2,2′′,3,3′′,4,4′′,5,5′′-Octaphenyl-1,1′:4′,1′′-terphenyl and 2′,3′,5′,6′-tetrafluoro-2,2′′,3,3′′,4,4′′,5,5′′-octaphenyl-1,1′:4′,1′′-terphenyl

The title compounds, C66H46, (I), and C66H42F4, (II), are polyphenylated arylenes synthesized by one‐step Diels–Alder cycloaddition reactions. In both structures, all molecules lie on crystallographic inversion centers. In the case of (I), there are two half‐molecules present in the asymmetric unit, (IA) and (IB); the geometry of each half‐molecule differs principally in the magnitudes of the dihedral angles between mean planes fitted through the central aryl ring and the pendant phenyl rings. The crystal used was a non‐merohedral twin, with a refined twin scale factor of 0.460 (8). The dihedral angle between the plane of the central tetrafluorinated ring and the adjacent tetraphenylated ring in (II) is 83.87 (4)°, significantly greater than the dihedral angles of 49.89 (12) and 54.38 (10)° found in the two half‐molecules in (IA) and (IB), respectively, and attributed to intermolecular C—H...F hydrogen bonding in (II). Intermolecular C—H...π bonding is found in (I). Two interactions have the C—H bond oriented towards the centroid (Cg) of a butadiene fragment of a phenyl ring; both H...Cg distances are approximately 2.68 Å and the interactions connect adjacent molecules into stacks in the c‐axis direction. The composition of the stacks alternates, i.e. (IA)–(IB)–(IA)–(IB) etc. A third, weaker, C—H...π interaction and a phenyl–phenyl close contact connect each end of the long molecular axes of (IB) with an adjacent molecule of (IA) into chains which run perpendicular to the (140) and (40) planes. C—H...F interactions in (II) have the most profound influence on the molecular and crystal structure, the main effect of which is the above‐mentioned increase in the dihedral angle between the plane of the central tetrafluorinated ring and the adjacent tetraphenylated ring. C—H...F interactions have refined H...F distances of 2.572 (15) and 2.642 (16) Å, with approximate C—H...F angles of 123 and 157°, respectively. These form a hydrogen‐bonded ribbon structure which propagates in the b‐axis direction.