Experimental and theoretical investigations of circular dichroism of donor-acceptor 1,1'-binaphthyls : Influence of substitution on the coupling amplitude and cotton effect of the charge-transfer band
Experimental and theoretical investigations of circular dichroism of donor-acceptor 1,1'-binaphthyls : Influence of substitution on the coupling amplitude and cotton effect of the charge-transfer band
复制标题
供体-受体1,1-联萘的圆二色性的实验和理论研究：取代对电荷转移带耦合幅度和棉花效应的影响
作者：
Y.Nakai;M.Nishizaka;C.Yang;G.Fukuhara;T.Mori;Y.Inoue
从理论和实验上研究了给-受体联萘的电子圆二色光谱。合成了对映体纯的1-（2-甲氧基-1-萘基）-和1-（2，3-二甲氧基-1-萘基）-2-甲基异喹啉四氟硼酸盐（DA和D ′ A），比较了它们的紫外-可见光谱和圆二色光谱。供体-受体相互作用从较长波长处的吸收是明显的，而其强度彼此没有很大差异。此外，当用密度泛函理论优化几何构型时，DA和D ′ A中的两个芳香平面得到了非常相似的结构。后者香料中的额外甲氧基几乎不干扰紫外-可见光谱，但显着影响CD光谱。因此，所观察到的CD光谱彼此之间存在相当大的差异，特别是在1B波段的偶联体中，其振幅几乎降低到D ′ A的四分之一。理论研究得到以下结论：（1）DA和D ′ A的1，1 ′-联萘中心C → C二面角势能曲线底部较平坦，在室温下可自由旋转。然而，D ′ A的电位曲线与DA的电位曲线明显不同，DA的电位曲线更陡，并偏向于顺时针。由于所观察到的CD光谱是不同二面角构象的集合，这种势能差异肯定会影响整个光谱;（2）在3-位引入的额外甲氧基有效地改变了CD光谱模式，这在理论上得到了RI-CC2/TZVPP水平上的计算的支持;（3）因此，经典的耦合振子理论，其中仅考虑两个芳香平面的跃迁偶极矩之间的角度，不适用于1的手旋光性质的定量评估，1 ′-联萘;相反，量子化学方法是优选的，允许与实验进行直接比较。Chirality 2011.© 2011 Wiley Periodicals，Inc.
The electronic circular dichroism (CD) spectra of donor–acceptor binaphthyls were investigated experimentally and theoretically. The enantiomerically pure forms of 1‐(2‐methoxy‐1‐naphthyl)‐ and 1‐(2,3‐dimethoxy‐1‐naphthyl)‐2‐methylisoquinolinium tetrafluoroborates (DAandD′A) were prepared, and their UV–vis and CD spectra were compared. The donor–acceptor interaction was apparent from the absorption at longer wavelengths, whereas its strength was not very different from each other. In addition, very similar structures were obtained for the two aromatic planes inDAandD′Awhen the geometry was optimized by the density functional theory. The additional methoxy group in the latter spices scarcely disturbed the UV–vis spectrum but significantly affected the CD spectrum. Thus, the observed CD spectra were considerably different from each other, especially in the1Bbband couplet, where the amplitude was reduced to almost one‐fourth inD′A. The theoretical investigations led to the following conclusions: (1) The potential curve associated with the central CC dihedral angle of 1,1′‐binaphthyl is fairly flat at the bottom for bothDAandD′Aand freely rotating at an ambient temperature. The potential curve ofD′Ais, however, significantly different from that ofDA, in which the curve is much steeper and biased to thes‐cisside. As the observed CD spectrum is an ensemble of conformers of various dihedral angles, such difference in potential certainly affects the overall spectrum; (2) The additional methoxy group introduced at the 3‐position effectively altered the CD spectral pattern, which was theoretically supported by the calculation at the RI‐CC2/TZVPP level; (3) Consequently, the classical coupled oscillator theory, in which the angle between the transition dipole moments of two aromatic planes is solely considered, is not applicable to the quantitative evaluation of the chiroptical properties of 1,1′‐binaphthyls; rather, the quantum chemical approach is preferred, permitting a direct comparison with the experiment. Chirality 2011. © 2011 Wiley Periodicals, Inc.