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Ultrafast Investigation of Excited-State Dynamics in Trans-4-methoxyazobenzene Studied by Femtosecond Transient Absorption Spectroscopy
Ya-ping Wang,Chun-hua Li,Bing Zhang,Chen Qin*,Song Zhang*
Author NameAffiliationE-mail
Ya-ping Wang School of Electronic Science & Applied Physics, Hefei University of Technology, Hefei 230009, China  
Chun-hua Li School of Electronic Science & Applied Physics, Hefei University of Technology, Hefei 230009, China  
Bing Zhang State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China  
Chen Qin* Key Laboratory of Mineral Luminescent Material and Microstructure of Xinjiang, School of Physics and Electronic Engineering, Xinjiang Normal University, Urumqi 830054, China qinchen5555@sina.com 
Song Zhang* State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China zhangsong@wipm.ac.cn 
Abstract:
The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S2 state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400-480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S2 to S1 state. The other relaxation pathways are correlated with the decay of the S1 state via internal conversion and isomerization, and the vibrational cooling of the hot S0 state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.
Key words:  Photoisomerization, Trans-4-methoxyazobenzene, Femtosecond transient absorption spectroscopy
FundProject:
反式-4-甲氧基偶氮苯超快激发态性质研究
王雅萍,李春华,张 冰,秦 晨*,张 嵩*
摘要:
本文利用飞秒瞬态吸收光谱结合量化计算研究了反式-4-甲氧基偶氮苯的超快激发态动力学和光异构过程. 瞬态光谱中在400∽480 nm波段出现永久的正吸收,表明反式分子被激发到第二激发态后最终产生了顺式结构. 在乙醇和乙二醇溶剂环境中分别获得了三个衰减组分,时间分别为0.11、1.4、2.9 ps和0.16、1.5、7.5 ps. 快速的时间组分是源自第二激发态弛豫到第一激发态的内转换过程. 另外两个组分和第一激发态的弛豫相关:一个是经第一激发态的内转化和光异构过程,另一个是顺式结构的振动冷却过程. 基于不同溶剂环境中的动力学差别,证实了光异构路径是反转机制而不是旋转机制.
关键词:  光异构,反式-4-甲氧基偶氮苯,飞秒瞬态吸收光谱
DOI:10.1063/1674-0068/31/cjcp1806155
分类号: