五中替代效应:控制HOMO-LUMO间隙和光氧化电阻
Irvinder Kaur1, Wenling Jia, 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
|November 14, 2008
概括
酸酸衍生物对光氧化具有最大的抗性,并保持小的HOMO-LUMO间隙,为有机电子产品提供更好的稳定性. 这些发现挑战了关于乙烯替代五烯的常见假设.
科学领域:
- 有机化学 有机化学
- 材料科学 材料科学 材料科学
- 物理化学 物理化学
背景情况:
- 五烯衍生物在有机电子产品中至关重要,但它们在操作条件下的稳定性是一个关键的限制.
- 了解分子结构和光氧化稳定性之间的关系对于设计改进的有机半导体至关重要.
研究的目的:
- 量化评估各种替代的五烯衍生物的光氧化抵抗和HOMO-LUMO差距.
- 调查不同替代剂 (素,,乙烯,醇) 和它们对五烯稳定性的影响.
- 为有机电子应用开发更持久和可溶液处理的太烯衍生物提供见解.
主要方法:
- 六种新的和六种已知的五烯衍生物的合成和表征.
- 在相同条件下对光氧化降解的动力学研究.
- 对结构和HOMO-LUMO能量进行计算 (B3LYP/6-311+G**//PM3).
- 对光学和电化学HOMO-LUMO间隙进行实验测量.
主要成果:
- 光氧化阻力受到固体效应,电子性质和替代物位置的影响.
- 乙烯替代的五烯 (例如,TIPS-pentacene) 具有小的HOMO-LUMO差距,但不是最稳定的.
- 一种特定的化和化五烯衍生物比TIPS-pentacene更长寿.
- 基和基替代的五烯表现出最高的光氧化阻力和良好的溶解性.
结论:
- 在研究的衍生品中,化五是对光氧化最坚固的.
- 替代剂的类型,位置和固态/电子因素共同决定了太烯的稳定性.
- 高持久性和可溶性乙烯衍生物对有机场效应晶体管 (OFET) 和有机发光二极管 (OLED) 具有显著的潜力.
相关概念视频
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
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.
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.
Directing and Steric Effects in Disubstituted Benzene Derivatives
When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the more strongly...
Directing Effect of Substituents: meta-Directing Groups
Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the ortho, meta, and para...
Directing Effect of Substituents: ortho–para-Directing Groups
Ortho–para directors are substituent groups attached to the benzene ring and direct the addition of an electrophile to the positions ortho or para to the substituent. All electron-donating groups are considered ortho–para directors. They donate electrons to the ring and make the ring more electron-rich. The ring is therefore susceptible to the addition of electrophiles. Substituents such as amino, hydroxy, or alkoxy, containing lone pairs on the atom adjacent to the ring, donate electrons...
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