Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene
(BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N–H···O=
hydrogen-bonding network of alkylamide group and two-dimensional (2D)
electric structure of BTBT π-cores, was prepared
to design the external electric field-responsive organic semiconductors.
The short-chain derivative of BTBT-NHCOC3H7 (1’) revealed the coexistence of a 2D
electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412
K and showed ferroelectric hysteresis in the electric field–polarization
(P–E) curves at 403–433
K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 μC
cm–2 and 5.54 V μm–1, respectively.
By thermal annealing of thin-film 1 at 443 K, the molecular
assembly structure of 1 changed from a monolayer to a
bilayer structure with high crystallinity, resulting in conducting
layers of BTBT parallel to the substrate surface. The
organic field-effect transistor (OFET) device with thermally annealed
thin-film 1 showed p-type semiconducting behavior with
the hole mobility of 1.0 × 10–3 cm2 V–1 s–1. Furthermore, device 1 showed switching behavior of semiconducting properties by
electric field poling and thermal annealing cycle. The electric field
response of ferroelectrics modulated the molecular orientation and
conduction properties of organic semiconductors, resulting in external
electric field control of carrier transport properties.