Ultrafast photofragment ion spectroscopy of the Wolff rearrangement in 5-diazo Meldrum's acid.
Ultrafast photofragment ion spectroscopy of the Wolff rearrangement in 5-diazo Meldrum's acid.
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DOI：
10.1039/c3cp55365e
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发表时间：
2014-03
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影响因子：
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通讯作者：
Andreas F. Steinbacher;Sebastian Roeding;T. Brixner;P. Nuernberger
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文献类型：
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作者：
Andreas F. Steinbacher;Sebastian Roeding;T. Brixner;P. Nuernberger
我们利用飞秒光碎片离子光谱研究了光刻中使用的光活性化合物5-重氮梅尔德鲁姆酸（DMA）的气相光化学。溶液中的瞬态吸收研究揭示了紫外激发后分子内超快的Wolff重排为烯酮，随后的反应也涉及溶剂。由于在气相研究中没有溶剂分子，我们能够纯粹地关注Wolff重排的光化学和随后的反应步骤。对时间分辨光碎片离子信号的观察使我们能够区分烯酮和烃产物的动力学。通过对某片段离子信号的不同可能分子来源的鉴定，推断出了沃尔夫重排的时间尺度和烯酮产物的寿命。我们进一步确定了来自二氧化碳产物的第二个沃尔夫重排的实验特征，正如从热解研究中间接推测的那样。
We investigate the gas-phase photochemistry of 5-diazo Meldrum's acid (DMA), a photoactive compound used in lithography, by femtosecond photofragment ion spectroscopy. Transient-absorption studies in solution had revealed an ultrafast intramolecular Wolff rearrangement to a ketene after UV excitation, followed by reactions which also involve the solvent. Due to the absence of solvent molecules in this gas-phase study, we are able to focus purely on the photochemistry of the Wolff rearrangement and subsequent reaction steps. The observation of the time-resolved photofragment ion signals allows us to discriminate the dynamics of ketene and carbene products. By identification of the different possible molecular origins for a certain fragment ion signal, the time scale of the Wolff rearrangement and the lifetime of the ketene product are inferred. We further identified experimental signatures of a second Wolff rearrangement emanating from the carbene product, as had been conjectured indirectly for this molecule from pyrolysis studies.