Abstract: A polydiacetylene coating layer deposited upon an organic microcrystal. The coating has a large, uniform surface area which is monoriented and without cracks. The preferred embodiment utilizes for the monomer a layer of [1,6-di- n(carbazolyl)-2,4-hexadiyne] deposited by epitaxy onto an acid orthophthalate monocrystal of an alkali metal, ammonium or thallium. The process of the invention comprises cleaving the acid orthophthalate monocrystal along its (001) plane; depositing a diacetylenic monomer onto the cleaved face of the crystal by heat evaporation under vacuum conditions, and polymerizing the monomer upon the crystal face. The coated layer may thereafter be removed from the crystalline substrate by applying a composition such as, e.g., cabon or an acrylic polymer onto the coating to form a backing therefore and separating the resultant monoriented film from the crystal by at least partially immersing the coated crystal in water.

Abstract: At least one polydiacetylene compound is suitable for detecting whether an article has ever exceeded a selected temperature. The polydiacetylene compound is deposited on a substrate or mixed with a thermoplastic material. The polydiacetylene compound instantaneously and irreversibly changes from blue to red at the threshold temperature.