We have determined crystallographic structures of four thiophene/phenylene co-oligomers with different molecular shapes. The compounds consist of the molecules straight, bent, or zigzag. All the crystals are monoclinic with space group either P21/c or P21/n, Z = 4, and the unique axis of b. The crystals are characterized by the presence of the molecular layered structure in which the molecules form the well-known herringbone structure laterally spreading along the ab-plane. We investigate the molecular disposition in the crystals and present its peculiarity in relation to those comprising nonstraight molecules (e.g., bent or zigzag). The specific effects upon optical characteristics produced by this peculiarity are mentioned.