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

In the crystal structures of four thio­phene derivatives, (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. The crystal packing is determined by van der Waals inter­actions and some weak, relatively short, C—H...S and C—H...π directional contacts.