A Defect-Free Naphthalene Diimide Bithiazole Copolymer via Regioselective Direct Arylation Polycondensation

TL;DR

This paper reports a regioselective direct arylation polycondensation method to synthesize a defect-free naphthalene diimide-bithiazole copolymer with high molecular weight, thermal stability, and promising electronic properties for organic devices.

Contribution

The study introduces a novel regioselective C-H activation approach for efficient, high-yield synthesis of a fully regioregular NDI-bithiazole copolymer without defects.

Findings

High molecular weight copolymer achieved in less than 1 hour

Copolymer exhibits high thermal stability and favorable electronic properties

Regioselective activation at 5-position is key to synthesis success

Abstract

An optimized direct arylation polycondensation (DAP) protocol for the synthesis of a novel naphthalene diimide (NDI) 2,2'-bithiazole (2-BTz) copolymer (PNDI-2-BTz) is presented. The regioselective C-H activation of 2-BTz at the 5-positions allows for the synthesis of fully regioregular and homocoupling-free PNDI-2-BTz of high molecular weight in less than 1 h in quantitative yield. Complete end group assignment shows functionalities according to monomer structures or to nucleophilic substitution, and allows for the reliable determination of absolute molecular weight. Compared to the well-known bithiophene analog PNDIT2, an exceptionally high thermal stability, a hypsochromically shifted charge transfer absorption band and a lower-lying LUMO energy level is found, making PNDI-2-BTz an interesting candidate for applications in organic electronic devices. In contrast to the selective and high yielding C-H activation of 2-BTz at the 5-position, the regioisomer 5,5'-bithiazole is inactive under a variety of conditions.