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

Although doped poly(3,4‐ethylenedioxythiophene) (PEDOT) is extensively used in electronic devices, their molecular‐weight distributions and inadequately defined structures have hindered the elucidation of their underlying conduction mechanism. In this study, we introduce the simplest discrete oligomer models: EDOT dimer radical cation salts. Single‐crystal structural analyses revealed their one‐dimensional (1D) columnar structures, in which the donors were uniformly stacked. Band calculations identified 1D metallic band structures with a strong intracolumnar orbital interaction (band width W≈1 eV), implying the origin of the high conductivity of doped PEDOT. Interestingly, the salts exhibited semiconducting behavior reminiscent of genuine Mott states as a result of electron–electron repulsion (U) dominant over W. This study realized basic models with tunable W and U to understand the conduction mechanism of doped PEDOT through structural modification in oligomers, including the conjugation length. Shortest oligomer models for doped PEDOT: Single‐crystalline dimer models for doped poly(3,4‐ethylenedioxythiophene) (PEDOT) were developed to understand the underlying conduction mechanism of doped PEDOT. The models exhibited one‐dimensional π‐stacking single‐crystal structures possessing half‐filled band structures with exclusively high intracolumnar orbital interactions, implying the origin of the excellent conductivity of doped PEDOT.