Exciton localization in polymers with static disorder
Exciton localization in polymers with static disorder
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DOI：
10.1103/physrevb.80.165418
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发表时间：
2009-10-01
影响因子：
3.7
通讯作者：
Trembath, David
中科院分区：
文献类型：
--
作者：
Barford, William;Trembath, David
利用共轭聚合物的组态相互作用单粒子计算和映射到单粒子安德森模型，我们研究了热致静态无序对共轭聚合物中激子性质的影响.我们使用聚（对亚苯基）作为一个模型系统，其中的非对角无序产生的扭转角的波动和对角无序产生的波动，在当地的相对介电常数。我们得到以下观察结果和结论：（1）无序使激子局域化。激子局域化长度定义激子共轭长度。(2)激子在空间上随机地沿链沿着定位，其中定位长度通常随着激发能量的增加而增加（直到带中心）。这些定义了定位或缀合片段。通常，共辄区段重叠并且在空间上不是不同的。(3)三重态激子比单重态激子更局域化，因为它们的带宽更小。(4)高斯随机无序的标准偏差σ满足类似于根T的σ，其中T是温度。(5)映射到安德森模型上表明，共轭长度< l >σ< l >在带的边缘处与σ（-2/3）相似，< l >在带的中心处与σ（-3/2）相似。(6)聚（对亚苯基）中扭转角的相关长度按σ（-2）标度。因此，激子共轭长度和构象无序之间没有直接的定量相关性。(7)吸收不均匀谱线宽度的尺度近似为根T。(8)对于聚（对亚苯基）中的无序的实际值< l >，对于最低激发单线态，类似于8个重复单元，并且在吸收最大值处增加到类似于20个重复单元。吸收线宽度近似为0.5 eV。我们使用这些结果得出进一步的结论，在共轭聚合物的电子过程。
Using configuration interaction-singles calculations of realistic models of conjugated polymers and by employing a mapping onto the single-particle Anderson model, we investigate the role of thermally induced static disorder on the properties of excitons in conjugated polymers. We use poly (para-phenylene) as a model system, where the off-diagonal disorder arises from fluctuations in the torsional angles and the diagonal disorder arises from fluctuations in the local relative permittivity. We make the following observations and conclusions: (1) disorder localizes excitons. The exciton localization length defines the exciton conjugation length. (2) Excitons are randomly spatially localized along the chain, with the localization length generally increasing as the excitation energy increases (up to the band center). These define localization or conjugation segments. Generally, the conjugation segments overlap and are not spatially distinct. (3) Triplet excitons are more localized than singlet excitons, because of their smaller band widths. (4) The standard deviation of the Gaussian random disorder, sigma, satisfies sigma similar to root T, where T is the temperature. (5) Mapping onto the Anderson model indicates that the conjugation length, < l >, scales as < l >similar to sigma(-2/3) at the edges of the band and < l >similar to sigma(-3/2) at the center of the band. (6) The correlation length of the torsion angles in poly (para-phenylene) scales as sigma(-2). Thus, there is no direct quantitative correlation between exciton conjugation lengths and conformational disorder. (7) The absorption inhomogeneous line width scales approximately as root T. (8) For realistic values of disorder in poly (para-phenylene) < l >similar to 8 repeat units for the lowest excited singlet and increases to similar to 20 repeat units at the absorption maximum. The absorption line width is similar to 0.5 eV. We use these results to draw further conclusions about electronic processes in conjugated polymers.