剪切和紫外线诱导的光切换在 stilbenic pi-dimer 晶体中,由可逆 [2 + 2] 循环添加驱动
Jong Won Chung1, Youngmin You, Hyun Sue Huh
1Center for Supra molecular Optoelectronics Materials and Department of Materials Science and Engineering, ENG445, Seoul National University, San 56-1, Shilim-dong, Kwanak-ku, Seoul 151-744, Korea.
Journal of the American Chemical Society
|May 26, 2009
概括
新的三甲基替代的乙烯衍生物表现出可逆的光切换. 机械应力或紫外线诱导光,而化恢复非光状态,证明了固态分子包装控制.
科学领域:
- 材料科学 材料科学 材料科学
- 有机化学 有机化学
- 固态化学 固态化学
背景情况:
- 对于pi-dimer系统来说,不对称的蓝乙烯衍生物正在被探索.
- 三甲基替代剂影响分子包装和特性.
- 可逆光切换是材料科学的一个关键目标.
研究的目的:
- 设计和合成具有三甲基组的不对称的蓝乙烯衍生物.
- 为了研究它们在晶体中形成密集的pi-dimer系统的能力.
- 探索由外部刺激驱动的可逆光调制.
主要方法:
- 合成 (Z) -3-(3',5'-Bis(trifluoromethyl) biphenyl-4-yl)-2-(4'-(trifluoromethyl) biphenyl-4-yl) acrylonitrile (CN(L) -TrFMBE) 和其衍生物的合成.
- 结晶学分析以确定分子包装和分子间相互作用 (C-F...H,C-F...pi).
- 谱学研究 (光) 和外部刺激的应用 (剪切应变,紫外线照射,热).
主要成果:
- CN(L) -TrFMBE衍生物在晶体中形成反平行pi-dimer堆.
- 晶体最初是非光的,但在剪切应变或紫外线照射后变得高度光 (高达24%的量子产量).
- 光切换归因于剪切诱导的pi-模对的横向位移,影响循环加法.
- 可逆切换 ("关闭"状态恢复) 通过热来实现.
结论:
- 在固态材料中开发了一种罕见的高对比度可逆光切换的例子.
- 证明分子包装模式的变化可以控制光.
- 由于可逆光切换,该系统表现出平色和光色反应.
相关概念视频
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.
01:16Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
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
01:16Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
![[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
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.
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.