Controlled synthesis of conjugated polymers with functional side chains is of great importance, affording welldefined optoelectronic materials possessing enhanced stability and tunability as compared to their alkyl-substituted counterparts. Herein, a chain-growth Suzuki polycondensation of an ester-functionalized thiophene is described using commercially available nickel precatalysts. Model compound studies were used to identify suitable catalysts, and these experiments provided guidance for the polymerization of the ester-substituted monomer. This is the first report of nickel-catalyzed Suzuki cross-coupling for catalyst-transfer polycondensation, and to further illustrate the versatility of this method, block and alternating copolymers with 3-hexylthiophene were synthesized. The presented protocol should serve as an entry point into the synthesis of other electron-deficient polymers and donor−acceptor copolymers with controlled molecular weights and low dispersity.

Periodic π-conjugated polymers of the group 16 heterocycles (furan, thiophene, and selenophene) were synthesized with controlled chain lengths and relatively low dispersities using catalyst-transfer polycondensation. The optical gap and redox potentials of these copolymers were fine-tuned by altering the heterocycle sequence, and atomic force microscopy revealed nanofibrillar morphologies for all the materials. Grazing incidence wide-angle X-ray scattering of the thiophene-selenophene copolymers indicated that the π-stacking distance increased with incorporation of the larger heteroatom (from ∼3.7-4.0 Å), while the lamellar spacing decreased (from ∼15.8-15.2 Å). The study also revealed that periodic sequences allow electronic properties to be tuned while retaining nanofibrillar morphologies similar to those observed for poly(3-hexylthiophene).

There is intense interest in the rational design of semiconducting materials to improve organic electronics. Furan is a particularly attractive monomer for building biorenewable and biodegradable π-conjugated frameworks. In this report, regioregular head-to-tail and head-to-head poly­(3-hexylfuran) were synthesized using chain-growth polycondensation. The resultant polyfurans have relatively low molecular weights but also low dispersities. The head-to-head polyfuran adopted a nearly identical coplanar backbone conformation as its head-to-tail analog in the solid state, as determined by UV–visible spectroscopy and atomic force microscopy. Extensive aggregation of the furan homopolymer during polymerization led to the investigation of an alternating furan-thiophene copolymer, confirming that furyl-based monomers can polymerize in a chain-growth manner. All of the synthesized polymers are sensitive when exposed to both oxygen and light.

This report describes the design and synthesis of a new class of polyfurans bearing ester side chains. The macromolecules can be synthesized using catalyst-transfer polycondensation, providing precise control over molecular weight and molecular weight distribution. Such obtained furan ester polymers are significantly more photostable than their alkyl analogues owing to the electron-withdrawing nature of the attached subunit. Most interestingly, they spontaneously fold into a compact π-stacked helix, yielding a complex multilayer cylindrical nanoparticle with a hollow, rigid, conjugated core composed of the polyfuran backbone and a soft, insulating outer layer formed by the ester side chains. The length of polymer side chains dictates the outer diameter of such nanoparticles, which for the hexyl ester groups used in the present study is equal to ∼2.3 nm. The inner cavity of the conjugated core is lined with oxygen atoms, which set its effective diameter to 0.4 nm. Furthermore, installation of bulkier, branched chiral ester side chains on the repeat unit yields structures that, upon change of solvent, can reversibly transition between an ordered chiral helical folded and disordered unfolded state.

The alternative polymer featuring sustainable furan units were reported for organic photovoltaics with systematic investigation in its morphology.