Fluorinated compounds play indispensable roles across pharmaceutical, agrochemical, and materials science due to fluorine’s unique electronegativity, small atomic radius, and high metabolic stability. Among them, trifluorothioanisole (Ph–S–CF3) serves as a representative functionally model system for environmental photochemistry, given the widespread use of the –SCF3 group in agrochemicals and its concerning persistence. However, the ultrafast photodynamics and non-radiative decay mechanisms of Ph–S–CF3 remain poorly understood, limiting predictive insight into its environmental fate. Here, we combine high-level static electronic structure calculations with excited-state non-adiabatic dynamics simulations to unravel the mechanism of Ph–S–CF3. Our results reveal that excitation to the S1 state initiates ultrafast internal conversion via two competitive bond-cleavage pathways mediated by distinct conical intersections: dissociation at either the S1–C3 or S1–CF3 bond, yielding ·CF3 (46%) and ·SCF3 (54%) radicals, with an overall S1 lifetime of ∼612 fs. These findings not only elucidate the photodegradation mechanism of a prominent fluorinated environmental contaminant but also provide a general theoretical framework for predicting the photostability and formation dynamics of persistent radical species (·CF3/·SCF3) derived from –SCF3-functionalized compounds, underscoring the regulatory role of fluorine substitution in excited-state dynamics. Thereby, this study provides a crucial basis for assessing the environmental persistence and ecotoxicity of fluorinated organics and offers strategic guidance for the rational design of low-persistence fluorinated functional molecules.
Zhao et al. (Fri,) studied this question.
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