Configuration Space Analysis of the Specific Rotation of Helicenes
Configuration Space Analysis of the Specific Rotation of Helicenes
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DOI：
10.1021/acs.jpca.9b01823
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发表时间：
2019-05-23
影响因子：
2.9
通讯作者：
Caricato, Marco
中科院分区：
文献类型：
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作者：
Aharon, Tal;Caricato, Marco
在这项工作中，我们提出了一系列螺旋烯分子的分析，以确定其大比旋的驱动力，[α](ω)，并探讨功能化的影响。分析是在分子轨道（MOs）的构型空间中进行的，它允许我们将[α]（ω）分解为单MO激发的跃迁电偶极子和磁偶极子的分量。我们发现螺旋烯分子的[α]（ω）可以用三组基于磁偶极子相对于螺旋轴的方向的跃迁来描述：平行、正交或倾斜。与螺旋轴平行的磁偶极子的跃迁，对应于电子沿着螺旋体的离域运动，提供了最大的贡献，并决定了[α]（ω）的符号和大小。功能化对[α]（ω）有复杂的影响，这取决于取代基的数量和它们的电子导向强度。此外，我们使用本地化的MOs （Boys和Pipek-Mezey）测试了[alpha]（omega）分解分析。我们表明，局部化方案可能有助于简化[α]（ω）分解的解释，但当电子跃迁涉及相对较小的发色团时，它们最好使用。
In this work, we present an analysis of a series of helicene molecules to determine the driving forces for their large specific rotation, [alpha](omega), and probe the effects of functionalization. The analysis is done in the configuration space of the molecular orbitals (MOs), and it allows us to decompose [alpha](omega) into the component transition electric and magnetic dipoles from single MO excitations. We find that [alpha](omega) for helicene molecules may be described by three sets of transitions based on the orientation of the magnetic dipole with respect to the helical axis: parallel, orthogonal, or tilted. The transitions with the magnetic dipole parallel to the helical axis, corresponding to a delocalized motion of the electron along the body of the helix, provide the largest contributions and determine the sign and magnitude of [alpha](omega). Functionalization has a complex effect on [alpha](omega), which is dependent on the number of substituent groups and their electron directing strength. Furthermore, we test the [alpha](omega), decomposition analysis using localized MOs (Boys and Pipek-Mezey). We show that localization schemes may be useful to simplify the interpretation of the [alpha](omega), decomposition, but they are best used when the electronic transitions involve relatively small chromophoric groups.