Starovoytov Oleg N, Zhang Pengzhi, Cieplak Piotr, Cheung Margaret S
Department of Physics, University of Houston, Houston, Texas 77204, USA.
Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037, USA.
Phys Chem Chem Phys. 2017 Aug 30;19(34):22969-22980. doi: 10.1039/c7cp03177g.
The light-harvesting molecular triad consisting of carotenoid polyene (C), diaryl-porphyrin (P) and pyrrole-fullerene (C) is a donor-acceptor molecule capable of absorbing incident light in the visible range. Its ability to convert solar energy to electrical excitation and charge separation energy suggests a great potential in real-world applications. The ensemble of its conformations under ambient conditions varies widely according to its electronic state. In previous work, we applied a non-polarizable model to study the conformational distribution of the molecular triad in the ground and charge separated states. However, due to the lack of polarization, which imparts subtle changes in the charge distribution on atoms, molecular simulations fail to produce accurate average dipole moments. We developed the first polarizable model for a molecular triad to investigate the structural and dynamic properties of a molecular triad in the ground state in an explicit organic solvent, tetrahydrofuran (THF). We performed first-principles electronic structure calculations of the individual components in the triad as well as THF and then fit the partial atomic charges to the electrostatic potential using the i-RESP methodology. We validated these force field parameters by comparing the thermodynamic and dynamic properties obtained from molecular dynamics simulations with those from experiments. We enhanced the sampling of the triad conformations with replica exchange molecular dynamics simulations. We characterized the effects of induced polarization on the structural stability of the triad by analyzing the free energy landscapes constructed with polarizable force fields. Furthermore, by using principal component analysis, we found that the molecular triad conformations adopted a small range of torsional angles with induced polarization. The triad conformation solvated in polar solvent with a polarizable force field qualitatively agrees with that obtained from nuclear magnetic resonance spectroscopy.
由类胡萝卜素多烯（C）、二芳基卟啉（P）和吡咯 - 富勒烯（C）组成的光捕获分子三联体是一种能够吸收可见光范围内入射光的供体 - 受体分子。它将太阳能转化为电激发和电荷分离能的能力表明其在实际应用中具有巨大潜力。在环境条件下，其构象集合根据其电子状态有很大差异。在之前的工作中，我们应用了一个非极化模型来研究分子三联体在基态和电荷分离态下的构象分布。然而，由于缺乏极化，极化会使原子上的电荷分布产生细微变化，分子模拟无法产生准确的平均偶极矩。我们开发了第一个用于分子三联体的极化模型，以研究在明确的有机溶剂四氢呋喃（THF）中处于基态的分子三联体的结构和动力学性质。我们对三联体中的各个组分以及THF进行了第一性原理电子结构计算，然后使用i - RESP方法将部分原子电荷拟合到静电势上。我们通过将分子动力学模拟获得的热力学和动力学性质与实验结果进行比较，验证了这些力场参数。我们用副本交换分子动力学模拟增强了三联体构象的采样。我们通过分析用极化力场构建的自由能景观，表征了诱导极化对三联体结构稳定性的影响。此外，通过主成分分析，我们发现分子三联体构象在诱导极化下采用了小范围的扭转角。在具有极化力场的极性溶剂中溶剂化的三联体构象在定性上与从核磁共振光谱获得的结果一致。
