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非结合和子染色体之间的分子内电子相互作用
Georg Jansen1, Björn Kahlert, Frank-Gerrit Klärner
1Institut für Organische Chemie and Institut für Anorganische Chemie, Universität Duisburg-Essen, 45117 Essen, Germany. georg.jansen@uni-duisburg-essen.de
Journal of the American Chemical Society
|June 5, 2010
概括
合成了具有独特蓝色和色红色颜色的新型分子剪贴. 它们充满活力的颜色来自电子相互作用,而不是通过量子化学计算解释的pi-pi堆叠.
科学领域:
- 有机化学 有机化学
- 摄影化学的使用.
- 计算化学计算化学
背景情况:
- 带有p-基核和芳香侧壁的分子剪贴因其电子和光学特性而引起兴趣.
- 了解这些系统中颜色的起源对于设计新的功能性材料至关重要.
- 以前的研究表明,pi-pi相互作用可能会影响电子特性,但这需要在新的剪贴结构中进一步研究.
研究的目的:
- 合成新型分子剪贴 (1和2) 具有p-金间隔器和烯或烯侧墙.
- 为了研究这些分子剪辑中观察到的颜色和色变化的起源.
- 用计算方法阐明电子属性和光谱特征.
主要方法:
- 通过DDQ氧化基前体合成分子剪贴1和2.
- 紫外线/Vis吸收光谱法,以描述合成化合物的光学特性.
- 量子化学初始计算以建模电子结构和预测光谱行为.
主要成果:
- 新的蓝色和色红色分子剪辑 (1和2) 已成功合成,在可见光谱中显示出广泛的吸收带.
- 与更简单的子结构相比,观察到显著的巴托色变化,表明电子转换发生了变化.
- 计算研究证实,颜色来自n→π*和π→π*激发之间的配置相互作用,涉及分子内电荷转移,而不是通过空间的π-π相互作用.
结论:
- 在合成的分子剪辑中观察到的颜色归因于电子相互作用,特别是子核心和芳香侧壁之间的配置相互作用 (同类结合).
- 量子化学计算准确地预测了实验性UV/Vis光谱,验证了拟议的电子模型.
- 这些发现排除了穿越空间的π-π相互作用作为颜色的主要原因,并提供了设计具有可调光学性质的分子的见解.
相关概念视频
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:17Oxidation of Phenols to Quinones
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.