Synthesis of oligo(thienylfuran)s with thiophene rings at both ends and their structural, electronic, and field-effect properties

Oligo(thienylfuran)s with thiophene rings at both ends (SOSO-SOS, DE-SOSOS, DH-SOSOS, DE-SOSOSOS, and DH-SOSOSOS; S and 0 denote thiophene and furan rings, respectively, DE and DH denote diethyl- and dihexyl-substituted, respectively) were newly synthesized by repetitive Stille coupling reactions. The UV/ Vis maximum absorptions of the oligomers, SO, SOSO, SOSOS, SOSOSO, and SOSOSOS, exhibited a clear bath-ochromic shift with increasing number of heterocycles. The value of the oxidation peak potential (E-pa(1)) determined by cyclic voltammetry decreased with an increase in the number of heterocycles by 0.06-0.08 V per heterocycle. The crystal-packing structures of DE-SOSOS and DH-SOSOS determined by X-ray crystallography have a herringbone motif and are denser than the reported structures of pentacene and alpha-sexithiophene. The morphologies of thin films prepared by vacuum deposition and spin coating were investigated by atomic force microscopy and X-ray diffraction. Among these films, those of DE-SOSOS and DH-SOSOS exhibited highly ordered arrangements. The devices based on vacuum-deposited and spin-coated films of DE-SOSOS and DH-SOSOS displayed the highest FET mobilities of 10(-2)-10(-3) cm(2) V-1 s(-1) among the oligomers reported in this study.