Structure-Property Relationships in Quinoidal Conjugated Polymers Containing Different Length of Core

Abstract

Conjugated molecules containing quinoid structures have been extensively studied as organic electronics requiring efficient charge transport due to their high structural planarity arising from a double bond linkage between aromatic rings. Their planar structures induce a favorable π-electron delocalization over the whole backbone as well as an efficient intermolecular π-orbitals overlap; thereby, they manifested very promising charge transport properties. However, quinoid compounds have been rarely used as the building block for conjugated polymers. To achieve the incorporation of quinoidal platform into the polymer backbones, we have utilized an isatin unit which has bromine at 6-position possible to polymerization. Recently, we have reported quinoidal conjugated polymers incorporating an isatin-terminated quinoid units, quinoidal thiophene (QuT), with common aromatic rings. These polymers are applied to organic field-effect transistors as an active layer, and they showed high mobility over 2 cm2/Vs. In this research, we investigate the change of properties in accordance with the length the quinoid unit in the polymer backbone. Two quinoid monomers, QuT and quinoidal bithiophene (QuBT), were synthesized simultaneously via one-pot reaction. Then, two quinoid polymers based on these units, poly(quinoidal thiophene-thienylene vinylene) (PQuT-TV) and poly(quinoidal bithiophene-thienylene vinylene) (PQuBT-TV), were developed by copolymerization with a thienylene vinylene which has an extended conjugation. We discuss the correlation between the molecular structures and the various properties of these polymers.