An iodine effect in ambipolar organic field-effect transistors based on indigo derivatives

5,5'-Diiodoindigo (4) exhibits excellent ambipolar transistor properties with hole/electron mobilities of mu(h)/mu(e) = 0.42/0.85 cm(2) V-1 s(-1). The halogen substituted indigos show decreasing tilt angles from F to I in the crystals. In addition, the iodine-iodine interaction provides extraordinarily large interchain interaction. However, the X-ray diffraction suggests that the indigo molecules are arranged approximately perpendicular to the substrate in the thin films, probably due to the extra iodine-iodine interaction. The remarkable performance is ascribed to this characteristic supramolecular interaction.