Recent experiments have shown that photoexcited pyridine can abstract a hydrogen atom from a water molecule in pyridine-water clusters containing at least four water molecules. To explain these findings, we explored the electron-driven proton-transfer reaction from water to pyridine in pyridine-(H₂O)_n, n = 1 – 4, complexes with ab initio methods. It is shown that the photoinduced electron/proton transfer reaction is energetically possible for all clusters. The calculations reveal that the hydrogen bond between pyridine and the adjacent water molecule is weakened (strengthened) in the ¹nπ∗ (¹ππ∗) excited state, which is unfavorable (favorable) for the H-atom transfer reaction. For pyridine-(H₂O)_n clusters with n = 1 - 3, the steepest descent path leads to a local minimum of nπ∗ character, while for the pyridine-(H₂O)₄ cluster, this path leads to a local minimum of ¹ππ∗ character. These results provide a tentative explanation of the experimental observations.

最近的实验表明，光激发的吡啶可以从含有至少四个水分子的吡啶-水簇中的一个水分子中提取一个氢原子。为了解释这些发现，我们用从头算方法研究了吡啶-（H ₂ O）_n（n = 1-4 ）中从水到吡啶的电子驱动质子转移反应。结果表明，对于所有团簇，光诱导的电子/质子转移反应在能量上都是可能的。计算表明，吡啶和相邻水分子之间的氢键在减弱（加强）^1个Nπ*（¹ ππ*）激发态，这是不利的（有利）的H-原子转移反应。对于吡啶-（H ₂ O）_nn = 1的簇- 3，最速下降路径通向局部最小值Nπ的*字符，而对于吡啶（H ₂ O）₄簇，此路径通向局部最小值的^1个ππ*字符。这些结果为实验观察提供了初步的解释。