Photochromic dihetarylethenes

Abstract

The structures of two hetarytethene photochromes, viz., 1.2-bis(2-ethyl-5ethylsulfonylthien-3-yl)perfluorocyclopentene and 1.2-bis[5-(benzoxazol-2-yl)-2-methylthien-3-yllperfluorocyclopentene, were established by X-ray diffraction analysis. The conformational parameters of the title compounds are considered. The cyclopentene ring in the former compound is planar and this ring in the latter compound adopts an envelope conformation. There are no overall conjugated systems in the molecules under study. In both structures, the dihetaryl fragments are rotated with respect to the perfluorocyclopentene fragments by -55 ~ The thiophene and benzoxazole rings in 1.2-bisl5-(benzoxazol-2-yl)-2-methylthien-3yljperfluorocyclopentene are coplanar.

The structure and characteristics of photochromic dithienylethenes

“…The full photoreversibility of isomers at the irradiation of ethanolic solution of form 3A by the light λ = 313 nm and form 3B-by the light λ = 578 nm is common for 1,2-bis[5-(benzoxazol-2-yl)-2-methylthien-3-yl]perfluorocyclopentene (3) [22] (Scheme 4). The structure of 3A [20] made up of two crystallographically independent molecules slightly differing only by deflection angles of benzoxazole fragments (B) relative to thiophene cycles and by torsion angles in cycle F. Contrary to structures of 1A and 2A cycle F in this compound has a form of envelope with a vertex, lying opposite to double bond. Other peculiarity of compound 3 is the formation of plane spatially elongated conjugated system thiopene-benzoxazole.…”

“…The molecule of 1,2-bis(2-ethyl-5-ethylsulfonylthien-3-yl)perfluorocyclopentene (2) which is isomer of 2A (Scheme 3), has C 2 symmetry in crystal and is similar to 1A molecule [20]: cycle F is flat, dihedral angles T/F are equal to 56, 4 0 ; dihedral angle between symmetric thienyl cycles is equal to 51, 4 0 . Ethyl groups in thienyl cycles are at different sides of ring plane of F.…”