Departament d'Enginyeria Química, Escola d'Enginyeria d'Igualada, Universitat Politècnica de Catalunya, Pça Rei 15, Igualada 08700, Spain.
J Phys Chem A. 2012 Jul 19;116(28):7571-83. doi: 10.1021/jp303584b. Epub 2012 Jul 3.
In this article, the extrapolation procedures of π-π* electronic transition energy on π-conjugated oligomers are reexamined. Different models, including the simplest coupled oscillator, the free electron, the Hückel approach, the molecular exciton model, and some specific fitting-functions, are compared using the transition energies derived from theoretical calculations on three thiophene-based oligomer series. Specifically, oligomers of up to 30 repeating units have been considered to include the saturation effects as a function of chain length. The coupled oscillator model of W. Kuhn and the fitting-function of Hirayama are the models that present the better suit on the transition energy interpolation as a function of chain length. Using only the first four oligomers of the series (n = 2 up to 8) yields an estimation of the transition energy on the polymer limit with an average error of ∼1.5%. The vertical and adiabatic ionization potential present a better fit with the Hückel model approach. Finally, implications of the environmental polarity on the electronic properties, molecular geometry, charge distribution, and aromaticity are shortly discussed.
本文重新考察了π-π*电子跃迁能在π共轭寡聚物上的外推程序。使用三种噻吩基寡聚物系列的理论计算得出的跃迁能，比较了不同的模型，包括最简单的耦合振荡器、自由电子、Hückel 方法、分子激子模型和一些特定的拟合函数。具体来说，考虑了多达 30 个重复单元的寡聚物，以包括链长作为函数的饱和效应。W. Kuhn 的耦合振荡器模型和 Hirayama 的拟合函数是作为链长的函数对跃迁能插值表现出更好适用性的模型。仅使用系列中的前四个寡聚物（n = 2 至 8），就可以在聚合物极限上估算跃迁能，平均误差约为 1.5%。垂直和绝热电离势与 Hückel 模型方法有更好的拟合。最后，简要讨论了环境极性对电子性质、分子几何形状、电荷分布和芳香性的影响。
