π‐Conjugated Polymers Incorporating a Novel Planar Quinoid Building Block with Extended Delocalization and High Charge Carrier Mobility

Abstract

Conjugated polymers have been extensively studied as organic semiconductors and investigated for various applications such as flexible displays and printed electronics due to their mechanical flexibility and solution processability. In particular, molecular design, synthesis, and structure-property relationship of ?- conjugated polymers have been intensively researched. A quinoid structure is a molecular conformation in which aromatic rings are connected by double bonds. Their high molecular planarity arisen from double bond linkage induces a favorable intramolecular ?-electron delocalization and an efficient intermolecular overlap of ?-orbitals, leading to improving charge transport. Moreover, they have unique features such as low electronic band-gap and amphoteric redox properties. Here, we present two conjugated polymers, PQuT-T and PQuT-BT, incorporating quinoidal thiophene by substituting isatin termini. By combining 1D-, 2D-COSY, and NOESY NMR analyses, the isomeric form of the major quinoidal moiety is clearly identified as the asymmetric Z, E-configuration. These quinoidal moiety contributed greatly not only to narrow band-gap but also to achieve high mobility in organic field-effect transistors. Charge transport properties of quinoidal polymers are enhanced by chain alignment via simple solution processing technique using centrifugal force, with PQuT-BT exhibiting a high hole mobility of 8.09 cm2 /Vs.