Synthesis, characterization, and transistor response of tetrathia-[7]-helicene precursors and derivatives

In this paper we report polycyclic, fully-conjugated, heteroaromatic compounds 1-5, two of them having a helical shape (tetrathia-[7]-helicenes 1 and 2), and explore their potential use as p-type semiconductors for organic thin-film transistors (OTFTs). Furthermore, we describe their optical absorption, emission, and electrochemical properties. In addition, the single crystal X-ray diffraction structure for compound 3 is reported. Thin films of all compounds were fabricated on several substrates at different temperatures by physical vapor deposition, and were characterized by optical spectroscopy, wide-angle X-ray diffraction, atomic force microscopy, and TFT measurements. The AFM images of compound 1 exhibit an interesting tubular morphology for films deposited at room temperature. This is the first observation of a compound with a helical shape leading to a nanowire-like morphology. In agreement with the molecular structure/morphology, only compound 4 is a p-type semiconductor with good carrier mobility.