Real-Time Observation of Tight Au-Au Bond Formation and Relevant Coherent Motion upon Photoexcitation of [Au(CN)2-] Oligomers
Real-Time Observation of Tight Au-Au Bond Formation and Relevant Coherent Motion upon Photoexcitation of [Au(CN)2-] Oligomers
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DOI：
10.1021/ja310004z
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发表时间：
2013-01-16
影响因子：
15
通讯作者：
Tahara, Tahei
中科院分区：
文献类型：
--
作者：
Iwamura, Munetaka;Nozaki, Koichi;Tahara, Tahei
用皮秒/飞秒时间分辨发射光谱和吸收光谱研究了激发态低聚物[Au(CN)(2)(-)](N)形成紧密Au-Au键的结构动力学。在水溶液中选择性激发三聚体[Au(CN)(2)(-)](3)，在600 nm附近观察到激发态三聚体的瞬时吸收。这一瞬变显示出显著的强度增加(tau=2.1ps)，并在早期皮秒时间区域发生蓝移。密度泛函理论(DFT)和含时密度泛函理论计算表明，所观察到的光谱变化可以归因于三重态激发态三聚体从弯曲结构到线性交错结构的结构变化。瞬时吸收也表现出明显的峰位调制，反映了光激发引起的相干核波包运动。相干运动的频率分别为66和87 cm(-1)，与密度泛函理论计算的三棱镜激发态两个Au-Au伸缩振动的频率非常一致。亚纳秒区的时间分辨发射光谱表明，激发态三聚体与基态单体的缔合速度为tau=2.0 ns，生成激发态四聚体。
Structural dynamics involving tight Au-Au bond formation of excited-state oligomers [Au(CN)(2)(-)](n) was studied using picosecond/femtosecond time-resolved emission and absorption spectroscopy. With selective excitation of the trimer ([Au(CN)(2)(-)](3)) in aqueous solutions, transient absorption due to the excited-state trimer was observed around 600 nm. This transient exhibited a significant intensity increase (tau = 2.1 ps) with a blue shift in the early picosecond time region. Density functional theory (DFT) and time-dependent DFT calculations revealed that the observed spectral changes can be ascribed to a structural change from a bent to a linear staggered structure in the triplet excited-state trimer. The transient absorption also exhibited a clear modulation of the peak position, reflecting coherent nuclear wave packet motion induced by photoexcitation. The frequencies of the coherent motions are 66 and 87 cm(-1), in very good accord with the frequencies of two Au-Au stretch vibrations in the excited state of the trirner calculated by DFT. Time-resolved emission spectra in the subnanosecond time region showed that association of the excited-state trimer with the ground-state monomer proceeds with tau = 2.0 ns, yielding the excited-state tetramer.