标题： 溶液中电子激发的PtPOP复合物的退相干和振动能量弛豫 显示英文标题

标题： Decoherence and vibrational energy relaxation of the electronically excited PtPOP complex in solution

摘要： 理解分子在凝聚相中光激发后的超快振动弛豫对于预测光诱导分子过程的结果并提高其效率至关重要。 在此，通过直接绝热动力学模拟研究了在液态水和乙腈中电子激发后双核配合物 [Pt$_2$(P$_2$O$_5$H$_2$)$_4$]$^{4-}$ (PtPOP) 的振动退相干和能量弛豫。 使用了一种量子力学/分子力学 (QM/MM) 方法，其中配合物的激发态通过轨道优化密度泛函计算进行建模，而溶剂分子则使用势能函数进行描述。 发现主导光诱导动力学的 Pt-Pt 振动的退相干时间为$\sim$1.6 ps，在两种溶剂中均如此。 这与水中实验测量结果非常一致，其中系间窜越较慢（$>10$ps）。 通过监测溶剂在振动模式上的功率来确定过量能量的流动路径。 后者是从速度协方差中获得的广义正则模式，并使用QM/MM嵌入力计算功率。 发现过量振动能主要通过配体原子与周围溶剂分子之间的短程排斥和吸引相互作用释放，而涉及Pt原子的溶质-溶剂相互作用则不太重要。 由于光激发将大部分过量能量注入Pt-Pt振动中，因此能量耗散到溶剂中效率较低。 这项研究揭示了光激发PtPOP复合物在溶液中异常长的振动相干性的机制，并强调了短程相互作用对于准确模拟溶剂化分子的振动能量弛豫的重要性。 显示英文摘要

摘要： Understanding the ultrafast vibrational relaxation following photoexcitation of molecules in a condensed phase is essential to predict the outcome and improve the efficiency of photoinduced molecular processes. Here, the vibrational decoherence and energy relaxation of a binuclear complex, [Pt$_2$(P$_2$O$_5$H$_2$)$_4$]$^{4-}$ (PtPOP), upon electronic excitation in liquid water and acetonitrile are investigated through direct adiabatic dynamics simulations. A quantum mechanics/molecular mechanics (QM/MM) scheme is used where the excited state of the complex is modelled with orbital-optimized density functional calculations while solvent molecules are described using potential energy functions. The decoherence time of the Pt-Pt vibration dominating the photoinduced dynamics is found to be $\sim$1.6 ps in both solvents. This is in excellent agreement with experimental measurements in water, where intersystem crossing is slow ($>10$ ps). Pathways for the flow of excess energy are identified by monitoring the power of the solvent on vibrational modes. The latter are obtained as generalized normal modes from the velocity covariances, and the power is computed using QM/MM embedding forces. Excess vibrational energy is found to be predominantly released through short-range repulsive and attractive interactions between the ligand atoms and surrounding solvent molecules, whereas solute-solvent interactions involving the Pt atoms are less important. Since photoexcitation deposits most of the excess energy into Pt-Pt vibrations, energy dissipation to the solvent is inefficient. This study reveals the mechanism behind the exceptionally long vibrational coherence of the photoexcited PtPOP complex in solution and underscores the importance of short-range interactions for accurate simulations of vibrational energy relaxation of solvated molecules.