Kuzmin A V, Neumann C, van Wilderen L J G W, Shainyan B A, Bredenbeck J
Institute of Biophysics, Johann Wolfgang Goethe-University, Max-von-Laue-Str. 1, 60438 Frankfurt, Germany.
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Science, 1 Favorsky Str., 664033, Irkutsk, Russian Federation.
Phys Chem Chem Phys. 2016 Mar 28;18(12):8662-72. doi: 10.1039/c5cp07636f.
The photochemistry of p-bromophenylsulfonyl azide (BsN3), p-tolylsulfonyl azide (TsN3) and methylsulfonyl azide (MsN3) was studied by femtosecond time-resolved infrared spectroscopy with CH2Cl2 and CCl4 as solvents along with quantum chemical calculations. The photolysis of these azides after 267 nm light excitation leads to the population of each respective azide S1 excited state. Decay of the S1 excited state gives rise to singlet nitrene formation. In the case of BsN3, the decay was found to correlate with the formation of a pseudo-Curtius photoproduct (PCP) BrC6H4NSO2. Transient electronic ground states of the three azides on their way to singlet nitrenes and PCPs were shown by locating the corresponding transition states on the potential energy surfaces. The lifetime of singlet (1)(BsN) and (1)(TsN) nitrenes is τ(S) = ∼20 ps in CH2Cl2 and ∼700 ps in CCl4. Singlet (1)(MsN) was not detected. Due to fast intersystem crossing (ISC), singlet nitrenes are converted into the triplet spin isomers lying lower in energy, the formation time constants being equal to the corresponding singlet nitrene lifetime. The formation of (3)(MsN) was shown and the formation time constant in CH2Cl2 was found to be τ(ISC) = 34 ± 3 ps. Internal conversion of the S1 excited state to the ground state of the azide was low (Φ ≈ 0.15) for BsN3 and TsN3 and was not found in the case of MsN3.
采用飞秒时间分辨红外光谱法，以二氯甲烷和四氯化碳为溶剂，并结合量子化学计算，研究了对溴苯磺酰叠氮（BsN3）、对甲苯磺酰叠氮（TsN3）和甲基磺酰叠氮（MsN3）的光化学性质。这些叠氮化合物在267 nm光激发后的光解导致各自的叠氮S1激发态的布居。S1激发态的衰变导致单线态氮烯的形成。在BsN3的情况下，发现衰变与假库尔提斯光产物（PCP）BrC6H4NSO2的形成相关。通过在势能面上定位相应的过渡态，展示了三种叠氮化合物在生成单线态氮烯和PCP过程中的瞬态电子基态。单线态（1）（BsN）和（1）（TsN）氮烯在二氯甲烷中的寿命为τ(S) = ∼20 ps，在四氯化碳中为∼700 ps。未检测到单线态（1）（MsN）。由于快速系间窜越（ISC），单线态氮烯转化为能量较低的三线态自旋异构体，形成时间常数等于相应单线态氮烯的寿命。展示了（3）（MsN）的形成，发现在二氯甲烷中的形成时间常数为τ(ISC) = 34 ± 3 ps。对于BsN3和TsN3，S1激发态向叠氮基态的内转换较低（Φ ≈ 0.15），而在MsN3的情况下未发现这种情况。
