Simulating UV Photolysis of Ibuprofen by Time-Dependent Excited-State Molecular Dynamics.

Organic micropollutants (OMPs) undergo direct photolysis in UV processes for water treatment. Quantum yields and photoproducts are important for understanding the photochemical behavior of OMPs and optimizing UV technologies. Here, we evaluated time-dependent excited-state molecular dynamics (TDESMD) as a computational approach for estimating wavelength-dependent quantum yields and photoproducts, using ibuprofen (IBU) as a model OMP. We performed TDESMD simulations at 254 and 222 nm. The estimated quantum yields were 0.077 and 0.20 at 254 and 222 nm, respectively, similar to the experimental values of 0.078 and 0.19. The simulations also captured distinct initial photodegradation pathways. The first irreversible C-C bond cleavage led to decarboxylation at 254 nm and terminal methyl-group cleavage from the isobutyl side chain at 222 nm. These predicted pathways also aligned well with related experimental observations. The agreement between estimated and experimental results demonstrates TDESMD's potential for simulating UV photolysis of OMPs in water treatment.