Hutchison Geoffrey R, Ratner Mark A, Marks Tobin J
Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois 60208-3113, USA.
J Phys Chem B. 2005 Mar 3;109(8):3126-38. doi: 10.1021/jp046579v.
Oxidative doping of extended pi-conjugated polymers and oligomers produces dramatic changes in optical and electrical properties, arising from polaron and soliton-derived midgap states. Despite the great importance of such changes for materials properties, far less is known about the cationic polaron states than about the neutral, semiconducting or insulating, undoped materials. The systematic, multifactor computational analysis of oligoheterocycles such as oligothiophenes, oligofurans, and oligopyrroles presented here affords qualitative and quantitative understanding of the interplay among skeletal substitution pattern, electronic structure, and the effective band gap reduction on p-doping. A simple linear relation is derived for predicting p-doped oligomer and polymer effective band gaps based on those of the neutral oligomers; this relationship confirms the effectiveness of a "fixed band" approximation and explains the counterintuitive increase of the effective band gap on p-doping of many small band gap oligomers. The present analysis also suggests new candidates for transparent conductive polymers and predicts limiting behavior of ionization potential, electron affinity, and other properties for various polyheterocyclic systems. The results yield insight into materials constraints in electrochromic polymers as well as on p- and n-type conductors and semiconductors.
扩展π共轭聚合物和低聚物的氧化掺杂会导致光学和电学性质发生显著变化，这源于极化子和孤子衍生的带隙中间态。尽管这些变化对材料性质非常重要，但与中性、半导体或绝缘的未掺杂材料相比，人们对阳离子极化子态的了解要少得多。本文对低聚噻吩、低聚呋喃和低聚吡咯等低聚杂环进行了系统的多因素计算分析，从而定性和定量地理解了骨架取代模式、电子结构以及p型掺杂时有效带隙减小之间的相互作用。基于中性低聚物的有效带隙，推导出了一个简单的线性关系来预测p型掺杂低聚物和聚合物的有效带隙；这种关系证实了“固定带”近似的有效性，并解释了许多小带隙低聚物在p型掺杂时有效带隙出现的反直觉增加。目前的分析还提出了透明导电聚合物的新候选材料，并预测了各种聚杂环体系的电离势、电子亲和势和其他性质的极限行为。这些结果有助于深入了解电致变色聚合物以及p型和n型导体与半导体中的材料限制。
