Photoresponsive functional systems have been studied across a broad range of research disciplines, including nanomachinery, optical data storage, photopharmacology, smart materials and solar energy storage. Such molecules can switch between thermally stable and metastable isomers, typically accompanied with changes in colour and/or structure. Transformations from a thermally stable isomer to a metastable structure is typically driven by light, while the reverse process can be driven either photochemically or thermally. A large collection of photoswitchable skeletons have been developed, with their transformations roughly separable into two modes of photoisomerization process: (1) photochemical double-bond E/Z-isomerization reactions (i.e., stilbenes, azobenzenes, indigos and iminothioindoxyls ), and (2) photochemical cyclization reactions (i.e., spiropyrans, diarylethenes and norbornadienes ). While photoswitching based on double-bond isomerization is frequently employed, lighttriggered cycloisomerization reactions that prompt the formation/cleavage of chemical bonds are less frequently encountered as molecular-switching modes-of-action. For the latter systems, switching via cycloisomerization typically relies on a 6π-cyclization (Figure ) or an intramolecular [2+2] cyclization of an unconjugated alkene (Figure ). Efforts has been made to design and synthesize photoresponsive molecules with improved switching properties for specific purposes toward energy storage or switchable material modification. These applications demand features including the complete conversion between isomers, high thermal stability of the metastable state, large geometrical changes upon isomerization and visible-light sensitivity. Some of these properties are easier to achieve through photoinduced pericyclic reactions than double-bond isomerisation, yet there are only a few reports featuring photoswitches based on the former principle. Most photoswitchable systems feature switching isomers that are similar in size and volume, making the observation of conformational flexibility not obvious and therefore hard to characterize. This lowers the efficiency of isomerization-mediated power transmission in specific applications, such as molecular machines. Switching systems that employ photocyclization possess favourable properties upon comparison to switches based on double-bond isomerisation-especially higher thermal stabilities and larger enthalpy differences between isomers -making them excellent candidates for emerging applications such as solar energy storage, molecular logic gates and smart materials. Therefore, there is a clear impetus to design novel photoresponsive systems that photocyclize with larger geometrical changes, experience less fatigue and are easily functionalized, all while maintaining a good switching efficiency alongside thermal stability.