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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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01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
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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.
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01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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![[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12417.jpg&w=3840&q=75)
01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
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The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
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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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ダイアリエーテンの分子結合における高効率の光スイッチ
Imen Hnid1, Denis Frath1, Frederic Lafolet1
1Université de Paris, ITODYS, CNRS, UMR 7086, 15 rue J-A de Baïf, 75205 Paris Cedex 13, France.
Journal of the American Chemical Society
|April 14, 2020
まとめ
ディアリレチンの薄い層が堆積し,分子結合を形成した. これらの結合は,光誘導によるスイッチングで有意な導電性変化を示し,分子電子学の可能性を実証した.
科学分野:
- 材料科学
- 分子電子
- 有機化学
背景:
- ディアリエーテンのオリゴーマー (oligo(DAE)) は,分子電子学の潜在的応用を持つ光色分子である.
- 分子結合の伝導性を制御することは 装置の開発に不可欠です
研究 の 目的:
- ダリエレタンオリゴマーの薄層を用いて固体分子結合を製造し特徴づけること.
- これらの分子結合の 光伝導性を調べるため
主な方法:
- オリゴ ((DAE) の電気化学的堆積は,ガラスのような炭素と金の電極に.
- 電気化学,XPS,AFMを用いた特徴付け
- C-AFMの先端と異なる層の厚さ (2-3 nmと8-9 nm) を有する分子結合の製造.
主要な成果:
- オリゴ (DAE) 薄層の沈殿と特徴付けに成功した.
- オープン (高度抵抗性) と閉じた (導電性) 形態の間の光誘導の切り替えが実証されている.
- オン/オフ比は3nmのジャンクションで2〜3,9nmのジャンクションで200〜400に達した.
結論:
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