The structure and characteristics of photochromic dithienylethenes

Abstract. The data on X-ray diffraction analysis for dihetarylethenes with perfluorocyclopentene (F), maleic anhydride (M) and cyclobutenedione (S) bridges between thienyl fragments were summarized and their photochromic properties were discussed. It was established that benzoxazole and benzothiazole substituents in position 5 of thienyl rings are coplanar to the plane of thiophene cycles. Thienyl fragments in A form of all dithienylethenes are considerably turned relative to the plane of bridging cycle. It means that there is no conjugation between π -electrons of aromatic heterocycles and double bond of the bridge. Flattening of molecule framework and the envelope conformation of thienyl cycles because of aromaticity loss are characteristic features of the form B structure with F-bridge. In all cases (excluding the compounds with alkylthio substituents in position 2 of thiophene cycle) the photochromic transition A −→ B is observed independently of different nature and structure of functional groups

Thermally irreversible photochromic dithienylethenes

Abstract. A lot of previously unknown derivatives of dithienylperfluorocyclopentene (DTPFCP) were synthesized. It was shown that 2, 2 -dialkylsubstituted DTPFCP'S are phtochromes. The quantum yields of forward and backward photochemical reactions and spectral parameters of open and cyclic forms of the photochromes synthesized were measured. An attempt to obtain fluorescing phtochromes by means of introduction of benzoxazolyl, benzthiazolyl and 1,2,4-oxadiazolyl moieties in 5 and 5 positions of DTPFCP failed; these compounds were synthesized but they do not fluoresce