Synthesis and Properties of Dicyanomethylene-Endcapped Thienopyrrole-Based Quinoidal S,N-Heteroacenes

Abstract

Abstract A new series of highly π-extended dicyanomethylene-endcapped quinoidal S,N-heteroacenes (JH-quinoids) fused with thiophene and pyrrole rings have been designed and synthesized. The π-extension of the central S,N-heteroacene cores gives rise to significant red-shifted absorption maxima in solution without being affected by the long alkyl groups. The absorption maximum of JH10 with the longest quinoidal backbone in the thin film significantly red-shifted to the near-infrared region of 1260 nm as compared to that in solution (880 nm), indicating the formation of strong intermolecular interaction in the solid state. JH-quinoids maintain sufficiently low LUMO energy levels in the range of −4.09∼−4.22 eV regardless of the fused ring systems and substituents, while the HOMO energy levels increase with extending the length of S,N-heteroacenes; the highest HOMO energy level of JH10 is as high as −5.18 eV owing to the contributions from the nitrogen atoms and chalcogen. The molecular geometries of JH-quinoids optimized from the DFT calculations indicate their complete planar backbones and the trend of HOMO and LUMO energy levels variation is in good agreement with the cyclic voltammetry results. Consequently, the present JH-quinoids should be promising candidates for ambipolar organic semiconductors.