Harvey Jacob A, Thompson Ward H
Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA.
J Chem Phys. 2015 Jul 28;143(4):044701. doi: 10.1063/1.4926936.
Nanostructured materials that can confine liquids have attracted increasing attention for their diverse properties and potential applications. Yet, significant gaps remain in our fundamental understanding of such nanoconfined liquids. Using replica exchange molecular dynamics simulations of a nanoscale, hydroxyl-terminated silica pore system, we determine how the locations explored by a coumarin 153 (C153) solute in ethanol depend on its charge distribution, which can be changed through a charge transfer electronic excitation. The solute position change is driven by the internal energy, which favors C153 at the pore surface compared to the pore interior, but less so for the more polar, excited-state molecule. This is attributed to more favorable non-specific solvation of the large dipole moment excited-state C153 by ethanol at the expense of hydrogen-bonding with the pore. It is shown that a change in molecule location resulting from shifts in the charge distribution is a general result, though how the solute position changes will depend upon the specific system. This has important implications for interpreting measurements and designing applications of mesoporous materials.
能够限制液体的纳米结构材料因其多样的性质和潜在应用而受到越来越多的关注。然而，我们对这种纳米受限液体的基本理解仍存在重大差距。通过对纳米级羟基封端的二氧化硅孔隙系统进行复制交换分子动力学模拟，我们确定了香豆素153（C153）溶质在乙醇中的探索位置如何取决于其电荷分布，而电荷分布可通过电荷转移电子激发来改变。溶质位置的变化由内能驱动，与孔隙内部相比，内能使C153更倾向于处于孔隙表面，但对于极性更强的激发态分子则不然。这归因于乙醇对大偶极矩激发态C153更有利的非特异性溶剂化作用，代价是与孔隙形成氢键。结果表明，电荷分布变化导致的分子位置变化是一个普遍结果，尽管溶质位置如何变化将取决于具体系统。这对于解释介孔材料的测量结果和设计其应用具有重要意义。
