Novel Organosilicon Tetramers with Dialkyl-Substituted [1]Benzothieno[3,2-b]benzothiophene Moieties for Solution-Processible Organic Electronics

The synthesis, phase behavior and semiconductor properties of two novel organosilicon tetramers with dialkyl-substituted [1]benzothieno[3,2-b]benzothiophene (BTBT) moieties, <b>D4-Und-BTBT-Hex</b> and <b>D4-Hex-BTBT-Oct</b>, are described. The synthesis of these molecules was carried out by sequential modification of the BTBT core by carbonyl-containing functional alkyl substituents using the Friedel-Crafts reaction, followed by the reduction in the keto group. The target tetramers, <b>D4-Und-BTBT-Hex</b> and <b>D4-Hex-BTBT-Oct</b>, were obtained by the hydrosilylation reaction between tetraallylsilane and corresponding 1,1,3,3-tetramethyl-1-(ω-(7-alkyl[1]benzothieno[3,2-b]benzothiophen-2-yl)alkyl)disiloxanes. The chemical structure of the compounds obtained was confirmed by NMR ¹H-, ¹³C- and ²⁹Si-spectroscopy, gel permeation chromatography and elemental analysis. Their phase behavior was investigated by differential scanning calorimetry, polarization optical microscopy and X-ray diffraction analysis. It was found that <b>D4-Und-BTBT-Hex</b> shows higher crystallinity at room temperature as compared to <b>D4-Hex-BTBT-Oct</b>, while both molecules possess smectic ordering favorable for active layer formation in organic field-effect transistors (OFETs). The active layers were applied by spin-coating under conditions of a homogeneous thin layer formation with a low content of defects. The devices obtained from <b>D4-Und-BTBT-Hex</b> have demonstrated good semiconductor characteristics in OFETs with a hole mobility up to 3.5 × 10^-2 cm² V^-1 s^-1, a low threshold voltage and an on/off ratio up to 10⁷.