Corrections to “Vibrational Cooling in Oligomeric Viologens of Different Sizes and Topologies”
Corrections to “Vibrational Cooling in Oligomeric Viologens of Different Sizes and Topologies”
复制标题
对“不同尺寸和拓扑结构的低聚紫罗碱的振动冷却”的修正
DOI：
10.1021/acs.jpcb.9b07197
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Piotrowiak, Piotr
中科院分区：
文献类型：
--
作者：
Liu, Mengdi;Kawauchi, Takehiro;Iyoda, Tomokazu;Piotrowiak, Piotr
研究了一组含有甲基紫精重复单元（MV 2+）的同源二聚体和三聚体的振动冷却。单还原紫精（MV+·）的D1激发态通过锥形交叉点的<500 fs的快速衰减允许制备具有1.7 eV的大的过剩能量的振动热D 0基态，其相当于1.800 K的初始有效温度。泵浦-探测光谱用于监测特征D 0 → D1热吸收带的消失，该吸收带出现在比与溶剂平衡的“冷”MV+·的稳态光谱更长的波长处。据推测，地面的振动激发最初被限制在相同的单还原紫精重复单元，这是光学激发到本地化的电子D1状态，虽然一定程度的再分配可能已经发生在激发态。所观察到的冷却速率取决于低聚物的尺寸和拓扑结构，线性三聚体表现出显着更快的热化比支链的。在谐波近似下进行的分子动力学模拟证实了实验结果。在这些系统中的热平衡的动力学似乎是一致的，主要是弹道初始传播的振动过剩能量的距离大至1.4nm，并建议在分支三聚体的等效途径之间的干扰的存在。
Vibrational cooling was investigated in a set of homologous dimers and trimers with methyl viologen repeat units (MV2+). The rapid, <500 fs decay of the D1excited state of monoreduced viologen (MV+•) via a conical intersection allows the preparation of a vibrationally hot D0ground state with a large excess energy of 1.7 eV, which is equivalent to the initial effective temperature of ∼800 K. Pump-probe spectroscopy was used to monitor the disappearance of the characteristic D0→ D1hot absorption band, which appears at longer wavelengths than the steady-state spectrum of “cold” MV+•in equilibrium with the solvent. It is assumed that the vibrational excitation of the ground is initially confined to the same monoreduced viologen repeat unit, which was optically excited to the localized electronic D1state, although some degree of redistribution may occur already in the excited state. The observed cooling rates depend on the size and topology of the oligomer, with the linear trimer exhibiting significantly faster thermalization than the branched one. The experimental results were corroborated by molecular dynamics simulations carried out in the harmonic approximation. The dynamics of the thermal equilibration in these systems appears to be consistent with primarily ballistic initial propagation of the vibrational excess energy over distances as large as ∼4 nm and suggests the presence of interference between the equivalent pathways in the branched trimer.