3,4-Ethylenedioxythiophene-Based Isomer-Free Quinoidal Building Block and Conjugated Polymers for Organic Field-Effect Transistors
2020
Since
quinoidal molecules have double-bond linkages between aromatic
rings, they have many advantages for efficient charge transport resulting
from high planarity and extended π-conjugation length. However,
they unavoidably generate some isomers, which cause difficulty in
purification and characterization. In this study, sulfur–oxygen
conformation locking and steric repulsion approach is introduced to
manipulate syn- and anti-isomerization of a quinoidal building block
(bis-QEDOT). As a result, isomer-free bis-QEDOT is synthesized by
introducing the 3,4-ethylenedioxy group, and the geometrical structure
of bis-QEDOT is identified by thin-layer chromatography, 1H NMR, and density functional theory calculation. Furthermore, thiophene
(T), bithiophene (2T), and thienylene vinylene (TV) as π-conjugated
building blocks are polymerized with bis-QEDOT. Due to the quinoid
structure, PQEDOT-T, PQEDOT-2T, and PQEDOT-TV show an intensified
near-IR absorption and a low band gap around ∼1.16 eV. Grazing
incidence wide-angle X-ray diffraction reveals that three quinoidal
polymers show in the (h00) diffraction peaks up to
third order after thermal annealing at 250 °C, demonstrating
high crystallinity of the films. Finally, the electrical properties
of the three polymers are investigated as an active layer in organic
field-effect transistors showing hole mobilities of 4.3 × 10–2 (PQEDOT-T), 1.8 × 10–2 (PQEDOT-2T),
and 7.8 × 10–3 cm2 V–1 s–1 (PQEDOT-TV).
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