A Novel Isomer-Free and Low-Lying Energy Level Quinoidal Conjugated Polymer Employing Planar Thiophene Derivative Core

Recently, the quinoid-type molecules and polymers have been considered as attracting semiconducting materials for organic electronics due to their interesting properties such as superior electrical properties, very low band gap and spin characteristics. For the development of quinoidal building blocks, the rational design of isomer-controllable core containing quinoid materials has been considered as an important issue since the presence of geometrical isomers limits the systematic investigation of their chemicophysical properties based on structure-property relationship.<br/>In this work, a novel isomer-free and low-lying energy level isatin-terminated quinoid molecule incorporating extended aromatic rings in quinoid core was designed and synthesized by simple indophenine reaction, then a novel conjugated polymer using the prepared quinoidal monomer was synthesized. It was found that the developed quinoidal building block exhibited the single isomer configuration, accomplished by steric hindrance between aryl rings and electrostatic intramolecular interaction. In addition, the employment of aromatic rings in quinoid core had effects on the decrease of the electron-releasing mesomeric effect into conjugated backbone, resulting in significant red-shift (~ 200 nm) absorption and dramatic downshifting both HOMO (~ 0.3 eV) and LUMO (~ 0.6 eV) energy levels. The charge transport capability of the prepared quinoidal conjugated polymer was evaluated by fabricating the organic field-effect transistors (OFET), exhibiting the balanced ambipolar charge transport mobilites in both p- and n-channels.