Pang Xiaojuan, Jiang Chenwei, Xie Weiwei, Domcke Wolfgang
Key Laboratory for Quantum Information and Quantum Optoelectronic Devices, Shaanxi, China and Department of Applied Physics, Xi'an Jiaotong University, Xi'an 710049, China and Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany.
Key Laboratory for Quantum Information and Quantum Optoelectronic Devices, Shaanxi, China and Department of Applied Physics, Xi'an Jiaotong University, Xi'an 710049, China.
Phys Chem Chem Phys. 2019 Jul 14;21(26):14073-14079. doi: 10.1039/c8cp07015f. Epub 2019 Jan 24.
It has been found in recent molecular beam experiments that pyridine molecules photoexcited at 255 nm can abstract hydrogen atoms from hydrogen-bonded water molecules in pyridine-water clusters, resulting in pyridinyl-hydroxyl radical pairs. The reaction could only be detected for clusters containing at least four water molecules. To provide insight into the mechanisms of this reaction, we performed ab initio excited-state trajectory surface-hopping dynamics simulations for two pyridine-water complexes, containing one and four water molecules, respectively, using the second-order algebraic-diagrammatic-construction (ADC(2)) electronic-structure method. A computationally efficient surface-hopping algorithm based on the Landau-Zener formula has been used to evaluate the transition probability between electronic states. The formation of the pyridinyl radical via an electron-driven proton transfer (EDPT) process from water to pyridine is confirmed by the simulations. The analysis of the competing excited-state reaction mechanisms up to 500 fs reveals that adiabatic relaxation to local minima of the S(nπ*) potential-energy surface is the dominant channel in both clusters, followed by internal conversion to the electronic ground state via so-called ring-puckering conical intersections. The efficiency of the latter contribution is weakly dependent of the size of the clusters. The EDPT reaction occurs on the fastest time scales (faster than 200 fs) with a branching ratio of several percent. It is found to be four times more efficient in the pyridine-(HO) cluster than in the pyridine-HO cluster, which is qualitatively consistent with the experimental observations. A detailed understanding of the photoinduced reaction mechanisms in complexes of N-heterocyclic chromophores with water molecules is of relevance for future systematic knowledge-based developments of optimized materials for photocatalytic water splitting with sunlight.
最近的分子束实验发现，在255nm处光激发的吡啶分子可以从吡啶 - 水簇中氢键结合的水分子中提取氢原子，从而产生吡啶基 - 羟基自由基对。该反应仅在含有至少四个水分子的簇中才能检测到。为了深入了解该反应的机制，我们分别使用二阶代数图示构造（ADC(2)）电子结构方法，对分别含有一个和四个水分子的两种吡啶 - 水络合物进行了从头算激发态轨迹表面跳跃动力学模拟。基于朗道 - 齐纳公式的一种计算效率高的表面跳跃算法已被用于评估电子态之间的跃迁概率。模拟证实了通过从水到吡啶的电子驱动质子转移（EDPT）过程形成吡啶基自由基。对高达500fs的竞争激发态反应机制的分析表明，绝热弛豫到S(nπ*)势能面的局部最小值是两个簇中的主要通道，随后通过所谓的环皱缩锥形交叉点内转换到电子基态。后一种贡献的效率与簇的大小弱相关。EDPT反应在最快的时间尺度上发生（快于200fs），分支比为百分之几。发现在吡啶-(HO)簇中比在吡啶 - HO簇中效率高四倍，这在定性上与实验观察结果一致。详细了解N - 杂环发色团与水分子络合物中的光诱导反应机制，对于未来基于系统知识开发用于太阳光光催化水分解的优化材料具有重要意义。
