Classification of crystal structures of thiophene-containing organic semiconductors

Abstract

Oligothiophenes and thienoacenes are essential components of organic semiconductors and usually form herringbone structures with dihedral angles of θ = 50–60°. However, when more than three thiophene rings are fused, a stacking structure with θ = 125–130° appears. Since the molecules are located on a lattice point, the lattice constants as well as the intermolecular geometry are obtained by a simple relation of θ and the molecular size. Stacking structures are preferred when the peripheral hydrogen atoms are lost or when polar oxygen atoms are included. Coronene and ovalene with more than a three-ring width form a stacking structure called the γ-structure with θ = 90°, and some molecules form pitched π-stacking with a nonparallel terminal contact, where the intermolecular geometry is obtained by the same relation as the herringbone structures. For the molecular rotation of the γ-structure within the molecular plane, the nonparallel contact is usually formed using the molecular zigzag edge.