Ultrafast Photodissociation and Recombination Dynamics of Methyl p-Tolyl Sulfoxide in Solution: Insights from Transient Absorption Spectroscopy and Computational Studies

When molecular fragmentation takes place in solution, solute-solvent interactions introduce additional pathways for radical recombination and secondary chemical transformations, adding complexity to the photodissociation dynamics in comparison to the dynamics observed in isolated systems. In this study, we investigate the ultrafast photodynamics of methyl p-tolyl sulfoxide (Metoso) in the 1-300 ps time range in dimethyl sulfoxide and ethanol solutions using ultrafast transient absorption spectroscopy. Density functional theory calculations have assisted in the interpretation of the experimental data. Upon UV irradiation, Metoso undergoes homolytic cleavage of one of the sulfur-carbon (S-CH3) bonds, leading to the formation of methyl and para tolylsulfinyl radicals. We explore the competition between geminate recombination, diffusional separation, and alternative reaction pathways. Our results provide insights into the early-stage photochemistry of alkyl-aryl sulfoxides, highlighting the role of solvent interactions influencing radical lifetimes, recombination, and reaction dynamics. These findings contribute to a deeper understanding of sulfoxide photoreactivity, which is relevant to medicinal chemistry and organic synthesis.