Publisher Summary A considerable number of (2+2) photocycloadditions is known. Among them, some aromatic molecules, and cinnamic like compounds give photoreversible or thermally reversible cycloadducts. The spectral variation between the addends and the cyclobutane cycloadducts can be modulated according to the selected chromophores within a range of about 350 nm (250–600 nm). The reactions are studied in organic solvents, and in polymers and the crystalline state. A number of these reactions are found to be clean, giving rise to a single product, in an intramolecular process that is of advantage to perform cycles of cycloaddition and dissociation in a solid matrix. Like in many other organic molecules, oxidation can be a limitation for their application in devices but the photochromic properties of these systems have not yet been systematically investigated.