Photochemistry of Hypervalent Iodoazide Derivatives

The photochemical properties and reaction mechanisms of a series of hypervalent iodoazide compounds (R-IN₃) were investigated, with substituents (-CH₃, -H, -CF₃) tuning the electronic density of the phenyl ring. With the help of UV irradiation, ultrafast time-resolved spectroscopy, and density functional theory (DFT) calculations, we elucidated the mechanisms of azide radical (N₃^•) release and its subsequent reactivity. UV-vis spectroscopy reveals that the photoconversion rates follow the trend CH₃ > H > CF₃, aligning with DFT-calculated ΔG values for ring-opening transitions. Homolytic cleavage of the I-N bond is identified as the dominant pathway for N₃^• generation upon UV irradiation, occurring within 400 fs. The released azide radicals react with the solvent molecules, while the iodo radical R-I_C^• fragments undergo a thermodynamically uphill lactone ring-opening (RO) reaction and subsequent hydrogen atom abstraction from the solvent to form carboxylic acids R-I-COOH, as validated by NMR and IR spectroscopy. The study also highlights the role of substituents in influencing reaction kinetics and intermediate stability, with electron-donating groups accelerating the release of the N₃^• species. This work bridges experimental observations with computational predictions, offering a foundation for future advancements in azide-based reactions and materials.