Ultrafast laser spectroscopic study on the electronic properties and reactivity of phenyloxenium ions

Phenyloxenium ions are reactive intermediates of formula R-O+. These species are the isoelectronic oxygen analog of the more familiar nitrene class of intermediates, but bear a formal positive charge on a hypovalent oxygen. The phenylnitrenium ion and benzyl cation have been deeply studied theoretical computations and characterized by the time-resolved spectroscopies. Although oxenium ions are often important reactive intermediates in synthetic chemistry and enzymology, the lack of general methods to photogenerate these species has hindered their study by directly detecting and studying their chemical reactivities, lifetimes, spectroscopic signatures and electronic configurations. In addition, the free of oxenium ion is a very short-lived species in the solution; the traditional methods can not take a snapshot it. Therefore, ultrafast time-resolved spectroscopies are required to capture these short-lived intermediates. Recent, we used selected protonated hydroxylamine salts as novel photoprecursors to generate the singlet ground state parent phenyloxenium ion, the open shell singlet and triplet biphenylyl oxenium ion and ground state triplet ground state phenyloxenium ion as a product from the photoheterolysis of the aryl hydroxylamine tetrafluoroborate salt.1,3 A combination of femtosecond and nanosecond transient absorption spectroscopy, nanosecond time-resolved Resonance Raman spectroscopy (ns-TR3), cryogenic matrix EPR spectroscopy, computational analysis, and photoproduct studies allowed us to trace essentially the complete arc of the photophysics and photochemistry of this photoprecursor and permitted a first look at these oxenium ions.