Ultrafast capture of electrons ejected by photoionization leading to the formation of a charge-separated state at a high energy level
Ultrafast capture of electrons ejected by photoionization leading to the formation of a charge-separated state at a high energy level
复制标题
DOI：
10.1039/d0cp02029j
复制
发表时间：
2020-08-21
影响因子：
3.3
通讯作者：
Miyasaka, Hiroshi
中科院分区：
文献类型：
--
作者：
Kawakami, Tomomi;Koga, Masafumi;Miyasaka, Hiroshi
利用瞬态吸收光谱研究了高激发态双光子电离驱动的电子转移反应，旨在发展一种产生电荷分离态（CS）的方法，该态具有大的形成速率、高的能级和长的寿命.在使用芘和联苯作为模型系统的原理验证实验中，飞秒瞬态吸收光谱显示，在355 nm处的紫外激光脉冲的强烈照射下，通过分步双光子吸收有效地将芘泵浦到更高的激发态，然后发生电离过程。从芘中射出的电子被联苯直接捕获，时间常数为200 fs，而没有电子在溶液中的扩散过程。由此形成的CS态（Py+-Bp（-））的能级估计比芘的S-1态的能级高0.53eV。此外，在亚纳秒到纳秒的时间范围内，随后的离子解离没有显著的成对复合，有效地避免了CS态的数量损失。通过应用双光子激发方法，我们在实验上实现了超越传统电子转移反应框架的高能量长寿命CS态的超快形成。
Electron transfer reactions driven by two-photon ionization in the higher excited state were investigated via transient absorption spectroscopy, with the aim to develop a method for creating the charge-separated (CS) state with a large formation rate, high energy level, and long lifetime. In the proof-in-principle experiments using pyrene and biphenyl as a model system, femtosecond transient absorption spectroscopy revealed that intense irradiation of an ultraviolet laser pulse at 355 nm efficiently pumps up pyrene into a higher excited state via a stepwise two-photon absorption, and then an ionization process takes place. An electron ejected from pyrene is directly captured by biphenyl with a time constant of 200 fs without the diffusion process of the electron in solution. The energy level of the CS state (Py+-Bp(-)) thus formed was estimated to be higher than that of the S-1 state of pyrene by 0.53 eV. In addition, the subsequent ionic dissociation without a remarkable geminate recombination in the sub-nanosecond to nanosecond time region effectively avoids the quantity loss of the CS state. By applying the two-photon excitation method, we experimentally achieved ultrafast formation of the long-lived CS state at a high energy beyond the traditional framework of electron transfer reactions.