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01:26Photochemical Electrocyclic Reactions: Stereochemistry
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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
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01:26Thermal and Photochemical Electrocyclic Reactions: Overview
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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.
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02:34Structural Isomerism
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Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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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.
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01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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02:52Stereoisomerism
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Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
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基于可自组合的可逆激发状态转换的结构性化策略 (III) 复合物用于多重刺激响应数据加密
Xiangyu Liu1, Jing Liu2, Danlei Zhu1
1Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University Beijing 100084, P. R. China.
Journal of the American Chemical Society
|October 15, 2024
概括
研究人员开发了一种新方法,使用自我组装来创建刺激响应的 (III) 复合体. 这些材料在不同条件下改变颜色,从而实现多重刺激响应的数据加密.
科学领域:
- 材料科学
- 摄影化学
- 超分子化学
背景情况:
- 响应刺激的染色材料随着外部刺激而改变颜色,并找到广泛的应用.
- 过渡金属复合物,特别是 (III) 复合物,由于由构成和堆叠影响的调节性兴奋状态,对色材料具有前景.
- 在八面体 (III) 复合体中实现有序堆叠,以实现对多重刺激的反应是具有挑战性的.
研究的目的:
- 通过自组装开发结构刚性化策略,用于可逆调节 (III) 复杂激发状态.
- 在数据加密应用的各种刺激下实现 (III) 复合物的颜色切换.
- 克服了八面体 (III) 复合体中有序堆叠的挑战.
主要方法:
- 化 (III) 复合物的制备与化 (Perfluorophenyl) 酸盐 ([B (PhF5) 4]) 反.
- 使用反和 (III) 离子之间的极-π相互作用来诱导自我组装和结构刚性.
- 在聚合状态中,研究从金属到配体电荷转移 (3MLCT) 到配体中心 (3LC) 状态的兴奋状态转换.
主要成果:
- 结构刚性限制了3MLCT激发状态的构造变化,促进了转换到3LC激发状态.
- 激发状态转换导致光发光谱发生54纳米的蓝色变化 (从黄色到天蓝).
- 开发出 (III) 复合体,对低温,蒸汽蒸发和机械力进行数据加密具有明显的反应.
结论:
- 一种新的八面体复合体排列策略得到了成功实施.
- 这项研究为控制过渡金属复杂行为的光物理过程提供了更深入的见解.
- 这项工作为设计先进的多重应激色材料提供了新的视角.