We investigated the charge-transfer dynamics between distinctive excited states of a carotenoid–porphyrin–C₆₀ molecular triad in tetrahydrofuran solvent. Our approach combines all-atom molecular dynamics simulations with an explicit solvent and electronic-state-specific force fields with a recently proposed hierarchy of approximations based on the linearized semiclassical method. The validity of the second-order cumulant approximation, which leads to a Marcus-like expression for the rate constants, was established by comparing the rate constants calculated with and without resorting to this approximation. We calculated the rate constants between the porphyrin-localized ππ* state, porphyrin-to-C₆₀ charge-transfer state, and carotenoid-to-C₆₀ charge-separated state for the bent and linearly extended conformations. In agreement with our earlier finding, the charge separation was found to occur via a two-step mechanism, where the second step is switched on by the bent-to-linear conformational change. By comparing the rate constants calculated for a flexible and a rigid triad molecule, while allowing the solvent molecules to fluctuate, we showed that the charge-transfer process is driven by the solvent, rather than by the triad’s intramolecular degrees of freedom. We further calculated the triad’s amide I stretch frequency distributions and found them to be highly sensitive to the electronic state, thereby demonstrating the possibility of monitoring charge-transfer dynamics in this system via UV–vis/IR pump–probe spectroscopy.

中文翻译：

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显式四氢呋喃中溶解的类胡萝卜素-卟啉-C ₆₀分子三元组中电荷转移动力学的计算研究及其光谱学特征

我们研究了四氢呋喃溶剂中类胡萝卜素–卟啉– C ₆₀分子三元组的独特激发态之间的电荷转移动力学。我们的方法将全原子分子动力学模拟与显式溶剂和特定于电子态的力场相结合，并基于线性化半经典方法基于最近提出的近似层次。通过比较使用和不使用此近似值时计算出的速率常数，可以确定二阶累积量逼近的有效性，从而得出速率常数类似Marcus的表达式。我们计算了卟啉局部化的ππ*状态，卟啉对C _60的电荷转移状态和类胡萝卜素对C ₆₀的速率常数弯曲和线性延伸构象的电荷分离状态。与我们先前的发现一致，发现电荷分离是通过两步机制进行的，其中第二步通过弯曲到线性构象变化开启。通过比较为柔性和刚性三单元组分子计算的速率常数，同时允许溶剂分子波动，我们表明电荷转移过程是由溶剂驱动的，而不是由三单元组的分子内自由度驱动的。我们进一步计算了三单元组的酰胺I拉伸频率分布，发现它们对电子状态高度敏感，从而证明了通过UV-vis / IR泵浦-探针光谱监测该系统中电荷转移动力学的可能性。