Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium.
Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, University of Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium.
Molecules. 2018 Jun 1;23(6):1333. doi: 10.3390/molecules23061333.
With their versatile molecular topology and aromaticity, porphyrinoid systems combine remarkable chemistry with interesting photophysical properties and nonlinear optical properties. Hence, the field of application of porphyrinoids is very broad ranging from near-infrared dyes to opto-electronic materials. From previous experimental studies, aromaticity emerges as an important concept in determining the photophysical properties and two-photon absorption cross sections of porphyrinoids. Despite a considerable number of studies on porphyrinoids, few investigate the relationship between aromaticity, UV/vis absorption spectra and nonlinear properties. To assess such structure-property relationships, we performed a computational study focusing on a series of Hückel porphyrinoids to: (i) assess their (anti)aromatic character; (ii) determine the fingerprints of aromaticity on the UV/vis spectra; (iii) evaluate the role of aromaticity on the NLO properties. Using an extensive set of aromaticity descriptors based on energetic, magnetic, structural, reactivity and electronic criteria, the aromaticity of [4+2] π-electron porphyrinoids was evidenced as was the antiaromaticity for [4] π-electron systems. In agreement with previous studies, the absorption spectra of aromatic systems display more intense B and Q bands in comparison to their antiaromatic homologues. The nature of these absorption bands was analyzed in detail in terms of polarization, intensity, splitting and composition. Finally, quantities such as the average polarizability and its anisotropy were found to be larger in aromatic systems, whereas first and second hyperpolarizability are influenced by the interplay between aromaticity, planarity and molecular symmetry. To conclude, aromaticity dictates the photophysical properties in porphyrinoids, whereas it is not the only factor determining the magnitude of NLO properties.
卟啉类化合物具有多功能的分子拓扑结构和芳香性，结合了显著的化学性质、有趣的光物理性质和非线性光学性质。因此，卟啉类化合物的应用领域非常广泛，从近红外染料到光电材料。从以前的实验研究中可以看出，芳香性是决定卟啉类化合物光物理性质和双光子吸收截面的一个重要概念。尽管已经有相当多的关于卟啉类化合物的研究，但很少有研究涉及芳香性、紫外/可见吸收光谱和非线性性质之间的关系。为了评估这种结构-性质关系，我们进行了一项计算研究，重点是一系列 Hückel 卟啉类化合物，以：（i）评估它们的（反）芳香性质；（ii）确定芳香性对紫外/可见光谱的影响；（iii）评估芳香性对 NLO 性质的作用。使用一系列基于能量、磁、结构、反应性和电子标准的芳香性描述符，证明了[4+2]π-电子卟啉类化合物的芳香性以及[4]π-电子系统的反芳香性。与以前的研究一致，芳香体系的吸收光谱显示出比其反芳香同系物更强烈的 B 和 Q 带。这些吸收带的性质从极化、强度、分裂和组成等方面进行了详细分析。最后，发现芳香体系的平均极化率及其各向异性较大，而一阶和二阶超极化率则受到芳香性、平面性和分子对称性相互作用的影响。总之，芳香性决定了卟啉类化合物的光物理性质，而不是决定 NLO 性质大小的唯一因素。
