Photochromism (from Greek φωζ photo “light” and χρωμα chroma “colour”) is determined as reversible transformation between two chemical species, induced by action of light . Herewith, initial form and photoinduced isomer have different physical and chemical properties. The phenomenon is attractive for the design of hi-tech materials, including optical memory elements and molecular switches.
Diarylethenes is the most promising class of organic photochromic compounds due to outstanding thermal stability of both isomers and high photostability . The size of so-called ethene bridge significantly affects the photochromic reaction. The photochromic diarylethenes with 4-, 5-, and 6-membered cyclic ethene bridge are known, but there is no example with 3-membered bridge.
In this study we report a new approach towards dithienylacetylenes 3 that include the synthesis of diarylcyclopropenones 2 via Friedel-Crafts alkylation of heterocyclic compounds 1 with tetrachlorocyclopropene and following UV-irradiation. It was found that the diarylethenes 2 do not display photochromic properties, but they undergo quantitative photoelimination of carbon monoxide upon UV-irradiation resulting in dithienylacetylene 3. Thus, we have proposed a new synthetic two-step approach to dithienylacetylenes 3 , which could be useful synthons in synthesis of photochromic diarylethenes with various ethene bridges.