Isomerically pure syn-/anti-anthradithiophene derivatives have been developed in the past few years. Although anti-isomers showed higher field-effect mobilities than mixture of isomers have been reported, a detailed comparison of syn-isomer and anti-isomer molecules has not been carried out. In this study, we took newly synthesized pure unsubstituted syn-/anti-anthradithiophenes (ADTs) and compared their single crystal structures, physical properties and semiconducting behavior with a previously studied syn-/anti-dimethylanthradithiophenes (DMADTs). Although the both isomers were typical herringbone packing structures with similar parameters, anti-isomers involved less disordered atoms in the crystal packing. The results from thermal analysis, UV-vis spectra, photo luminescence spectra and cyclic voltammograms of syn-/anti-anthradithiophenes were nearly the in the solid state as well as in solution. However, field-effect transistors showed obvious differences with mobilities of 0.12 cm(2) V(-1) s(-1) for anti-anthradithiophene and 0.02 cm(2) V(-1) s(-1) for syn-anthradithiophene. Because the crystallinity of thin-films measured by X-ray diffraction (XRD) and atomic force microscopy (AFM) seems to be better in syn-isomers, the differences in transistor performance are likely attributed to local defects affecting intermolecular interactions, such as disorder in the crystal packing and charge-dipole interactions.

Solution-processable polymers based on strong acceptor benzobis(thiadiazole) (BBT) units were synthesized to form unipolar n-type organic thin-film transistors (OTFTs) that were electronically characterized. These polymers exhibited a narrow band-gap and low LUMO level, resulting in distinct n-type semiconducting properties within the OTFT devices. The BBT–thiazole polymer material showed better electron transport than BBT–thiophene polymers. The use of electron-deficient units was found to be suitable for the realization of the unipolar n-type semiconducting polymers.

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Two newly developed narrow bandgap polymers containing benzobis(thiadiazole) (BBT) have been synthesized using the Stille coupling reaction. The polymers showed absorption in the near infrared region due to strong charge-transfer interactions in the donor-acceptor (D-A) units, suggesting a rigid planarized structure. Although both the HOMO-LUMO levels of the polymers lie close to the work function of gold electrodes, a BBT-quaterthiophene polymer showed only p-type semiconducting behavior. In addition, the dominant charge-carrier type is holes even in BBT-thiazole-thiophene polymers, which consists mainly of acceptor units, and indicates that the thiophene ring in these polymers has a strong influence on the charge transport properties.