Structural effects of dibromocarbazoles on direct arylation polycondensation with 3,4-ethylenedioxythiophene

Abstract

The direct arylation reaction of a C–H bond with aromatic halides has been employed as a novel environmentally-friendly polymerization method for producing conjugated polymers. In this article, 3,4-ethylenedioxythiophene (EDOT) was copolymerized with a series of dibromocarbazoles (Cbzs) by the phosphine-free and microwave-assisted direct arylation polycondensation. The microwave heating dramatically shortened the reaction time compared to conventional heating. Under optimal conditions, a solution processable linear polymer, 3,6-Cbz-EDOT, with the number-average molecular weight (M_n) of 5600 and polydispersity index (M_w/M_n) of 1.9 was successfully synthesized. In contrast, the other dibromocarbazole monomers with different substitution patterns, i.e., 2,7-Cbz and 1,8-Cbz, did not afford the corresponding soluble linear polymers due to the occurrence of undesired crosslinking and the poor reactivity caused by steric hindrance or unsuitable catalysts, respectively. The electrochromic properties of 3,6-Cbz-EDOT were investigated. The thin polymer film displayed two-step color changes with the increasing potentials. The first color change was highly reversible with the switching times of the coloring and bleaching processes being 3.2 and 2.0 s, respectively.