Craig Ben, Townsend Peter, de Leon Carlos Ponce, Skylaris Chris-Kriton, Kramer Denis
School of Engineering, University of Southampton, University Road, Southampton SO17 1BJ, UK.
Department of Chemistry and Chemical Biology, Rutgers University, 123 Bevier Rd., Piscataway, NJ 08854, USA.
Polymers (Basel). 2024 May 11;16(10):1376. doi: 10.3390/polym16101376.
In this work, we use density functional theory to investigate the electronic structure of poly(3,4-ethylenedioxythiophene) (PEDOT) oligomers with co-located AlCl anions, a promising combination for energy storage. The 1980s bipolaron model remains the dominant interpretation of the electronic structure of PEDOT despite recent theoretical progress that has provided new definitions of bipolarons and polarons. By considering the influence of oligomer length, oxidation or anion concentration and spin state, we find no evidence for many of the assertions of the 1980s bipolaron model and so further contribute to a new understanding. No self-localisation of positive charges in PEDOT is found, as predicted by the bipolaron model at the hybrid functional level. Instead, our results show distortions that exhibit a single or a double peak in bond length alternations and charge density. Either can occur at different oxidation or anion concentrations. Rather than representing bipolarons or polaron pairs in the original model, these are electron distributions driven by a range of factors. Distortions can span an arbitrary number of nearby anions. We also contribute a novel conductivity hypothesis. Conductivity in conducting polymers has been observed to reduce at anion concentrations above 0.5. We show that at high anion concentrations, the energy of the localised, non-bonding anionic orbitals approaches that of the system HOMO due to Coulombic repulsion between anions. We hypothesize that with nucleic motion in the macropolymer, these orbitals will interfere with the hopping of charge carriers between sites of similar energy, lowering conductivity.
在这项工作中，我们使用密度泛函理论研究了与共定位的AlCl阴离子相结合的聚（3,4 - 亚乙基二氧噻吩）（PEDOT）低聚物的电子结构，这是一种很有前景的储能组合。尽管最近的理论进展为双极化子和极化子提供了新的定义，但20世纪80年代的双极化子模型仍然是对PEDOT电子结构的主要解释。通过考虑低聚物长度、氧化或阴离子浓度以及自旋态的影响，我们没有发现20世纪80年代双极化子模型中许多断言的证据，因此进一步推动了新的理解。正如双极化子模型在杂化泛函水平上所预测的那样，在PEDOT中未发现正电荷的自局域化。相反，我们的结果显示出在键长交替和电荷密度中呈现单峰或双峰的畸变。这两种情况都可能在不同的氧化或阴离子浓度下出现。这些畸变不是原始模型中所表示的双极化子或极化子对，而是由一系列因素驱动的电子分布。畸变可以跨越任意数量的相邻阴离子。我们还提出了一个新颖的电导率假设。已观察到导电聚合物中的电导率在阴离子浓度高于0.5时会降低。我们表明，在高阴离子浓度下，由于阴离子之间的库仑排斥，局域化的非键合阴离子轨道的能量接近系统的最高占据分子轨道（HOMO）。我们假设，随着大分子聚合物中的核酸运动，这些轨道将干扰能量相似位点之间电荷载流子的跳跃，从而降低电导率。
