Photodegradation of the insecticide pymetrozine (PYM) was studied on surface of wax films, and in aqueous and nonaqueous phase. The half-life of PYM on the wax surface was approximately 250 times longer than in water. Scavenging experiments, laser flash photolysis, and spectra analysis indicated the first singlet excited state of PYM (S1 *_PYM) to be the most important photoinduced species initiating the photodegradation. Quantum chemistry calculations identified significant molecular torsion and changes in the structure C–CN–N of S1 *_PYM, and the absolute charges of the CN atoms increased and the bond strength weakened. Free energy surface analysis, and O¹⁸ labeling experiments further confirmed that the mechanism was two-step photoinduced hydrolysis. The first step is the hydrolysis of S1 *_PYM at CN upon reaction with 2–3 water molecules (one H₂O molecule as the catalyst). The second step is an intramolecular hydrogen transfer coupled with the cleavage of C–N bond and formation of two cyclic products. During the interactions, water molecules experience catalytic activation by transferring protons, while there is a negligible solvent effect. Clarifying the detailed photodegradation mechanisms of PYM is beneficial for the development of green pesticides that are photostable and effective on leaf surfaces, and photolabile and detoxified in the aquatic environment.

在蜡膜表面、水相和非水相中研究了杀虫剂吡蚜酮 (PYM) 的光降解作用。PYM 在蜡表面的半衰期大约是在水中的 250 倍。清除实验、激光闪光光解和光谱分析表明 PYM 的第一个单重激发态 (S1 * _PYM ) 是引发光降解的最重要的光诱导物质。_{量子化学计算发现S1 * PYM}的分子发生明显的扭转和结构C-C N-N 的变化，C N 原子的绝对电荷增加，键强度减弱。自由能表面分析和 O ¹⁸标记实验进一步证实了该机制是两步光诱导水解。第一步是 S1 * _PYM在 C N 与 2-3 个水分子（一个 H ₂ O 分子作为催化剂）反应后水解。第二步是分子内氢转移，伴随着 C-N 键的断裂和两个环状产物的形成。在相互作用过程中，水分子通过转移质子经历催化活化，而溶剂效应可以忽略不计。阐明PYM详细的光降解机理，有利于开发对叶面光稳定有效，在水生环境中光不稳定和解毒的绿色农药。