An Ultrafast Infrared and UV–Vis Study of the Photochemistry of 2-Naphthaloxycarbonyl Azide

The photochemistry and photophysics of 2-naphthaloxycarbonyl azide was studied in solution at ambient temperature with femtosecond (fs) time-resolved infrared (IR) and UV-vis spectroscopic methods. An upper singlet excited state of the azide, S_n (<i>n</i> > 1), decays by three processes: relaxation to azide S₁, nitrogen extrusion and formation of the singlet nitrene, and fragmentation to form the ·OCN₃ and 2-NpO· radicals. The decay of the S₁ state of the azide correlates with 3-isocyanatonaphthalen-2(3<i>H</i>)-one formation, which, in turn, slowly converts to 3-isocyanatonaphthalen-2-ol. The singlet nitrene decays by intersystem crossing (ISC) to produce the corresponding triplet nitrene with a time constant of ∼100 ps. The results are consistent with prior electron spin resonance and ultrafast time-resolved experiments positing that the lowest-energy singlet state of aryloxycarbonylnitrenes is closed-shell and that the singlet state undergoes rapid ISC via spin-orbit coupling to the triplet ground state.