在聚合物矩阵中,二甲单个分子的光色化
Tuyoshi Fukaminato1, Tohru Umemoto, Yasuhide Iwata
1Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan.
Journal of the American Chemical Society
|April 17, 2007
概括
光光交换分子在刚性聚合物中表现出独特的行为,偏离了典型的指数分布. 这表明受聚合物矩阵环境影响的光子依赖反应机制.
科学领域:
- 材料科学 材料科学 材料科学
- 摄影化学的使用.
- 单分子光谱学 单分子光谱学
背景情况:
- 光交换分子结合了光单元 (二氧化) 和交换单元 (二乙烯).
- 了解它们在不同聚合物矩阵中的行为对于应用至关重要.
研究的目的:
- 研究新型光交换分子的单分子光色反应.
- 分析聚合物矩阵刚度对分子切换动态的影响.
主要方法:
- 准备烯二氧化物-二利乙烯光交换分子.
- 在各种聚合物矩阵 (Zeonex,PMMA,PNBMA) 中进行单分子光测量.
- 光灯启/关时间分布的分析.
主要成果:
- 光灯启/关时间偏离了刚性聚合物 (Zeonex,PMMA) 的指数分布,显示了峰值.
- 在软聚合物 (PnBMA) 中观察到指数分布.
- 异常分布表明量子产量不稳定和光子依赖反应.
结论:
- 聚合物矩阵显著影响光交换动态.
- 一个多局部最小值模型解释了对分子切换的观察到的环境影响.
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
01:12Cycloaddition 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.
01:29UV–Vis Spectroscopy: Woodward–Fieser Rules
UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
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.
01:32UV–Vis Spectroscopy of Conjugated Systems
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in the...
One of the factors influencing λmax is the extent of conjugation in the...
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.