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 A 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 (\overline{1}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) A, 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.