Azulene-based Semiconductor Materials

Azulene is a simple substance belonging to the class of compounds known as non-benzenoid aromatic hydrocarbons, and has attracted much attention because of its unusual properties, typified by large dipole moment and long-wavelength absorption properties. In this paper, we describe the synthesis, structures, properties, and organic field-effect transistor (OFET) characteristics of 2-azulenyl end-capped oligomers and 2,6-connected terazulene isomers. These compounds showed small transition energies due to their effective π-conjugation system, high-order orientations in the crystalline state, and typical OFET characteristics with high carrier mobilities. In particular, terazulene isomers reveal a unique π-conjugation system with an asymmetric distribution of molecular orbitals, which present an unconventional concept: polarity control of OFET achieved by molecular orbital distribution control. The molecular design, based on the 2,6-connected azulene-based π-conjugation, could be a key approach for constructing various semiconductor materials. Moreover, these findings provide a basis for accelerated development of the solid-state chemistry of azulene.