Synthesis and Transistor Properties of Asymmetric Oligothiophenes: Relationship between Molecular Structure and Device Performance

A series of three thiophene-naphthalene-based asymmetric oligomers5-decyl-2,2:5,2:5,2-quaterthiophene (DtT), 5-decyl-5-(naphthalen-2-yl)-2,2:5,2-terthiophene (D3TN), and 5-(4-decylphenyl)-5-(naphthalen-2-yl)-2,2-bithiophene (DP2TN)was synthesized by Suzuki cross-coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self-assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H-type aggregates with a face-to-face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing-incidence wide-angle X-ray scattering. These oligomers were used as the active layers of p-type organic field-effect transistors, and the resulting devices showed field-effect mobilities of 3.3x10(-3)cm(2)V(-1)s(-1) for DtT, 1.6x10(-2)cm(2)V(-1)s(-1) for D3TN, and 3.7x10(-2)cm(2)V(-1)s(-1) for DP2TN. The differences in transistor performances were attributed to the degree of overlap and the morphological differences determined by the molecular structures.