Direct Observation of a Sulfonyl Azide Excited State and Its Decay Processes by Ultrafast Time-Resolved IR Spectroscopy

摘要

The photochemistry of 2-naphthylsulfonyl azide (2-NpSO_2N_3) was studied by femtosecond time-resolved infrared (TR-IR) spectroscopy and with quantum chemical calculations. Photolysis of 2-NpSO_2N_3 with 330 nm light promotes 2-NpSO_2N_3 to its S_1 state. The S_1 excited state has a prominent azide vibrational band. This is the first direct observation of the S_1 state of a sulfonyl azide, and this vibrational feature allows a mechanistic study of its decay processes. The S_1 state decays to produce the singlet nitrene. Evidence for the formation of the pseudo-Curtius rearrangement product (2-NpNSO_2) was inconclusive. The singlet sulfonylnitrene ~1(2-NpSO_2N) is a short-lived species (t ≈ 700 ± 300 ps in CC1_4) that decays to the lower-energy and longer-lived triplet nitrene ~33(2-NpSO_2N). Internal conversion of the S_1 excited state to the ground state S_0 is an efficient deactivation process. Intersystem crossing of the S_1 excited state to the azide triplet state contributes only modestly to deactivation of the S_1 state of 2-NpSO_2N_3.