed a facile method to prepare different kinds of 8-membered rings in high yields. Herein, we explore the photochemical and thermal reactivity of 1H-2benzo [c]oxocins (8-membered O-heterocycles), which lead to the development of a novel photothermallyswitchable system based on reversible chemical conversion between 1H-2-benzo [c]oxocins and dihydro-4Hcyclobuta [c]isochromenes (Figure 1C, top). These reactions are based on reversible cyclizations, proceed with excellent efficiency and are accompanied by large geometrical changes. The photoisomerization process exhibits excellent unidirectionality, can be performed in air using non-damaging visible light, and the process is independent on the solvent used. Furthermore, the metastable state demonstrates excellent thermal stability and the molecular skeleton is easy to functionalize. The combination of these properties are ideal to develop a new smart-material platform in follow-up studies.