Flip-type disorder in 3-substituted 2,2':5',2''-terthiophenes

In the crystal structures of four thiophene derivs., (E)-3'-[2-(anthracen-9-yl)ethenyl]-2,2':5',2''-terthiophene, C28H18S3, (E)-3'-[2-(1-pyrenyl)ethenyl]-2,2':5',2''-terthiophene, C30H18S3, (E)-3'-[2-(3,4-dimethoxyphenyl)ethenyl]-2,2':5',2''-terthiophene, C22H18O2S3, and (E,E)-1,4-bis[2-(2,2':5',2''-terthiophen-3'-yl)ethenyl]-2,5-dimethoxybenzene, C36H26O2S6, at least one of the terminal thiophene rings is disordered and the disorder is of the flip type. The terthiophene fragments are far from being coplanar, contrary to terthiophene itself. The central C-C=C-C fragments are almost planar but the bond lengths suggest slight delocalization within this fragment.