Adkins Erin M, Miller J Houston
Department of Chemistry George Washington University 800 22nd St, NW Suite 4000, Washington, DC 20052, USA.
Phys Chem Chem Phys. 2017 Oct 25;19(41):28458-28469. doi: 10.1039/c7cp06048c.
Trends linking the topological characteristics of polynuclear aromatic hydrocarbons (PAH) to their electronic properties are reported. TD-DFT electronic spectra computations, using the 6-31G* basis set and B3LYP exchange correlation functional, were calculated for a series of PAH, allowing for the HOMO-LUMO gaps to be reported. Clar structures provide an avenue to link the physical structure and the aromaticity of the molecule; which, when extended by bond length and harmonic oscillator model of aromaticity analysis, provide powerful tools to understand the link between electronic and physical structure. These results lead to the conclusion that all PAH structures show a decrease in HOMO-LUMO gap as a function of size, but the rate of that decrease is directly related to the topology of the molecules. A PAH taxonomy was developed that categorizes PAH into categories with similar topological properties, which allows for modelling of changes in the HOMO-LUMO gap with PAH size. An atom-pair minimization algorithm was used to calculate the binding energy (BE) of homogeneous dimers of the studied PAH. The BE per carbon atom increases with the overall size of the structure to an asymptotic limit, but as with the HOMO-LUMO gap, topology plays a critical secondary factor. Previously published, experimentally determined optical band gaps (OBG) from Tauc/Davis-Mott analysis of extinction spectra in various laminar, non-premixed flames produced a correlation between the HOMO-LUMO gaps of high-symmetry, nearly circular D symmetry molecules to molecular size. The work presented here provides a much more nuanced and predictive evaluation of how OBG depends on structure and size.
报道了将多环芳烃（PAH）的拓扑特征与其电子性质联系起来的趋势。使用6-31G*基组和B3LYP交换相关泛函对一系列PAH进行了TD-DFT电子光谱计算，从而报告了最高占据分子轨道（HOMO）-最低未占据分子轨道（LUMO）能隙。克拉尔结构为连接分子的物理结构和芳香性提供了一条途径；当通过键长和芳香性分析的谐振子模型进行扩展时，它提供了强大的工具来理解电子结构与物理结构之间的联系。这些结果得出的结论是：所有PAH结构的HOMO-LUMO能隙都随尺寸减小，但减小速率与分子的拓扑结构直接相关。开发了一种PAH分类法，将PAH分类为具有相似拓扑性质的类别，这使得能够对HOMO-LUMO能隙随PAH尺寸的变化进行建模。使用原子对最小化算法计算所研究PAH均匀二聚体的结合能（BE）。每个碳原子的BE随结构的整体尺寸增加到一个渐近极限，但与HOMO-LUMO能隙一样，拓扑结构起着关键的次要作用。先前发表的通过对各种层流、非预混火焰中消光光谱进行陶克/戴维斯-莫特分析实验测定的光学带隙（OBG），得出了高对称性、近似圆形D对称性分子的HOMO-LUMO能隙与分子尺寸之间的相关性。本文所呈现的工作对OBG如何依赖于结构和尺寸提供了更为细致入微和具有预测性的评估。
