Conjugated polymers - Problems and promises

Conjugated polymers (CPs) are unique in their synthetic challenges to tailor their chemical, electronic, and processing properties while identifying significant structure-to-property correlations. Over the past half century chemists have worked towards synthesizing more complex and solution processable conjugated polymers while approaching structural perfection. These efforts aim to maximize their beneficial properties such as high charge mobilities, impressive absorption and emission signals, as well as the ability to stabilize charges, among others. Yet, chemists have only scratched the surface of these characteristics, and new synthetic approaches continue to elevate the field of conjugated polymers. The processability of CPs is no longer solely dependent on adding solubilizing chains to the macromolecules, but can be achieved through polymerizing soluble derivatives that can undergo post-polymerization modification resulting in the desired CPs. New step-growth and chain-growth polymerization techniques have been discovered to provide control over polymerization of CPs to manipulate their molecular weight and molecular weight distribution, in addition to producing new donor-acceptor copolymers that have enhanced electronic and photophysical properties. Additionally, graphene nanoribbons can be synthesized with atomic precision along their edges to control their charge transport properties, and even their ability to create spins along their periphery for potential use in spintronics. New vapor-phase polymerization techniques have made it possible to create thin films of poorly soluble polymers without the need for toxic solvents, and recent breakthroughs in aryl-aryl couplings have eliminated the need for toxic and expensive reagents. Furthermore, strides have been made to bridge electrodes in organic devices with either small molecules or CPs in attempts of achieving single molecule devices, while chemists have also pursued expanding CPs into the second dimension in an effort to improve their charge carrier mobilities. In honor of Staudinger's 100th anniversary of identifying the field of polymer chemistry this article will outline how the synthetic evolution of conjugated polymers has resulted in the aforementioned properties, among others, and how these materials have opened the door for many state-of-the-art applications. (C) 2019 Elsevier B.V. All rights reserved.