Ferroelectric Organic Semiconductor: [1]Benzothieno[3,2-b][1]benzothiophene-Bearing Hydrogen-Bonding-CONHC14H29 Chain

An alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-CONHC14H29 (1) and C8H17-BTBT-CONHC14H29 (2) were prepared to design the multifunctional organic materials, which can show both ferroelectric and semiconducting properties. Single-crystal X-ray structural analyses of short-chain (-CONHC3H7) derivatives revealed the coexistence of two-dimensional (2D) electronic band structures brought from a herringbone arrangement of the BTBT pi core and the one-dimensional (1D) hydrogen-bonding chains of -CONHC3H7 chains. The thin films of 1 and 2 fabricated on the Si/SiO2 substrate surface have monolayer and bilayer structures, respectively, resulting in conducting layers parallel to the substrate surface, which is suitable for a channel layer of organic field-effect transistors (OFETs). The thin film of 1 indicated a hole mobility mu(FET) = 2.4 x 10(-5) cm(2) V-1 s(-1) and threshold voltage V-Th = - 29 V, whereas that of 2 showed a mu(FET) = 2.1 x 10(-2) cm(2) V-1 s(-1) and threshold voltage V-Th = -9.7 V. Both 1 and 2 formed the smectic E (SmE) phase above 410 and 369 K, respectively, where the existence of a hole transport pathway was confirmed in the SmE phase. The ferroelectric hysteresis behavior was observed in bulk 1 and 2 in the polarization-electric field (P-E) curves at the SmE phase. 1 showed the remanent polarization P-r = 2.3 mu C cm(-2) and coercive electric field E-c = 5.2 V mu m(-1), whereas the P-r and E-c of 2 were 3.4 mu C cm(-2) and 7.0 V mu m(-1) at the conditions of 453 K and 1 Hz. Introduction of alkylamide units into the BTBT pi core has the potential to develop the external stimulus-responsive organic semiconductors brought from both ferroelectricity and semiconducting properties.

Automated summary

In this study, alkylamide-substituted BTBT derivatives were prepared, which exhibited ferroelectric and semiconducting properties. The coexistence of two-dimensional electronic band structures was observed due to the herringbone arrangement of the BTBT pi core and the hydrogen-bonding chains of alkylamide units. The thin films of the derivatives showed suitable structures for organic field-effect transistors, with conducting layers parallel to the substrate surface. The introduction of alkylamide units also provided the potential for external stimulus-responsive organic semiconductors.