High hole mobility of benzo-2,1,3-thiadiazole polycrystals formed by utilizing self-assembly property of liquid crystalline mesophase

4,7-Di(p-alkoxyphenyl)-2,1,3-benzothiadiazoles having linear alkyl chains were prepared by the Suzuki-Miyaura coupling reaction of 4,7-dibromo-2,1,3-benzothiadiazole with the corresponDing p-alkoxyphenylboronic acids. All compounds exhibited stable crystalline phase 1 (Cr1), quasi-stable polycrystalline phase 2 (Cr2), smectic liquid crystalline phase (A and C), and isotropic liquid. By conventional time-of-flight measurement using N2 laser, the hole mobility of benzothiadiazole derivatives was evaluated to be about 1×10%1cm2V%1 s%1 in the Cr1 phase, while the hole mobility of these in the smectic phases was on the order of 10%4-10%5cm2V%1 s%1. From a powder X-ray diffraction analysis, it was demonstrated that the interlayer spacing in the Cr1 phase was smaller than those in the smectic A and C phases. Microscopy observation of the polycrystalline films showed that the films in the Cr1 phase had less grain boundary structure. The high hole mobility of the benzothiadiazole derivatives in the Cr1 phase may be due to their small interlayer spacing and less grain boundary structure.