Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
J Am Chem Soc. 2011 Jun 29;133(25):9751-61. doi: 10.1021/ja109098w. Epub 2011 Jun 2.
The photochemistry of 2-naphthoyl azide was studied in various solvents by femtosecond time-resolved transient absorption spectroscopy with IR and UV-vis detection. The experimental findings were interpreted with the aid of computational studies. Using polar and nonpolar solvents, the formation and decay of the first singlet excited state (S(1)) was observed by both time-resolved techniques. Three processes are involved in the decay of the S(1) excited state of 2-naphthoyl azide: intersystem crossing, singlet nitrene formation, and isocyanate formation. The lifetime of the S(1) state decreases significantly as the solvent polarity increases. In all solvents studied, isocyanate formation correlates with the decay of the azide S(1) state. Nitrene formation correlates with the decay of the relaxed S(1) state only upon 350 nm excitation (S(0) → S(1) excitation). When S(n) (n ≥ 2) states are populated upon excitation (λ(ex) = 270 nm), most nitrene formation takes place within a few picoseconds through the hot S(1) and higher singlet excited states (S(n)) of 2-naphthoyl azide. The data correlate with the results of electron density difference calculations that predict nitrene formation from the higher-energy singlet excited states, in addition to the S(1) state. For all of these experiments, no recovery of the ground state was observed up to 3 ns after photolysis, which indicates that both internal conversion and fluorescence have very low efficiencies.
通过飞秒时间分辨瞬态吸收光谱技术结合红外和紫外可见检测，研究了 2-萘甲酰叠氮在不同溶剂中的光化学性质。借助计算研究对实验结果进行了解释。使用极性和非极性溶剂，通过时间分辨技术观察到了第一单重激发态（S(1)）的形成和衰减。2-萘甲酰叠氮的 S(1)激发态的衰减涉及三个过程：系间窜越、单线态氮烯形成和异氰酸酯形成。S(1)态的寿命随着溶剂极性的增加而显著降低。在所研究的所有溶剂中，异氰酸酯的形成与叠氮 S(1)态的衰减相关。只有在 350nm 激发（S(0)→S(1)激发）时，氮烯的形成才与松弛的 S(1)态的衰减相关。当 S(n)（n≥2）态在激发时（λ(ex)=270nm）被激发时，大多数氮烯的形成在几皮秒内通过 2-萘甲酰叠氮的热 S(1)态和更高的单线态激发态（S(n)）发生。这些数据与电子密度差计算的结果相关联，该计算预测了氮烯的形成来自于更高能量的单线态激发态，以及 S(1)态。对于所有这些实验，在光解后 3ns 内没有观察到基态的恢复，这表明内转换和荧光的效率非常低。
