Achieving perpendicular alignment of rigid polythiophene backbones to the substrate by using solvent-vapor treatment

The perpendicular orientation of rigid poly(3-butylthiophene) (P3BT) backbone to the substrate was achieved by using solvent-vapor treatment so that the thickness of the crystal could be substantially increased. The crystallographic transition of P3BT from Form I to Form II took place as the specimen was exposed to CS₂ vapor. The polymorphic behavior of polythiophene was found on regioregular P3AT with longer side chains, such as poly(3-octylthiophene) and poly(3-decylthiophene) because of the strong packing tendency of the long side-substituted alkyl segment. The short alkyl-substituted polythiophene P3BT could adopt the unusual Form II modification, which is a stable phase from athermodynamic point of view. Form II was more thermodynamically stable modificationas it was obtained by slow solvent evaporation, while Form I was kinetically determined phase.