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 center dot center dot center dot 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.