Synthesis of Conjugated Polymers via Transition Metal Catalysed C−H Bond Activation

Abstract

Transition metal catalysed CÀ H bond activation chemistry has emerged as an exciting and promising approach in organic synthesis. This allows us to synthesize a wider range of functional molecules and conjugated polymers in a more convenient and more atom economical way. The formation of CÀ C bonds in the construction of piconjugated systems, particularly for conjugated polymers, has benefited much from the advances in CÀ H bond activation chemistry. Compared to conventional transitionmetal catalysed cross-coupling polymerization such as Suzuki and Stille cross-coupling, pre-functionalization of aromatic monomers, such as halogenation, borylation and stannylation, is no longer required for direct arylation polymerization (DArP), which involve CÀ H/CÀ X cross-coupling, and oxidative direct arylation polymerization (Ox-DArP), which involves CÀ H/CÀ H cross-coupling protocols driven by the activation of monomers' C(sp 2 )À H bonds. Furthermore, poly(annulation) via CÀ H bond activation chemistry leads to the formation of unique pi-conjugated moieties as part of the polymeric backbone. This review thus summarises advances to date in the synthesis of conjugated polymers utilizing transition metal catalysed CÀ H bond activation chemistry. A variety of conjugated polymers via DArP including poly(thiophene), thieno [3,4-c]pyrrole-4,6-dione)-containing, fluorenyl-containing, benzothiadiazole-containing and diketopyrrolopyrrolecontaining copolymers, were summarized. Conjugated polymers obtained through Ox-DArP were outlined and compared. Furthermore, poly(annulation) using transition metal catalysed CÀ H bond activation chemistry was also reviewed. In the last part of this review, difficulties and perspective to make use of transition metal catalysed CÀ H activation polymerization to prepare conjugated polymers were discussed and commented.

Survey of Recent Advances in Molecular Fluorophores, Unconjugated Polymers, and Emerging Functional Materials Designed for Electrofluorochromic Use

“…By combining intrinsic fluorophores with electroactive groups, molecular electrofluorochromic materials can be designed to have a high electrofluorochromic performance to enable functioning devices. The advent of readily accessible and diverse synthetic methods such as direct arylation polymerization has resulted in molecular electrofluorochromic materials that cover a wide range of aspects related to structural diversity, and in turn, a range of emission and redox properties [ 121 ]. Although the properties of molecular fluorophores can be tailored, their properties tend to degrade during prolonged device operation.…”

“…Conjugated polymers can similarly be prepared by the step-growth polymerization of difunctionalized complementary monomers via direct arylation polymerization [ 121 , 129 , 130 , 131 , 132 ], Suzuki coupling [ 133 ], and Kumada methods [ 134 ]. Although they can be used as electrochromes, they may not be ideally suited for use as electrofluorochromic materials.…”

Strategies for the synthesis of water-soluble conjugated polymers

“…The main obstacle for using click chemistry in combination with cross-coupling is related to the DHAP. From C-H activation, where the alkyne can be activated instead of the desired aromatic position, poly(annulation) can often happen [87,88]. Thus, if one wishes to use click chemistry in combination with DHAP to obtain water-soluble polymers (for instance, to obtain triazide functionalities), the protection of the alkyne group could be utilized, as well as other polymerization methods that do not require a C-H bond activation.…”

Multifunctional Fluorescent Main-Chain Charged Polyelectrolytes Synthesized by Cascade C–H Activation/Annulation Polymerizations

“…Compared with conventional synthetic strategies, polymerizations developed from organic C–H activation/annulation reactions could readily transform the abundantly existing substrates into diverse fluorescent functional MCCPs with cationic ring-fused heteroaromatics as repeating units (Figure C). Benefiting from the advantages of C–H activation chemistry, C–H activation/annulation polymerizations generally possess a wide monomer scope, high atom economy, excellent functional group tolerance, environmentally friendly, and high reaction efficiency. − Moreover, the use of C–H activation/annulation polymerization for the preparation of polyelectrolytes has no need for further modification after polymerization, which can effectively avoid the formation of structural defects in polymer chains. In addition to the inherent advantages of reactions, the unique cationic ring-fused heteroaromatic structures with multiple substituents in polymer backbones not only can greatly enrich the structural diversity of MCCPs but also could endow the corresponding MCCPs with potentially distinct properties and advanced functionalities, such as high thermal stability, intriguing photosensitivity, and efficient and readily tunable aggregate-state fluorescence.…”