The influence of terminal alkyl groups on the structure, and electrical and sensing properties of thin films of self-assembling organosilicon derivatives of benzothieno[3,2-b][1]benzothiophene

The synthesis and systematic investigation of organosilicon derivatives of benzothieno[3,2-b][1]benzothiophene (BTBT) with different lengths of terminal alkyl groups (from C2 to C13), or without them, capable of self-assembly at the water-air interface are described. All novel compounds were obtained with high yields and purity, which was proved by H-1, C-13 and Si-29-NMR spectroscopy, gel permeation chromatography and elemental analysis. The study of their phase behavior by differential scanning calorimetry and polarizing optical microscopy showed that all the compounds are crystalline at room temperature. However, at elevated temperatures those with terminal alkyl substituents form enantiotropic smectic A or C mesophases, while the compound without terminal alkyl groups forms a monotropic nematic mesophase. The increase of the alkyl chain length from C2 to C8 leads to higher temperatures of both phase transitions: from the crystal to the disordered smectic mesophase and to the isotropic melt. X-ray diffraction measurements confirm the presence of disordered SmA and SmC phases and the ordered SmE or SmK phase, and suggest models of their packing depending on the terminal alkyl chain length. The investigation of the electrical properties of monolayer OFETs based on these compounds and their sensing responses to NO2 revealed the dependence of charge carrier mobility values and sensitivity parameters mainly on the surface morphology of organic semiconductors. A comparison of the semiconducting and sensing properties of different compounds investigated revealed a weak correlation between these parameters, while the best characteristics were observed for the OFETs based on the siloxane dimer of BTBT with C8 terminal groups.

Automated summary

This study investigates the synthesis and behavior of organosilicon derivatives of benzothieno[3,2-b][1]benzothiophene (BTBT) at the water-air interface. The compounds with different lengths of terminal alkyl groups or without them were obtained with high yields and purity. The investigation showed that the compounds form crystalline phases at room temperature, but exhibit different mesophases at elevated temperatures depending on the presence and length of the terminal alkyl groups. The electrical properties of monolayer OFETs based on these compounds and their sensing responses to NO2 were also studied, revealing the dependence of charge carrier mobility and sensitivity parameters on the surface morphology of organic semiconductors.