Photoexcitation Dynamics of V-PYRRO/NO Investigated Using Femtosecond Time-Resolved Infrared Spectroscopy

Diazeniumdiolates spontaneously release nitric oxide (NO) in aqueous solutions. Therefore, protected diazeniumdiolates have been developed for the controlled administration of NO to specific targets. Diazeniumdiolates with photoprotecting groups are useful for spatiotemporal NO delivery. To develop photoactivated NO donors, understanding the photodissociation dynamics of photoprotected diazeniumdiolates is essential. The dynamics of photoexcited V-PYRRO/NO (a well-studied liver-selective NO prodrug) was investigated to understand the photodissociation mechanism of protected diazeniumdiolates at the molecular level. Upon excitation at 305 nm, the N═N bond of V-PYRRO/NO was cleaved within 0.3 ps, producing N-nitrosopyrrolidine and CH₂═CHON. CH₂═CHON, the first oxynitrene directly observed in the solution in real-time, was formed in the singlet state and rearranged into CH₂═CHNO with a time constant of 16 ± 5 ns. The calculated potential energy surfaces of the excited states confirmed the unusual breakage of the N═N bond. The findings can be utilized to develop more effective photoactivated diazeniumdiolates.