Significant Enhancement of the Electrical Conductivity of Conjugated Polymers by Post-Processing Side Chain Removal

Abstract

The processability and electronic properties of conjugated polymers (CPs) have become increasingly important due to the potential of these materials in redox and solid-state devices for a broad range of applications. To solubilize CPs, side chains are needed, but such side chains reduce the relative fraction of electroactive material in the film, potentially obstructing π−π intermolecular interactions, localizing charge carriers, and compromising desirable optoelectronic properties. To reduce the deleterious effects of side chains, we demonstrate that postprocessing side chain removal, exemplified here via ester hydrolysis, significantly increases the electrical conductivity of chemically doped CP films. Beginning with a model system consisting of an ester functionalized ProDOT copolymerized with a dimethylProDOT, we used a variety of methods to assess the changes in polymer film volume and morphology upon hydrolysis and resulting active material densification. Via a combination of electrochemistry, X-ray photoelectron spectroscopy, and charge transport models, we demonstrate that this increase in electrical conductivity is not due to an increase in degree of doping but an increase in charge carrier density and reduction in carrier localization that occurs due to side chain removal. With this improved understanding of side chain hydrolysis, we then apply this method to high-performance ProDOT-alt-EDOT x copolymers. After hydrolysis, these ProDOT-alt-EDOT x copolymers yield exceptional electrical conductivities (∼700 S/cm), outperforming all previously reported oligoether-/glycol-based CP systems. Ultimately, this methodology advances the ability to solution process highly electrically conductive CP films.

Mapping Out the Nonconjugated Organic Radical Conductors via Chemical or Physical Pathways

“…An additional subcategorization within the first group was conceived, where the TEMPO derivatives with hydroxyl and amino groups (hT and nT) are expected to exhibit characteristic phase behavior, in addition to the electron-donating effect that the two functionalities provide owing to the presence of the hydrogen-bonded network ( vide infra ). 28 The second group under investigation includes sterically less hindered nitroxides that have frequently been utilized in the wet chemistry of TEMPO derivatives for alcohol oxidation, 19 , 21 and it includes 2-azaadamantane N -oxyl (AZADO) and 9-azabicyclo[3.3.1]nonane- N -oxyl (ABNO) ( Figure 1 C). Taking advantage of the small-molecular nature, all of the radicals featured a high radical content as compared to the pristine T as an external standard, based on electron spin resonance (ESR) calculation on each TEMPO derivative ( Figure 1 D, and Figures S2–S9 ).…”

“…The series are designed such that there exists a significant difference in the effect of electron-donating or -withdrawing functionality on the active radical site. An additional subcategorization within the first group was conceived, where the TEMPO derivatives with hydroxyl and amino groups (hT and nT) are expected to exhibit characteristic phase behavior, in addition to the electron-donating effect that the two functionalities provide owing to the presence of the hydrogen-bonded network ( vide infra ) . The second group under investigation includes sterically less hindered nitroxides that have frequently been utilized in the wet chemistry of TEMPO derivatives for alcohol oxidation, , and it includes 2-azaadamantane N -oxyl (AZADO) and 9-azabicyclo[3.3.1]­nonane- N -oxyl (ABNO) (Figure C).…”

“…Also, as has been found in conjugated organics, fundamentals established on small-molecular radicals are expected to be readily translated into the designer macromolecular radicals, which altogether will realize high-performance radical electronics in the near future. 23 , 28 Thus, it is of key importance that one establishes a comprehensive understanding of these small-molecular radicals and the context they are in, among relevant subfields of open-shell chemistry.…”

“…The main advantage of such radicals compared to the macromolecular ones is their high radical density owing to the absence of insulating backbone structures, which is beneficial to the electronic performance of the resultant devices. Also, as has been found in conjugated organics, fundamentals established on small-molecular radicals are expected to be readily translated into the designer macromolecular radicals, which altogether will realize high-performance radical electronics in the near future. , Thus, it is of key importance that one establishes a comprehensive understanding of these small-molecular radicals and the context they are in, among relevant subfields of open-shell chemistry.…”

Synthetic Route to Conjugated Donor–Acceptor Polymer Brushes via Alternating Copolymerization of Bifunctional Monomers

“…Moreover, they consist of tangled polymer chains that disturb the energy and/or charge transfer process [31], and a precise arrangement of the active moieties within such films would mimic the natural light-harvesting systems that are highly desired [32]. The electronic properties of casted polymer layers are also obstructed by the presence of side bulky substituents, introduced to provide the solubility of the macromolecules [33]. These undisputed problems could be overcome by the formation of conjugated surface-grafted polymer brushes (PB), whose architecture takes into account the presence of molecular wires connected to the substrate via chemical bonds in a perpendicular orientation with respect to the surface.…”