Racemic charge-transfer complexes of a helical polycyclic aromatic hydrocarbon molecule†
Single crystals of racemic charge-transfer complexes comprising a helical polycyclic aromatic hydrocarbon molecule, helicene, as the electron donor (D) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) analogs as the electron acceptor (A) were obtained via either co-sublimation or solvent evaporation. All complexes consist of heterochiral DA-type alternating π-columns with a [⋯(P)-helicene⋯TCNQ⋯(M)-helicene⋯TCNQ⋯] repeating unit, which show a peculiar wavy feature primarily related to the nonplanar geometry of the helicene molecules. Helicene molecules form a two-dimensional sheet intersecting the columns, and the molecular arrangement (namely, either homochiral or heterochiral arrangement) in the sheets depends on the TCNQ analog. Theoretical calculations were carried out to discuss the origin of the molecular deformation of helicene molecules in the CT solids in terms of intermolecular interactions.