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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Syntheses, structures, and photoisomerization of (E)- and (Z)-2-tert-butyl-9-(2,2,2-triphenylethylidene)fluorene
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Syntheses, structures, and photoisomerization of (E)- and (Z)-2-tert-butyl-9-(2,2,2-triphenylethylidene)fluorene

机译：（E）-和（Z）-2-叔丁基-9-（2,2,2-三苯乙叉基）芴的合成，结构和光异构化

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摘要

"Sterically geared" 9-(2,2,2-triphenylethylidene)fluorene (1) is of potential interest as a photoactive moiety in molecular devices, and the 2-tert-butyl derivative (6) has been synthesized to investigate photoisomerization. E and Z stereoisomers of 6 were separated and identified by X-ray crystallography. The tert-butyl group does not introduce additional strain, and its close proximity to the trityl group in the Z isomer suggests an attractive van der Waals interaction. The UV spectra of (E)-6 and (Z)-6 are nearly identical, showing absorption bands that are similar to those of fluorene occurring at wavelengths longer than 240 nm. Photoisomerization of 6 was investigated at 266, 280 and 320 rim. Solutions initially containing only (E)-6 or (Z)-6 were irradiated with pulsed laser light, monitoring isomerization by H-1 NMR spectroscopy. Negligible photodecomposition was observed when the solutions were agitated by N-2 ebullition. Experimental data were fitted to theoretical curves to obtain photoisomerization quantum yields (phi(ZE) and phi(EZ)) ranging from 0.04 to 0.09. This first photoisomerization study of a dibenzofulvene reveals significant quantum yields, despite theoretical prediction of inefficient or negligible isomerization of the parent hydrocarbon, fulvene. Thermal isomerization of 6 at 270 degrees C (t(1/2) = 120 min) was also followed by H-1 NMR spectroscopy, resulting in an estimated activation energy (Delta G*) of 43 kcal/mol.
机译：作为分子装置中的光敏部分，“立体齿轮” 9-（2,2,2-三苯乙叉基）芴（1）具有潜在的意义，并且已经合成了2-叔丁基衍生物（6）以研究光异构化。分离出6的E和Z立体异构体，并通过X射线晶体学鉴定。叔丁基不引入额外的应变，并且它与Z异构体中的三苯甲基非常接近，表明它们具有有吸引力的范德华相互作用。 （E）-6和（Z）-6的紫外光谱几乎相同，显示出与在波长大于240 nm的芴相似的吸收带。在266、280和320边缘研究了6的光异构化。用脉冲激光照射最初仅包含（E）-6或（Z）-6的溶液，并通过H-1 NMR光谱监测异构化。当通过N-2沸腾搅动溶液时，观察到可忽略的光分解。将实验数据拟合至理论曲线以获得光异构化量子产率（phi（ZE）和phi（EZ）），范围为0.04至0.09。尽管理论上预测母体富烯烯的低效或可忽略不计的异构化，但对二苯并富烯的首次光致异构化研究显示出显着的量子产率。还通过H-1 NMR光谱在270摄氏度下进行6的热异构化（t（1/2）= 120分钟），得出的活化能估计值（Delta G *）为43 kcal / mol。

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