Conducting Polymers Forward
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editorial Conducting polymers forward Twenty years after the Nobel Prize in Chemistry for the discovery of conducting polymers, we refect on the open research questions and the status of commercial development of these materials. ften, in science, breakthroughs in this issue, Scott Keene and collaborators happen by making the most of showed that the electronic output of a Omistakes. A good example of this neuromorphic device made from an is Hideki Shirakawa, Alan MacDiarmid ion-responsive conjugated polymer can and Alan Heeger’s discovery that organic be controlled by the dopamine released polymers are able to transport electric by cells cultured on the polymer, realizing current1, which led to them sharing the 2000 a biohybrid synaptic connection. Ionic– Nobel Prize in Chemistry2. electronic interactions, however, further According to Shirakawa’s recount, in complicate the understanding of these their studies on acetylene polymerization materials: as recently examined by Jonathan he and his collaborator Hyung Chick Pyun Rivnay and colleagues6, ionic–electronic accidentally used a concentration of catalysts injection, transport and coupling play an that was a thousand times too high, obtaining Impact of iodine vapours on the conductivity of important role in the behaviour of organic a silver film composed of crystalline fibres. polyacetylene. Reproduced from ref. 1, RSC. mixed ionic–electronic conductors. Shirakawa continued to experiment on the In the race for materials commerciali- chemistry of polyacetylene films, trying to zation, researchers have explored application transform them into graphite by exposure semiconductors could be used in transistors spaces where the combination of good to halogen vapours — he paid less attention, and even emit light through charge injection4 electrical and mechanical properties, though, to what was happening to their further boosted research in the field, as well as the versatile processability of electrical properties. MacDiarmid, who met prompting the synthesis of polymers with conducting polymers, could be a winner. Shirakawa at a seminar in Tokyo, invited him tailored optoelectronic properties. A few of Antistatic coatings, organic light-emitting to the University of Pennsylvania to perform these materials are now produced at scale panels, flexible photovoltaic modules and those experiments with Heeger. Together, and used in various applications, yet the path organic thin-film transistors are some of they observed a conductivity increase by to commercial success is narrow. As Guo the applications that have gone far along various orders of magnitude (pictured), and Facchetti highlight, the polymerization, the commercialization path. The mixed which marked the official entrance of isolation and purification processes adopted, ionic–electronic conduction properties conjugated polymers into the realm of the cost of monomers and reagents, and of some conducting polymers are used conducting materials. The journey from the management of toxic by-products in electrochromic devices, and their that lucky accident to current research and are all factors determining the economic biocompatibility may prove advantageous in commercialization efforts of semiconducting competitiveness of these materials. Equally other areas such as implantable bioelectronics, and highly conducting polymers is described important is compatibility with industrial biochemical sensing and health monitoring. by Xugang Guo and Antonio Facchetti in a manufacturing processes, which further The discovery of electrical conductivity Comment in this issue. imposes restrictions on the solvents used, has endowed conjugated polymers with In the years following the initial their rheological properties and shelf stability. incredible appeal. Once mainly a playground discovery, the investigation of the Plenty is still unknown about the for chemists, materials scientists and process mechanisms leading to this increased properties of conjugated polymers, in engineers, they are now one of the preferred conductivity continued. The halogenation particular regarding charge transport materials of investigation for physicists, process that the trio performed was an and how it is affected by the polymer electronic engineers, bioengineers and example of p-doping: halogens oxidize the morphology. Charge motion is very fast more. We look forward to seeing whether polyacetylene chains by extracting electrons, along the backbone of a polymer chain, such collaborations will lead to new which leaves positive charges free to move yet it slows down when charges hop breakthroughs, and possibly new Nobel under an applied electric field. Small between neighbouring chains, as Henning prizes. ❐ molecules, too, proved to be effective in Sirringhaus and colleagues described in a 5 oxidizing or reducing the polymer chains recent Review . Torsion and folding of the Published online: 20 August 2020 and making them transport positive or chains, changes in crystallinity and other https://doi.org/10.1038/s41563-020-0792-7 negative charges, respectively. Alternative forms of static and dynamic disorder impact doping processes, such as the use of acids the way charges travel and the mobility References to protonate the polymers backbone, have achieved in organic semiconductors. 1. Shirakawa, H., Louis, E. J., MacDiarmid, A. G., Chiang, C. K. & been developed, and recent studies have Yet some degree of disorder in Heeger, A. J. J. Chem. Soc. Chem. Commun. 578–580 (1977). also shown that charges can be directly polymer films can be beneficial, as it helps 2. Te Nobel Prize in Chemistry, 2000: Conductive Polymers (Nobel transferred between neutral polymers3. penetration of dopant molecules and Committee, 2000); https://www.nobelprize.org/uploads/2018/06/ advanced-chemistryprize2000.pdf A better understanding of the connections other ionic species. Polymers are indeed 3. Xu, K. et al. Nat. Mater. 19, 738–744 (2020). between molecular and electronic structure not only electronic conductors; they can 4. Burroughes, J. H. et al. Nature 347, 539–541 (1990). allowed chemists to synthesize undoped also transport ions that, importantly, can 5. Fratini, S., Nikolka, M., Salleo, A., Schweicher, G. & Sirringhaus, H. Nat. Mater. 19, 491–502 (2020). polymers with semiconducting properties. modulate the electronic behaviour of the 6. Paulsen, B. D., Tybrandt, K., Stavrinidou, E. & Rivnay, J. The demonstration that these organic material. For example, in a Letter published Nat. Mater. 19, 13–26 (2020). NATURE MATERIALS | VOL 19 | SEPTEMBER 2020 | 921 | www.nature.com/naturematerials 921.