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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quantum Chemical Study on the Circular Dichroism Spectra and Specific Rotation of Donor-Acceptor Cyclophanes
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Quantum Chemical Study on the Circular Dichroism Spectra and Specific Rotation of Donor-Acceptor Cyclophanes

机译：供体-受体环的环二色性光谱和比旋光度的量子化学研究

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The structures of donor,acceptor-substituted cyclophanes were optimized by DFT and MP2 methods and compared with the X-ray crystallographic structures.The electronic circular dichroism (CD) spectra of these chiral cyclophanes were simulated by time dependent density functional theory (TD-DFT) with several functionals including different amounts of "exact" Hartree-Fock exchange.The experimental oscillator and rotatory strengths were best reproduced by the BH-LYP/TZV2P method.The specific rotation and vibrational circular dichroism (VCD) spectra were also calculated at the BH-LYP/aug-cc-pVDZ and B3-LYP/6-31G(d) levels,respectively,and compared with the experimental data.Better performance was obtained with the ECD,rather than the specific rotation or the VCD spectral calculations in view of the computation time and accuracy for the determination of absolute configuration (AC).The exciton coupling model can be applied only for the cyclophanes without CT-character.However,the split pattern found in the experiment does not appear to originate from a simple two-transition coupling,indicating that this method should be applied with caution to the AC determination.This conclusion was supported by the TD-DFT investigations of the transition moments and the roles of excited-state electronic configuration associated with these split bands.Cyclophanes with donor-acceptor interactions showed Cotton effects at the CT band and couplets at the 1L_a and 1L_b bands.Although the degree of charge transfer between the rings is very small,as revealed by a Mulliken- Hash analysis,the split Cotton effects are due to a large separation in energy of the donor and acceptor orbitals.The effect of the distance and angle between the donor and acceptor moieties in model (intermolecular) CT complexes on the calculated CD spectra was also studied and compared with those obtained for various paracyclophanes.
机译：用DFT和MP2方法优化了供体，受体取代的环烷的结构，并与X射线晶体结构进行了比较。利用时变密度泛函理论（TD-DFT）模拟了这些手性环烷的电子圆二色光谱。 ），并具有多种功能，其中包括不同数量的“精确” Hartree-Fock交换。通过BH-LYP / TZV2P方法可以最好地再现实验的振荡器和旋转强度。还可以通过计算BHC-LYP / TZV2P的比旋光和振动圆二色性（VCD）光谱分别将BH-LYP / aug-cc-pVDZ和B3-LYP / 6-31G（d）水平与实验数据进行比较。使用ECD可获得更好的性能，而不是比旋光度或VCD光谱计算考虑了确定绝对构型（AC）的计算时间和准确性。激子耦合模型仅适用于不带CT特性的环烷。在实验中发现的似乎不是源自简单的两跃迁耦合，这表明该方法应谨慎用于交流电测定。这一结论得到了跃迁矩和激发作用的TD-DFT研究的支持。与这些分裂带相关的状态电子构型。具有供体-受体相互作用的环环烷在CT带表现出棉花效应，在1L_a和1L_b表现出对联。尽管环之间的电荷转移程度很小，如Mulliken所揭示。 -哈希分析，分裂的棉花效应是由于供体和受体轨道能量的较大分离所致。模型（分子间）CT络合物中供体和受体部分之间的距离和角度对计算的CD光谱的影响也是进行了研究，并与各种副环烷获得的结果进行了比较。

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