Density functional theory study of neutral and oxidized thiophene oligomers
Density functional theory study of neutral and oxidized thiophene oligomers
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中性和氧化噻吩低聚物的密度泛函理论研究
DOI：
10.1063/1.4829538
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发表时间：
2013-11-14
影响因子：
4.4
通讯作者：
Blaisten-Barojas, Estela
中科院分区：
文献类型：
--
作者：
Dai, Yafei;Wei, Chengwei;Blaisten-Barojas, Estela
采用密度泛函理论（DFT）B3 PW 91/6-311++G（d，p）水平研究了氧化对噻吩（Th）齐聚物的能量和结构的影响.中性n-Th低聚物（2 < n < 13）是平缓弯曲的平面链。电离势和电子亲合势的结果表明，随着n-Th寡聚体链长的增加，它们更容易被氧化。在12-Th中，+2、+4、+6和+8的氧化态是能量稳定的。氧化后，12-Th的共轭骨架从延伸的苯型相切换到醌型相，定位在沿链沿着规则间隔的单体基团上。12-Th的+2、+4、+6和+8氧化态显示出两个位于其链端的+1e，这仅仅是因为链的有限尺寸。在12-Th中，这种末端效应延伸到两个末端单体上，形成正-负电荷二重态。这种特殊的电荷局域化使得n-Th低聚物不同于其他具有类似结构的导电聚合物，如聚吡咯。氧化态12-Th的单电子分子态的光谱显示出在HOMO-LUMO能隙中每+2氧化态两个局部单电子态。低聚噻吩12-Th与F原子以1：2的浓度掺杂呈现出从低聚物到掺杂剂的3.4e的电荷转移，在溶剂存在下增加到4.8e。这些F掺杂低聚物中的电荷分布类似于12-Th的+4氧化态。据预测，掺杂剂产生增强的电荷转移本地化在它们的位置附近，增强在低聚物链的中心部分的双极化子的形成。(C)2013 AIP Publishing LLC.
The effect of oxidation on the energetics and structure of thiophene (Th) oligomers is studied with density functional theory at the B3PW91/6-311++G(d,p) level. Neutral n-Th oligomers (2 < n < 13) are gently curved planar chains. Ionization potential and electron affinity results show that n-Th oligomers are easier to be oxidized as their chain length increases. Oxidation states +2, +4, +6, and +8 are energetically stable in 12-Th. Upon oxidation the conjugated backbone of 12-Th switches from extended benzenoid phase to quinoid phase localized on groups of monomers regularly spaced along the chain. Oxidized states +2, +4, +6, and +8 of 12-Th display two +1e localized at the ends of their chains only because of the finite size of the chains. In 12-Th this end-effect extends over the two terminal monomers forming a positive-negative charge duet. This peculiar charge localization makes n-Th oligomers different from other conducting polymers with similar structure, such as polypyrrole. The spectrum of single-electron molecular states of oxidized 12-Th displays two localized single-electron states in the HOMO-LUMO energy gap per +2 oxidation state. Oligothiophene 12-Th doped with F atoms at 1:2 concentration presents a charge transfer of 3.4 e from oligomer to dopants that increases to 4.8 e in the presence of solvent. The charge distribution in these F-doped oligomers is similar to the +4 oxidation state of 12-Th. It is predicted that dopants produce an enhanced charge transfer localized in the proximity of their locations enhancing the formation of bipolarons in the central part of the oligomer chain. (C) 2013 AIP Publishing LLC.