光酸化的に耐性のあるヘプタセンの誘導体の合成のために置換剤効果を利用する
Irvinder Kaur1, Nathan N Stein, Ryan P Kopreski
1Department of Chemistry and Materials Science Program, University of New Hampshire, Durham, New Hampshire 03824-3598, USA.
Journal of the American Chemical Society
|February 27, 2009
まとめ
研究者は,戦略的に大容量の置換物を加えることで,高度に安定したヘプタセンの誘導体を合成しました. この新しい化合物は,光酸化に対する例外的な耐性を発揮し,固体で数週間,溶液で数時間持続します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- マテリアルサイエンス 材料科学
- フォトケミストリー フォトケミストリー
背景:
- ヘプタセンの誘導体は,興味深い電子特性で知られているが,安定性が悪いことが多い.
- 光酸化分解は,ポリサイクル芳香炭化水素の実用的な応用を制限する.
研究 の 目的:
- 強化された光酸化抵抗性を有する新しいヘプタセンの誘導体を合成する.
- ヘプタセンの化合物の安定性を支配する構造-特性関係を調査する.
主な方法:
- 異なる置換パターンを持つ4つの新しいヘプタセンの誘導体の合成.
- 合成された化合物の特徴は,スペクトロスコピーおよび分析技術を用いて記述される.
- 異なる条件下 (固体状態,溶液,光への曝露) の光酸化安定性の評価.
主要な成果:
- 4つのヘプタセンの誘導体が合成され,光酸化抵抗の梯度を示した.
- 特定のアリルチオとステリック置換物を含んだヘプタセンの派生物4は,著しい安定性を示した.
- デリバティブ4は,光と空気への曝露下で,固体として数週間,溶液で数時間持続しました.
- 特徴づけられた誘導体4は,HOMO-LUMOの小さなギャップ1.37 eVを示した.
結論:
- 戦略的な置換剤の配置は,ヘプタセンの誘導体における高光酸化安定性を達成する鍵です.
- 設計されたヘプタセン誘導体4は,ポリサイクル芳香炭化水素の材料安定性における重要な進歩を表しています.
- HOMO-LUMOの小さなギャップは,光電子学的応用の可能性を示唆しています.
関連する概念動画
Photochemical 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
Thermal 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.
Cycloaddition 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.
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
Preparation of Epoxides
Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.

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