Conjugated thiophene-containing oligoacenes through photocyclization: bent acenedithiophenes and a thiahelicene

The preparation of bent anthradithiophenes (BADTs) using an oxidative photocyclization-based synthetic strategy is reported. The optical properties of the new compounds were characterized by UV-vis and fluorescence spectroscopies, and the redox properties were probed by cyclic voltammetry. Structural studies using single crystal X-ray crystallography show that the unsubstituted BADT adopts a slipped cofacial stacking arrangement in the solid state with pi-pi interactions along the intermolecular stacking axis. The dialkylated derivatives adopt similar packing motifs with varying degrees of slipping along their long and short molecular axes while the diphenyl derivative packs into an edge-to-face herringbone arrangement. Powder diffraction data show that in thin films prepared by vacuum evaporation, molecules of the unsubstituted BADT are oriented nearly perpendicular to the substrate surface whereas the dialkylated derivatives adopt either multiple phases or new polymorphs. A thiahelicene prepared from the oxidative photocyclization of two isomers of 2,5-dithienyl-1,4-distyrylbenzene is described and the crystal structure reported.