Naphthyl and Thionaphthyl End-Capped Oligothiophenes as Organic Semiconductors: Effect of Chain Length and End-Capping Groups

• Published in: Advanced functional materials 2007-08, Vol.17 (12), p.1940-1951
• Main Authors: Tian, H. K., Shi, J. W., He, B., Hu, N. H., Dong, S. Q., Yan, D. H., Zhang, J. P., Geng, Y. H., Wang, F. S.
• Format: Article
• Language: English
• Subjects: Field-effect transistors; Field‐effect transistors, organic; organic; Organic semiconductors; Structure-property relationships; Thiophenes
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200706198

Two series of oligothiophenes (OThs), NaTn and TNTn (n = 2–6 represents the number of thiophene rings), end‐capped with naphthyl and thionaphthyl units have been synthesized by means of Stille coupling. Their thermal properties, optical properties, single crystal structures, and organic field‐effect transistor performance have been characterized. All oligomers display great thermal stability and crystallinity. The crystallographic structures of NaT2, NaT3, TNT2, and TNT3 have been determined. The crystals of NaT2 and NaT3 are monoclinic with space group P21/C, while those of TNT2 and TNT3 are triclinic and orthorhombic with space groups P$_{\bar 1}$ and P212121, respectively. All oligomers adopt the well‐known herringbone packing‐mode in crystals with packing parameters dependent on the structure of the end‐capping units and the number of thiophene rings. The shorter intermolecular distance in NaT3 compared to NaT2 indicates that the intermolecular interaction principally increases with increasing molecular length. X‐ray diffraction and atomic force microscopy (AFM) characterization indicate that the NaTn oligomers can form films with better morphology and high molecular order than TNTn oligomers with the same number of thiophene rings. The NaTn oligomers exhibit mobilities that are much higher than those for TNTn oligomers (0.028–0.39 cm2 V–1 s–1 versus 0.010–0.055 cm2 V–1 s–1, respectively). In particular, the NaTn oligomers with n = 4–6 all show a mobility higher than 0.1 cm2 V–1 s–1. This device performance is among the best in aryl end‐capped OThs, and indicates that naphthyl is an effectual building block for designing high‐performance organic semiconducting materials. High‐performance organic semiconductors have been prepared y end‐capping oligothiophenes with naphthyl (NaTn) and thionaphthyl (TNTn) groups (see figure). Organic field‐effect transistors fabricated from the NaTn compounds show a much superior performance than those fabricated from the TNTn compounds. Mobilities that are above 0.1 cm2 V–1 s–1 with high Ion/Ioff and low VT are achieved.