Ferroelectric Organic Semiconductor: [1]Benzothieno[3,2- b ][1]benzothiophene-Bearing Hydrogen-Bonding -CONHC 14 H 29 Chain.

An alkylamide-substituted [1]benzothieno[3,2- b ][1]benzothiophene ( BTBT ) derivative of BTBT -CONHC 14 H 29 ( 1 ) and C 8 H 17 - BTBT -CONHC 14 H 29 ( 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 (-CONHC 3 H 7 ) derivatives revealed the coexistence of two-dimensional (2D) electronic band structures brought from a herringbone arrangement of the BTBT π core and the one-dimensional (1D) hydrogen-bonding chains of -CONHC 3 H 7 chains. The thin films of 1 and 2 fabricated on the Si/SiO 2 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 μ FET = 2.4 × 10 -5 cm 2 V -1 s -1 and threshold voltage V Th = - 29 V, whereas that of 2 showed a μ FET = 2.1 × 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 μC cm -2 and coercive electric field E c = 5.2 V μm -1 , whereas the P r and E c of 2 were 3.4 μC cm -2 and 7.0 V μm -1 at the conditions of 453 K and 1 Hz. Introduction of alkylamide units into the BTBT π core has the potential to develop the external stimulus-responsive organic semiconductors brought from both ferroelectricity and semiconducting properties.