π-Conjugated oligothiophene-anthracene co-oligomers: Synthesis, physical properties, and self-assembly

A new class of oligothiophene-anthracene co-oligomers, 9,10-bis(2- dodecyloligothienylvinyl)anthracene T _n A (n = 1, 2 and 3), were synthesized and characterized. The photophysical and electrochemical properties of these oligomers demonstrated an increased conjugation length with increasing number of thiophene units. These oligomers also exhibited relatively larger ionization potential values compared with pentacene and sexithiophene and thus are expected to show improved stability. The strong aggregation tendency and excimer formation for T ₁ A and obvious aggregation effect for T ₂ A in solution were observed from the concentration and temperature-dependent fluorescence spectra. In contrast, no obvious aggregation behavior could be observed for T ₃ A in solution. Thermal behavior and self-assembly of these co-oligomers in solid state were studied by a combination of TGA, DSC, powder X-ray diffraction and polarizing optical microscope. Liquid crystalline phases were observed in T ₂ A and T ₃ A at elevated temperature while only a crystalline phase was found for T ₁ A. Single-crystal structures of T ₁ A and T ₂ A revealed a lamellar packing mode with ordered intermolecular anthracene-to-anthracene and oligothiophene-to-oligothiophene π-π stacking and these qualify them as potential semiconductors in electronic devices.