Isomer-Free Quinoidal Conjugated Polymers with Different Core Lengths for Organic Field-Effect Transistors

Abstract

Quinoid platforms have garnered considerable attention as promising candidates for conjugated building blocks because of their superior charge transport properties and high electrical conductivity. Because the quinoid structure can easily adjust the optoelectronic properties by controlling the length of the quinoid core, it has the advantage of choosing the desired purpose. However, double-bond linkages within the quinoid structure could generate geometric isomers, which hinder the purification process and understanding of a well-defined structure–property relationship. Herein, the conformational locking concept was exploited to fix the molecular configuration via intramolecular nonbonding S···O interactions using the 3,4-ethylene­dioxythiophene (EDOT) unit as a quinoid core. Two EDOT-based quinoidal building blocks with varying core lengths were simultaneously and easily obtained through the indophenine reaction and validated to have only one isomer-free configurational structure via nuclear magnetic resonance analysis. A vinylene unit was used as an aromatic counterpart to establish isomer-free quinoidal polymers with high coplanarity, leading to efficient charge transport. Two polymers are termed PQmEDOTV and PQbEDOTV. Both polymers exhibited changes in the optical and electrochemical properties in accordance with the core length of the quinoidal building blocks. Although the two polymers are composed of EDOT as the core, PQbEDOTV is significantly affected by the electron-donating nature of EDOT because it contains two EDOT units in the quinoidal backbone, resulting in more high-lying frontier molecular orbital levels compared to PQmEDOTV. Consequently, the PQmEDOTV- and PQbEDOTV-based organic field-effect transistors demonstrated ambipolar and unipolar p-channel operations with hole mobility up to 0.18 cm2 V–1 s–1, respectively.

Significant alternation of molecular structures and properties in quinoidal conjugated polymers by chalcogen atom substitution

“…6-Bromo-1-(2-decyltetradecyl)indoline-2,3-dione and mQEDOT-Br were synthesized using modified and previously reported procedures, respectively. 20,21,51 1 H NMR (400 MHz, CDCl 3 ) δ 7.84 (d, J = 8.4 Hz, 1H), 6.89 (d, J = 8.3 Hz, 1H), 4.63 (s, 2H), 3.44 (d, J = 7.1 Hz, 2H), 1.73 (s, 1H), 1.24 (s, 40H), 0.87 (t, J = 6.3 Hz, 6H).…”

Recent Research Progress in Indophenine-Based-Functional Materials: Design, Synthesis, and Optoelectronic Applications

“…Using a similar strategy, O⋯S non-covalent interactions and steric repulsion were employed towards the synthesis of bis-QEDOT, compound 17 [ 53 ]. Similarly, Kim et al found that compound 17 and 18 were synthesized simultaneously by the indophenine reaction under sulfuric acid catalytic conditions with yields of 40% and 12%, respectively [ 54 ]. Both quinoid monomers were confirmed to have a single geometric structure with NMR analysis, which also confirms the intramolecular nonbonding S···O interactions.…”

Isomer-Free Quinoidal Building Block Employing 3,4-Phenylenedioxythiophene Unit with Mesomeric Effect for Low-Bandgap Quinoidal Conjugated Polymers

“…In addition, several isatin-terminated quinoidal bithiophene (QuBT) derivatives have been developed by modifying thiophene moieties between isatin rings, such as fused thiophene rings, 3,4-dimethoxythiophene (DMOT), 3,4-ethylenedioxythiophene (EDOT), and 3,4-propylenedioxythiophene (ProDOT), entailing the suppression of geometrical isomers (Figure ). − Such synthetic versatility allows for the development of several QCPs as well as small molecules, which have been applied to unipolar or ambipolar organic field-effect transistors (OFETs) as active materials. − …”