Institute of Computational Biological Chemistry, University of Vienna, Vienna, Austria.
J Phys Chem A. 2009 Dec 24;113(51):14039-51. doi: 10.1021/jp903546h.
This work deals with a molecular dynamics simulation analysis of the intramolecular vibrational energy transfer in a system of two chromophores, azulene and anthracene, bridged by an aliphatic chain and is motivated by corresponding laser experiments. After selective excitation of the azulene chromophore, the subsequent intramolecular vibrational energy redistribution is monitored by analyzing the transient temperatures of the two chromophores and the chain between them. The main focus concerns the heat conduction process in the chain. Therefore, the chain length was varied from 0 to 19 CH(2) units. In addition, methoxymethyl, 1,2-dimethoxyethyl, and a thiomethoxymethyl chains were studied. The investigation of the intramolecular vibrational energy process was decomposed into a temporal analysis and a spatial analysis. For short alkyl chains, the time constant of energy relaxation increases proportionally to the chain length. However, for longer chains, the time constant characterizing the energy decay of the azulene chromophore saturates and becomes independent of the chain length. This behavior is consistent with experimental findings. The spatial analysis shows more or less exponential decay of the temperature along the chain near the excited chromophore. In additional simulations, the two chromophores were thermostatted at different temperatures to establish a constant heat flux from the azulene to the anthracene side. The steady-state temperature profiles for longer alkyl chains show strong gradients near the two chromophores and constant but weak gradients in the central part of the chain. Both simulation methods indicate that strong Kapitza effects at the boundaries between each chromophore and the molecular chain dominate the intramolecular energy flux.
这项工作涉及通过分子动力学模拟分析两个发色团（蓝烯和蒽）之间通过脂肪链桥接的分子内振动能量转移，这是受相应激光实验的启发。在选择性激发蓝烯发色团后，通过分析两个发色团和它们之间的链的瞬态温度来监测随后的分子内振动能量再分配。主要关注点是链中的热传导过程。因此，改变了链长从 0 到 19 CH(2) 个单位。此外，还研究了甲氧基甲基、1,2-二甲氧基乙基和硫甲氧基甲基链。对分子内振动能量过程的研究分解为时间分析和空间分析。对于短链烷基，能量弛豫的时间常数与链长成正比增加。然而，对于较长的链，表征蓝烯发色团能量衰减的时间常数饱和并且与链长无关。这种行为与实验结果一致。空间分析表明，在靠近激发发色团的链上，温度或多或少呈指数衰减。在附加模拟中，将两个发色团在不同温度下进行恒温控制，以建立从蓝烯到蒽的恒定热通量。对于较长的烷基链，稳态温度分布在两个发色团附近表现出强烈的梯度，而在链的中心部分则表现出恒定但较弱的梯度。这两种模拟方法都表明，每个发色团和分子链之间边界处的强 Kapitza 效应主导了分子内能量通量。
