Citation: Hanchun Chen, Mingyi Liu, Haodong Ji. Principle of excited state defluorination for perfluorocarboxylic acids in photolysis reaction[J]. Chinese Chemical Letters, ;2026, 37(7): 112273. doi: 10.1016/j.cclet.2025.112273 shu

Principle of excited state defluorination for perfluorocarboxylic acids in photolysis reaction

Eco-environment and Resource Efficiency Research Laboratory, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China

jihaodong@pku.edu.cn

Received Date: 22 May 2025
Revised Date: 17 November 2025
Accepted Date: 11 December 2025
Available Online: 12 December 2025

Figures(3)

The degradation of perfluorocarboxylic acids (PFCAs), persistent organic pollutants, remains a significant environmental challenge. Photolysis represents a key pathway for their degradation, yet the molecular mechanisms driving defluorination and decarboxylation remain unclear. This study investigates the first step of direct PFCA photolysis by analyzing excitation properties using density functional theory (DFT), aiming to elucidate the relationship between electronic structure changes and degradation pathways. To better demonstrate and analyze the impact of internal factors on the first step of PFCAs photolysis, quantum chemical calculations were conducted to quantify and compare the molecule’s properties in the ground state and the excited state, aiming to explore the changes in the molecule’s behavior. Key parameters, including α C–F bond elongation (0.31%–1.62%), α C–C bond contraction (−6.23% to −9.10%), and excitation energy reduction (5.76–5.47 eV), revealed chain-length-dependent trends. The lower bond dissociation energy of α C–C (90–93 kcal/mol) compared to α C–F (116–124 kcal/mol) rationalized the dominance of decarboxylation over defluorination. Charge transfer spectroscopy further indicated localized n → π* excitation at carboxyl groups, promoting decarboxylation. A quantitative structure-activity relationship (QSAR) model linking hole-electron indices to degradation rates (R² = 0.91) was developed and validated via leave-one-out cross-validation (RMSE = 0.338). These findings not only advance the mechanistic understanding of PFCA photolysis but also provide a predictive tool for optimizing UV-based water treatment systems targeting persistent fluorinated pollutants.
- Perfluorocarboxylic acids,
- Excitation,
- DFT calculations,
- Photolysis,
- Persistent organic pollutants
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