Comparative Computational Study of Electronic Excitations of Neutral and Charged Small Oligothiophenes and Their Extrapolations Based on Simple Models
Comparative Computational Study of Electronic Excitations of Neutral and Charged Small Oligothiophenes and Their Extrapolations Based on Simple Models
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DOI：
10.1021/acsomega.8b02972
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发表时间：
2019-03-01
期刊：
影响因子：
4.1
通讯作者：
Jang, Seogjoo J.
中科院分区：
文献类型：
--
作者：
Kowalczyk, Marta;Chen, Ning;Jang, Seogjoo J.
本文报道了用半经验含时密度泛函理论（TD-DFT）方法计算了重复单元n = 2-6的中性和带电低聚噻吩（OTn）的电子激发能。更具体地说，对于OTn，OTn+，和OTn-，我们计算了垂直跃迁能量的电子吸收光谱采用Zerner的版本的中间忽略差分重叠方法的结构优化的PM 6半经验方法和TD-DFT方法与三个不同的泛函，B3 LYP，BVP 86，和M06-2X，结构优化的基态DFT方法，采用相同的泛函。我们还计算了垂直跃迁能量的发射光谱从最低的单重激发态采用TD-DFT方法优化的最低单重激发态的结构。除了真空中的计算结果外，还报道了在极化连续模型水平上计算的溶液相数据，并与现有的实验数据进行了比较。大部分的数据拟合合理，以及由两个简单的模型函数，一个基于Frenkel激子理论和其他的基础上的模型的独立电子在一个盒子中的正弦调制的潜力。尽管相似的拟合性能水平，这两个模型产生明显不同的渐近值的激发能。这些与现有的实验和计算数据的比较表明，激子模型的基础上的值，而似乎高估，更接近真实值比那些基于其他模型。通过对较大低聚物的额外计算证实了该评估。拟合参数提供了新的手段来了解电子激发的OT和它们的尺寸之间的关系，并建议构建简单的粗粒度的激子浴模型适用于聚集体的OT的可行性。
This work reports electronic excitation energies of neutral and charged oligothiophenes (OTn) with repeat unit n = 2-6 computed by routinely used semiempirical and time-dependent density functional theory (TD-DFT) methods. More specifically, for OTn, OTn+, and OTn-, we calculated vertical transition energies for electronic absorption spectroscopy employing the Zerner's version of intermediate neglect differential overlap method for structures optimized by the PM6 semiempirical method and the TD-DFT method with three different functionals, B3LYP, BVP86, and M06-2X, for structures optimized by the ground-state DFT method employing the same functionals. We also calculated vertical transition energies for the emission spectroscopy from the lowest singlet excited states by employing the TD-DFT method for the structures optimized for the lowest singlet excited states. In addition to computational results in vacuum, solution phase data calculated at the level of polarizable continuum model are reported and compared with available experimental data. Most of the data are fitted reasonably well by two simple model functions, one based on a Frenkel exciton theory and the other based on the model of independent electrons in a box with sinusoidal modulation of potential. Despite similar levels of fitting performance, the two models produce distinctively different asymptotic values of excitation energies. Comparison of these with available experimental and computational data suggests that the values based on the exciton model, while seemingly overestimating, are closer to true values than those based on the other model. This assessment is confirmed by additional calculations for a larger oligomer. The fitting parameters offer new means to understand the relationship between electronic excitations of OTs and their sizes and suggest the feasibility of constructing simple coarse-grained exciton-bath models applicable for aggregates of OTs.