Photochromic dihetarylethenes 4. The molecular and crystal structures of 1,2-bis(2-ethyl-5-ethylsulfonylthien-3-yl)perfluorocyclopentene and 1,2-bis [5-(benzoxazol-2-yl)-2-methylthien-3-yl] perfluorocyclopentene

The structures of two hetarylethene photochromes, viz., 1,2-bis(2-ethyl-5-e thylsulfonylthien-3-yl)perfluorocyclopentene and 1,2-bis[5-(benzoxazol-2-yl )-2-methylthien -3-yl]perfluorocyclopentene, were established by X-ray diff raction 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 perfluorocyclopen tene fragments by similar to 55 degrees. The thiophene and benzoxazole ring s in 1,2-bis[5-(benzoxazol-2-yl)-2-methylthien-3- yl]perfluorocyclopentene are coplanar.