Eco-friendly semiconducting polymers: from greener synthesis to greener processability

Abstract

This review presents emerging strategies for materials scientists to design, prepare and process semiconducting polymers in a more sustainable and eco-friendly manner.

Advances in applying C–H functionalization and naturally sourced building blocks in organic semiconductor synthesis

“…Direct arylation and oxidative C-H/C-H coupling are the two C-H activation involved synthetic routes for OSMs as green alternatives to the conventional synthetic methods, such as Suzuki and Stille couplings, due to their high atom economy (Scheme 2). [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] For instance, the atom economy of a Suzuki coupling shown in Scheme 1a is calculated to be 60%. If direct arylation and oxidative C-H/C-H coupling were used instead to synthesize the same organic semiconducting product in Scheme 1a, respectively, then the values of atom economy would be 80% for direct arylation and 99% for oxidative C-H/C-H coupling.…”

“…DArP, as an emerging subject in the field of OSM synthesis, has been reviewed many times in the past few years. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] The semiconducting polymers synthesized via DArP are mostly linear homopolymers and alternating copolymers. When homopolymers are prepared using DArP, the monomer has a C-X (X = Cl, Br, I) bond and a C-H bond to proceed a head-to-tail polycondensation (Scheme 4, top).…”

“…The application of oxidative C-H/C-H coupling towards the OSM synthesis, including small molecule semiconducting materials, semiconducting homopolymers, and D-A copolymers, have been reviewed considerably in the past few years. [29][30][31][32][33][34] D-A alternating copolymers are amongst the most challenging semiconducting poly(arylene)s to synthesize via oxidative C-H/C-H coupling (also referred to as crossdehydrogenative coupling (CDC) in this situation) (Scheme 8a), due to the difficulty in achieving high chemo-and regioselectivities when multiple possible reactive sites, in this case C-H bonds, are present. Moreover, the catalysts often have insufficient selectivity to distinguish the donor and acceptor monomers.…”

“…The organic solvents that are extensively used in the synthesis of OSMs are mostly aprotic solvents, including DMF, toluene, THF, chlorobenzene, etc. 33,34,40,42 These solvents are favored in OSM synthesis not only because of the high solubility of the organic starting materials and semiconducting products in them, but also because solvents such as DMF and DMAc can act as ligands coordinating to the metal complexes in the reactions. 34,38 Unfortunately, these organic solvents are typically highly hazardous to humans and the environment, which makes them unsuitable from an environmental perspective.…”

“…Many scientific endeavors have been made to improve the environmental impact of OSMs, including shortening the synthetic routes by adopting C-H functionalization, applying green solvents, replacing the toxic and scarce metal catalysts with earth abundant (first row) transition metal catalysts, reducing the energy consumption by performing the synthesis under ambient conditions, as well as utilizing naturally sourced building blocks. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] This review highlights the progress on enhancing the environmental friendliness of synthetic protocols, consisting of synthetic routes, reagents, reaction conditions, and building blocks of OSMs, made in the past four years to facilitate the large-scale production and commercialization of OSMs. Specifically, the purification and processing of OSMs are outside the scope of this review.…”