Lingas Rafael, Charistos Nickolas D, Muñoz-Castro Alvaro
Department of Chemistry Laboratory of Quantum and Computational Chemistry, Aristotle University of Thessaloniki, Thessaloniki, 54 124, Greece.
Grupo de Química Inorgánica y Materiales Moleculares Facultad de Ingeniería, Universidad Autónoma de Chile, El Llano Subercaseaux, 2801, Santiago, Chile.
Chemphyschem. 2021 Apr 19;22(8):741-751. doi: 10.1002/cphc.202100057. Epub 2021 Mar 16.
Dications of cycloparaphenyles ([n]CPPs) are known to exhibit in-plane global aromaticity, contained in a nanobelt structure. Recently synthesized ortho and meta isomers of [n]CPPs break the radial symmetry of π structure incorporating perpendicular oriented π orbitals. Herein we set to explore the aromaticity of neutral and dicationic ortho and meta isomers of [8]CPP by dissecting the induced magnetic field to contributions of the twofold radial/perpendicular π system using delocalized canonical molecular orbitals (CMO), and introducing the natural localized molecular orbitals (NLMO) analysis with DFT methods. The dications sustain a reduced global aromatic character of the radial π system under a perpendicular orientation of the external field which declines from ortho to meta isomer and reinforces local aromaticity of ortho ring while it destroys aromaticity of meta ring. Aromaticity variations are determined by symmetry governed rotational excitations of frontier π orbitals. The parallel orientation reveals a substantial reduction of local aromaticity verified with NICS analysis and electron delocalization indices.
已知环对亚苯基（[n]CPPs）的双阳离子在纳米带结构中呈现面内全局芳香性。最近合成的[n]CPPs的邻位和间位异构体打破了包含垂直取向π轨道的π结构的径向对称性。在此，我们通过使用离域正则分子轨道（CMO）将感应磁场分解为双重径向/垂直π系统的贡献，并引入密度泛函理论（DFT）方法进行自然定域分子轨道（NLMO）分析，来探索[8]CPP中性和双阳离子邻位及间位异构体的芳香性。在外部场垂直取向的情况下，双阳离子的径向π系统的全局芳香特征减弱，从邻位异构体到间位异构体逐渐下降，同时增强了邻位环的局部芳香性，而破坏了间位环的芳香性。芳香性的变化由前沿π轨道的对称控制旋转激发决定。平行取向显示通过核独立化学位移（NICS）分析和电子离域指数验证的局部芳香性大幅降低。
