Flores Paola, Guadarrama Patricia, Ramos Estrella, Fomine Serguei
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, CU, Coyoacán, México DF 04510, México.
J Phys Chem A. 2008 May 1;112(17):3996-4003. doi: 10.1021/jp710654k. Epub 2008 Mar 18.
The geometries of neutral, mono-, and dioxidized tubular aggregates of cyclo[8]thiophenes containing up to 5 repeating units were fully optimized at the MPWB1K/3-21G* level of theory. Calculated interplane distances between macrocycles were found to be close to 3.1 A for neutral and charged aggregates. The binding energies between macrocycles in neutral intermediates were in the range of 40-45 kcal/mol, increasing for monocations and dropping strongly for dicationic species due to electrostatic repulsion between polarons. It was established that there exists a noticeable interaction between pi-orbitals of individual macrocycles in tubular aggregates as follows from decreasing of the band gap with a number of repeating units in aggregates and the polaron delocalization toward tube axes in oxidized species. A polaron pair is the most stable dicationic state for all studied molecules according to the calculations. A singlet polaron pair is more stable than a triplet one. The energy difference between singlet and triplet states is growing smaller with the size of the system, becoming zero for the pentamer corresponding to a completely dissociated bipolaron.
在MPWB1K/3 - 21G*理论水平下，对含有多达5个重复单元的环[8]噻吩的中性、单氧化和二氧化的管状聚集体的几何结构进行了完全优化。对于中性和带电聚集体，发现大环之间计算出的平面间距接近3.1埃。中性中间体中大环之间的结合能在40 - 45千卡/摩尔范围内，单阳离子的结合能增加，而双阳离子物种由于极化子之间的静电排斥作用结合能大幅下降。研究表明，管状聚集体中各个大环的π轨道之间存在明显的相互作用，这表现为随着聚集体中重复单元数量的增加带隙减小，以及氧化态物种中极化子向管轴的离域。根据计算，极化子对是所有研究分子最稳定的双阳离子状态。单重态极化子对比三重态更稳定。单重态和三重态之间的能量差随着系统尺寸的增大而减小，对于对应于完全解离双极化子的五聚体，该能量差变为零。
