Band-filling effects in single-crystalline oligomer models for doped PEDOT: 3,4-ethylenedioxythiophene (EDOT) dimer salt with hydrogen-bonded infinite sulfate anion chains

Abstract

Band-filling modulation of single-crystalline 3,4-ethylenedioxythiophene dimer salt from the half-filled state based on hydrogen-bonded anion chain formation enhanced the conductivity.

Metallic State of a Mixed-Sequence Oligomer Salt That Models Doped PEDOT Family

“…The transfer integrals (intracolumnar and intercolumnar interactions; t intra and t inter in Figure c) were determined to be 0.0812 and 0.0181 eV for the nearest two intracolumnar and intercolumnar donors, respectively (Figure S17 and Table S3), using the first-principles calculation packages QE , and RESPACK (see Supporting Information for the details). These calculations confirmed the q1D electronic structure, and this is the first time that such an electronic structure has been observed for an oligothiophene conductor. ,,,− This was further validated by calculating the Fermi surfaces, which were typical q1D surfaces with closed pockets (Figure S16a).…”

“…The combined effects of expanded conjugate area and band-filling modulation, as well as the dimensionality of the electronic structure of higher than one, resulted in a room-temperature conductivity (36 S cm –1 ) for the single crystal of 4PS ·(PF 6 ) 1.2 (solvent) m significantly higher than those for the short oligomer salts. To the best of our knowledge, this value is the highest among those of single-crystal oligothiophene conductors. ,,,− Furthermore, electrical resistivity and polarized reflectivity measurements revealed a metallic state above room temperature for the first time among these conductors. Notably, the salt exhibited a change in conductivity behavior at ∼280 K, indicative of a crossover from a metallic to a semiconducting state, accompanied by changes in magnetic behavior.…”

“…The polarized ultraviolet–infrared reflectivity spectra of a single crystal of 4PS ·(PF 6 ) 1.2 (solvent) m with a size of S = 48 μm 2 and L = 300 μm, as well as those of 2O ·PF 6 and 3O ·PF 6 (CH 2 Cl 2 ) l as the references, were obtained at room temperature by applying an electric field along the π-stacking direction. The spectrum of 4PS ·(PF 6 ) 1.2 (solvent) m , which lacked a distinct peak top, unlike those of short oligomer salts, which displayed with peak top energies of 0.72 eV ( 2O ·PF 6 ) and 0.63 eV [ 3O ·PF 6 (CH 2 Cl 2 ) l ] based on Mott gap energies (Figure ). The intensity of the acquired 4PS ·(PF 6 ) 1.2 (solvent) m spectrum increased with decreasing photon energy, indicating the emergence of plasma reflection mainly in the metallic state .…”

“…The packing structure contains spaces that facilitate the incorporation of additional anions, leading to deviation of the band filling from the half-filled state. The combined effects of the expanded conjugate area and band-filling modulation based on the mixed sequence, along with a dimensionality higher than one, significantly increased the σ rt value by five to six orders of magnitude compared to those of short oligomer salts. , To the best of our knowledge, this σ rt value is the highest among those of single-crystalline oligomeric conductors; − ,,− it is even higher than that of doped PEDOT without post-treatment. , Furthermore, a metallic state was observed above room temperature in single-crystalline oligoEDOT systems for the first time. This strategy of precisely controlling electronic structures using mixed sequences is unique to oligomer conductors and has not been demonstrated in low-molecular-weight or polymer-based organic conductor materials.…”

“…Initially, we demonstrated the effects of reducing U eff by (1) elongating the oligomers from a dimer to a trimer [i.e., from 2O ·PF 6 to 3O ·PF 6 (CH 2 Cl 2 ) l in Figure ], and (2) modulating the band filling from the half-filled state (i.e., 2O ·[H y (SO 4 ) z ] δ , δ = − y + 2 z in Figure ). Both approaches efficiently led to higher σ rt (1.0 × 10 –3 to 0.32 S cm –1 ). Additional elongation of oligomers and deviation of their band filling from the half-filled states may further reduce U eff and help achieve metallic states with U eff / W ≤ 1 .…”