Versatile Protocol of C–H Direct Arylation Coupling Enables the Synthesis of Narrow-Band-Gap Polymers Containing Benzobisthiadiazole or Thiadiazoloquinoxaline Units
Feng Jiang, Xianjun Deng, Yuanhong Gao, Wenchang Wu, Yan Li, Xugang Guo, Hong Meng, Feng He, Mingfeng Wang
Abstract
π-Conjugated narrow-band-gap polymers (NBPs), characterized by their intrinsically electrical, optical, spintronic, and mechanical properties, have attracted broad interest since the development of the first generation of conducting polymers. The current synthesis of NBPs, nevertheless, largely relies on traditional Suzuki or Stille coupling, which often requires preactivation of aryl C–H bonds involving highly flammable organometallic reagents, such as butyl lithium and highly toxic stannyl agents, which are often involved in Stille coupling. Here, we report the synthesis of a series of NBPs consisting of benzobisthiadiazole (BBT) or thiadiazoloquinoxaline (BBQ) units via a “greener chemistry” of direct arylation polymerization (DArP). Free of toxic organotin compounds or extra borylation, our DArP protocol, in the presence of a Pd 2 (dba) 3 catalyst, phosphine ligands, and carboxylic acid additives enables efficient polymerization with monomers of BBT or BBQ with comonomers containing opposite reactive sites. Consequently, a series of donor–acceptor (D–A) or acceptor–acceptor (A–A) alternating copolymers have been synthesized in decent yields and with minimal defects. These polymers with narrow optical band gaps below 1.3 eV can achieve near-infrared (NIR) absorption and fluorescence emission, as well as stable electrochemical performance. Moreover, the scope of open-shell BBT- and BBQ-based polymers has been broadened, including a series of spin density and spin–orbit coupling, as well as tunable electron, hole, or ambipolar charge transport behavior.