Real-time probing of Energy Dissipation Processes in Solvated Clusters

本研究项目旨在通过超快时间分辨测量来微观理解溶剂化团簇中的能量耗散过程。由于实验装置的改进，如真空室和激光系统，取得了以下结果：研究了9,9′-双苯基（BA）与水的1:1簇，详细表征了BA中扭曲分子内电荷转移（TICT）反应。通过激光诱导荧光观察扭转过程，确定了BA在团簇中的扭转势。簇中的电势与单体中的电势大不相同，这表明BA的电子特性在络合作用下发生了相当大的改变，以及BA与水之间的空间排斥力。ps时间分辨荧光测量表明，TICT速率对激发能或溶剂同位素取代没有明显的依赖。更多的观察证实了TICT反应是通过“顺序”机制进行的；最初制备的能级主要耦合到具有扭转运动高振动激励的中间能级，这些中间能级进一步松弛到电荷分离状态的最终能级。这一结果证明了扭转运动在TICT反应动力学中的重要性。研究了9-吖啶酮（AD）的水溶剂化簇，探讨了微观溶剂化对AD中体系间交叉（ISC）的影响。随着溶剂化顺序的增加，荧光量子产率大大提高。特别是单体中仅加入一种水就能引起> ~ 200倍的剧烈变化，表明反应机理从直接ISC向二级ISC发生了交叉。通过JR-UV双共振光谱结合从头计算MO的结构表征表明，在1:1的簇中，水与AD的C=O形成了氢键。这些结果验证了选择性微溶剂化对ISC的影响。少

The present research project aims to microscopic understanding on the energy dissipation processes in solvated clusters through ultrafast time-resolved measurements. Owing to the improvement in the experimental setup, such as the vacuum chambers and laser systems, the following results have been achieved.1. The 1 : 1 cluster of 9,9'-bianthryl (BA) with water has been studied for detailed characterization of the twisted intramolecular charge transfer (TICT) reaction in BA.The torsional potential of BA in the cluster has been determined form the laser-induced-fluorescence observation of the torsional progressions. The potential in the cluster is much different from that in the monomer, indicating considerable modification in the electronic character of BA by complexation, as well as steric repulsion between BA and water. The ps time-resolved fluorescence measurements have shown that the TICT rate has no appreciable dependence on excitation energy or solvent isotopic substitution. This ob … More servation confirms that the TICT reaction proceeds via "sequential" mechanism ; the initially prepared level is predominately coupled to intermediate levels with high vibrational excitation of torsional motion, which further relax to the final levels in the charge-separated state. This result demonstrates the importance of the torsional motion in the dynamics of TICT reactions.2. The water-solvated clusters of 9-acridone (AD) have been studied to explore the microscopic solvation effect on inter-system crossing (ISC) in AD.The fluorescence quantum yield is greatly enhanced with increasing order of solvation. Especially, drastic change with>200-fold increase caused by addition of only one water to the monomer indicates the crossover of the reaction mechanism form the direct ISC to the second-order ISC.Structural characterization by JR-UV double resonance spectroscopy combined with ab initio MO calculation has shown that water is hydrogen-bonded to C=O of AD in the 1 : 1 cluster. These results validates the site-selective microsolvation effect on ISC. Less