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光致异构化是分子光物理与光化学反应的核心，其量子产率与激发态动力学演化路径相关。改变分子激发态演化路径以实现对光化学反应的精准操控是物理学家、化学家长期以来追求的梦想。本论文采用飞秒泵浦-受激亏蚀-探测（Pump-Dump-Probe）光谱技术，研究了Dump光脉冲对1,1’-二乙基-2,2’-碘化菁（1,1'-diethyl-2,2'-cyanine iodide，1122C）分子光异构化动力学的影响。在Pump-Probe实验中，1122C分子被Pump光激发之后，处于激发态的分子以5.6 ps的时间常数沿扭转反应坐标发生结构变化，从反式（Trans）构型转变为顺式（Cis）构型。为了对该反应进行人为调控，我们在传统Pump-Probe光谱的基础上，引入了第三束波长为1030 nm的飞秒Dump光。Dump光脉冲成功使部分处于激发态的Trans构型分子通过受激跃迁直接返回基态，绕过了原本通向Cis产物的异构化通道。通过比较Cis产物吸收信号的变化，计算得出Dump光作用下Cis构型的产率降低了约12.1%。我们的研究实现了利用飞秒激光对超快光化学反应路径的主动干预，展示了飞秒多脉冲光谱技术在调控分子激发态演化路径、优化光异构化反应产率的潜力。该研究为将来对复杂光化学反应精准操控提供了理论和技术支持。
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关键词:
- 飞秒瞬态吸收光谱 /
- 光异构化 /
- 激发态动力学 /
- 泵浦-受激亏蚀-探测
Photoisomerization is a prototypical photophysical and photochemical reaction, the reaction quantum yield depends on its excited-state dynamic. Altering the evolution path of molecular excited states to achieve precise control over photochemical reactions has long been a dream pursued by physicists and chemists. To investigate the effect of femtosecond laser pulse on the ultrafast reaction, the ultrafast photoisomerization of 1,1'-diethyl-2,2'-cyanine iodide (1122C) in methanol was studied using Pump-Dump-Probe spectroscopy. A third femtosecond pulse (Dump) at 1030 nm was introduced into the traditional pump-probe experiment, delayed by 1 ps relative to the initial pump pulse. The recovery of ground state bleaching (GSB) as well as decrease of the Cis product were observed in the Pump-Dump-Probe experiment. It suggests that the Dump pulse successfully promote the initial Trans form to skip the Trans-Cis isomerization pathway in the excited state and return to the ground state directly through stimulated emission. We found that the Cis yield was reduced approximately 12.1% under irradiation of the Dump pulse. Our research has successfully manipulated the quantum yields of a typic ultrafast photoisomerization reaction using femtosecond laser pulse, demonstrating the potential of femtosecond multi-pulse spectroscopy in modifying excited-state evolution pathways and optimizing photochemical reaction yields. This study provides theoretical and technical support for precise control of complex photochemical reactions in the future.-
Keywords:
- femtosecond transient absorption spectroscopy /
- photoisomerization /
- excited state dynamics /
- Pump-Dump-Probe
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