The Simplest Model for Doped Poly(3,4-ethylenedioxythiophene) (PEDOT): Single-crystalline EDOT Dimer Radical Cation Salts

Highly flexible yet strain-insensitive conjugated polymer

Imparting excellent electrical properties, mechanical robustness, suppleness, conduction stability during deformation, and self-healing to intrinsic conducting polymers is a challenging endeavor. The reversibly interlocked macromolecular networks (RILNs) approach is utilized to tackle this problem. Specifically, poly(3,4-ethylenedioxythiophene) (PEDOT) is mixed with flexible polysulfonic acid networks crosslinked by reversible Diels-Alder bonds, while rigid polyaniline networks crosslinked by reversible Schiff base bonds act as molecular staples. Owing to the joint actions of the doping effect of polyaniline on PEDOT, the specific interlocking architecture and synergy between the component materials, the electrical conductivity (59.3-980.5 S cm-1), tensile strength (8.4-81.6 MPa) and elongation at break (44.5-411.0%) of the resultant PEDOT/RILNs films is significantly tunable according to different usage scenarios by adjusting the PEDOT content from 1.48 to 22.24 wt%. More importantly, the electrical resistance of PEDOT/RILNs remains constant during not only a single large extension and deflection but also repeated stretching (up to 1500 cycles) and bending (up to 106 cycles). The built-in reversible covalent bonds enable the PEDOT/RILNs to autonomously restore damaged mechanical and electrical performance. These record-breaking results and the demonstration of self-powered sensor made of PEDOT/RILNs suggest that the proposed approach successfully satisfies various conflicting requirements of flexible electronics regarding the properties of conducting polymers.

Orbital hybridization of donor and acceptor to enhance the conductivity of mixed-stack complexes

Mixed-stack complexes which comprise columns of alternating donors and acceptors are organic conductors with typically poor electrical conductivity because they are either in a neutral or highly ionic state. This indicates that conductive carriers are insufficient or are mainly localized. In this study, mixed-stack complexes that uniquely exist at the neutral-ionic boundary were synthesized by combining donors (bis(3,4-ethylenedichalcogenothiophene)) and acceptors (fluorinated tetracyanoquinodimethanes) with similar energy levels and orbital symmetry between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor. Surprisingly, the orbitals were highly hybridized in the single-crystal complexes, enhancing the room-temperature conductivity (10-4-0.1 S cm-1) of mixed-stack complexes. Specifically, the maximum conductivity was the highest reported for single-crystal mixed-stack complexes under ambient pressures. The unique electronic structures at the neutral-ionic boundary exhibited structural perturbations between their electron-itinerant and localized states, causing abrupt temperature-dependent changes in their electrical, optical, dielectric, and magnetic properties.

Single-crystalline oligomer-based conductors modeling the doped poly(3,4-ethylenedioxythiophene) family

Conductive polymers with highly conjugated systems, such as the doped poly(3,4-ethylenedioxythiophene) (PEDOT) family, are commonly used in organic electronics. However, their structural inhomogeneity with various chain lengths makes it difficult to control their conductivities and structural details. On the other hand, low-molecular-weight materials have well-defined structures but relatively narrow conjugate areas with a limited range of Coulomb repulsion between carriers (Ueff), which hamper the flexible control of conductivities. To bridge this gap, we developed oligomer-based conductors, which are intermediate materials between polymers and low-molecular-weight materials. Using a library of single-crystal charge-transfer salts of oligo(3,4-ethylenedioxythiophene) (oligoEDOT) analogs that model the doped PEDOT family, we have investigated the structure-determining factors affecting their conductivities, such as counter anion variations, lengths of oligomer donor, and band fillings. Through the screening study, we developed oligoEDOT analogs with tunable room temperature conductivities by several orders of magnitude, including a metallic state above room temperature. In this study, we consistently evaluated the electronic structural insights by first-principles calculations and revealed that Ueff is the dominant factor that determines the relationship between the structures and conductivities. The unique features of oligoEDOT conductor systems with widely variable Ueff can differentiate these systems from strongly electron-correlated systems.

Conjugation Length Effect on the Conducting Behavior of Single-crystalline Oligo(3,4-ethylenedioxythiophene) (nEDOT) Radical Cation Salts

The conjugation length is a unique structural factor for oligomer-based π-conjugated conductors as it modulates their electronic structures. Herein, we demonstrated the conjugation length effects on conductivity by comparing a...