The Center for Modeling and Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan 250100, People's Republic of China.
J Chem Phys. 2013 Jan 7;138(1):014310. doi: 10.1063/1.4773398.
We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H(2)O)(n)). Calculated results illustrate that Bz ring and water clusters are indeed linked through the π···HO interactions in the neutral Bz(H(2)O)(n) (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the π system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (π*) of the Bz ring, and the π···HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak π···HO interaction plays an important role as the driving force in conversion of the two states.
我们提出了一个结合 M06 功能计算和从头分子动力学模拟的研究，研究了一个多余电子（EE）在微水合芳香族复合物（由苯（Bz）-水二元团簇模拟，Bz（H（2）O）（n））中的状态和动力学。计算结果表明，在中性 Bz（H（2）O）（n）（n = 1-8）团簇中，Bz 环和水分子团确实通过 π···HO 相互作用连接，并且水分子团的大小不影响其与 π 系统的相互作用对于寡水合复合物。也确定了被捕获在这种 Bz-水团簇中的 EE 的状态和动力学。EE 可能的局域化状态大致可以分为两种类型：（i）单个，环局域化状态（以 Bz 为中心的价阴离子），其中 EE 占据了复合物的 LUMO，该复合物起源于 Bz 环的 LUMO（π*），并且 π···HO 相互作用增强，Bz 环的电子密度增加。在这种模式下，由于 Bz 部分的电子密度增加和由相互作用的 H-O 键引起的电子密度非对称分布，Bz 的碳骨架发生明显变形;（ii）溶剂化状态，其中 EE 直接作为表面态被水分子的悬空氢原子或由 Bz 和水分子团形成的混合腔中的溶剂化态捕获。在后一种情况下，Bz 也可以使用其芳香环边缘的 C-H 键作为腔的一部分参与捕获 EE。一般来说，小的水分子团有利于 Bz 中心的价阴离子状态，而大的水分子团则有利于溶剂化电子状态。水分子的波动和重排可以充分改变 EE 状态的相对能量，从而允许 EE 从 Bz 中心状态到水分子团中心状态的容易转换。这表明芳香族 Bz 可以被识别为电子转移的踏脚石，而弱的 π···HO 相互作用作为两种状态转换的驱动力起着重要作用。
