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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photophysical studies of the trans to cis isomerization of the push-pull molecule: 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene (mepepy)
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Photophysical studies of the trans to cis isomerization of the push-pull molecule: 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene (mepepy)

机译：推挽分子反式至顺式异构化的光物理研究：1-（吡啶-4-基）-2-（N-甲基吡咯-2-基）乙烯（甲基）

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Organic molecules possessing intrarnolecellar charge-transfer properties (D-pi-A type molecules) are of key interest particularly in the development of new optoelectronic materials as well as photoinduced magnetism. One such class of D-pi-A molecules that is of particular interest contains photoswitchable intramolecular charge-transfer states via a photoisomerizable pi-system linking the donor and acceptor groups. Here we report the photophysical and electronic properties of the trans to cis isomerization of 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene ligand (mepepy) in aqueous solution using photoacoustic calorimetry (PAC) and theoretical methods. Density functional theory (DFT) calculations demonstrate a global energy difference between cis and trans isomers of mepepy to be 8 kcal mol(-1), while a slightly lower energy is observed between the local minima for the trans and cis isomers (7 kcal mol(-1)). Interestingly, the trans isomer appears to exhibit two ground-state minima separated by in energy barrier of similar to 9 kcal mol(-1). Results from the PAC Studies indicate that the trans to cis isomerization results in a negligible volume change (0.9 +/- 0.4 mL mol(-1)) and an enthalpy change of 18 +/- 3 kcal mol(-1). The fact that the acoustic waves associated with the trans to cis transition of mepepy overlap in frequency with those of a calorimetric reference implies that the conformational transition occurs faster than the similar to 50 ns response time of the acoustic detector. Comparison of the experimental results with theoretical studies provide evidence for a mechanism in which the trans to cis isomerization of mepepy results in the loss of a hydrogen bond between a water molecule and the pyridine ring of mepepy.
机译：具有核内蜂窝电荷转移特性的有机分子（D-pi-A型分子）尤其在开发新的光电材料以及光致磁性方面引起了人们的极大兴趣。一类特别令人关注的D-pi-A分子通过连接供体和受体基团的可光异构化的pi系统包含光可转换的分子内电荷转移状态。在这里我们报告使用光声热法（PAC）在水溶液中的1-（吡啶-4-基）-2-（N-甲基吡咯-2-基）乙烯配体（pepepy）的反式到顺式异构化的光物理和电子性质和理论方法。密度泛函理论（DFT）计算表明，Mepepy的顺式和反式异构体之间的全局能量差为8 kcal mol（-1），而反式和顺式异构体的局部最小值之间的全局能量差为7 kcal mol（-1） （-1））。有趣的是，反式异构体似乎表现出两个基态最小值，它们被类似于9 kcal mol（-1）的能垒隔开。 PAC研究的结果表明，反式至顺式异构化导致体积变化可忽略不计（0.9 +/- 0.4 mL mol（-1））和焓变为18 +/- 3 kcal mol（-1）。与mepepy的反式至顺式跃迁相关的声波在频率上与量热参考的声波重叠的事实意味着，构象跃迁的发生速度快于类似于声检测器的50 ns响应时间。实验结果与理论研究的比较提供了一种机理的证据，在该机理中，pepepy的反式至顺式异构化导致水分子与mepepy的吡啶环之间的氢键丢失。

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