C_3v-Symmetrical Tribenzotriquinacenes as Hosts for C₆₀ and C₇₀ in Solution and in the Solid State

Various tribenzotriquinacenes (TBTQs), most of which incorporate six functional groups at the periphery of their C_3v-symmetrical, rigid and convex−concave molecular framework, have been studied with respect to their ability to form supramolecular complexes with the C₆₀ and C₇₀ fullerenes, either in the solid state or in solution. The hexabromo derivative Br₆-TBTQ was cocrystallized with C₆₀ as [Br₆-TBTQ⊂C₆₀·toluene] but, as studied by UV/vis and ¹H NMR spectroscopy, aggregation in benzene, toluene, or carbon disulfide solutions was not observed. Likewise, in contrast to the related C_5v-symmetrical decakis(alkylthio)corannulenes, neither the parent hydrocarbon, nor a related hexamethoxy, or two hexakis(alkylthio) derivatives exhibited color, or complexation-induced chemical shift (CIS) changes with C₆₀ or C₇₀. The novel tris(2,3-thianthreno)triquinacene (o-S₂C₆H₄)₃-TBTQ, a TBTQ derivative extended by three 1,2-benzodithiino wings, and synthesized from Br₆-TBTQ, was found to form 1:1 complexes with C₆₀ and C₇₀ in both benzene and toluene solutions. Association constants were determined for the respective complexes, viz. (o-S₂C₆H₄)₃-TBTQ⊂C₆₀ (K_assoc = 977 ± 56) and (o-S₂C₆H₄)₃-TBTQ⊂C₇₀ (463 ± 49, both in benzene). The X-ray single crystal and molecular structures of the pure host and of the aggregates [(o-S₂C₆H₄)₃-TBTQ⊂2 C₆₀·2.5 chlorobenzene] were also determined.