3,4-Ethylenedioxythiophene-Based Isomer-Free Quinoidal Building Block and Conjugated Polymers for Organic Field-Effect Transistors

Since quinoidal molecules have double-bond linkages between aromatic rings, they have many advantages for efficient charge transport resulting from high planarity and extended p-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, H-1 NMR, and density functional theory calculation. Furthermore, thiophene (T), bithiophene (2T), and thienylene vinylene (TV) as pi-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 similar to 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 degrees 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 x 10(-2) (PQEDOT-T), 1.8 x 10(-2) (PQEDOT-2T), and 7.8 x 10(-3) cm(2) V-1 s(-1) (PQEDOT-TV).