Ultrafast Spectroscopy and Computational Study of the Photochemistry of Diphenylphosphoryl Azide: Direct Spectroscopic Observation of a Singlet Phosphorylnitrene

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• 作者：Shubham Vyas ; Sivaramakrishnan Muthukrishnan ; Jacek Kubicki ; Ryan D. McCulla ; Gotard Burdzinski ; Michel Sliwa ; Matthew S. Platz ; Christopher M. Hadad
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：December 1, 2010
• 年：2010
• 卷：132
• 期：47
• 页码：16796-16804
• 全文大小：438K
• 年卷期：v.132,no.47(December 1, 2010)
• ISSN：1520-5126

文摘

The photochemistry of diphenylphosphoryl azide was studied by femtosecond transient absorption spectroscopy, by chemical analysis of light-induced reaction products, and by RI-CC2/TZVP and TD-B3LYP/TZVP computational methods. Theoretical methods predicted two possible mechanisms for singlet diphenylphosphorylnitrene formation from the photoexcited phosphoryl azide. (i) Energy transfer from the (π,π*) singlet excited state, localized on a phenyl ring, to the azide moiety, thereby leading to the formation of the singlet excited azide, which subsequently loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. (ii) Direct irradiation of the azide moiety to form an excited singlet state of the azide, which in turn loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. Two transient species were observed upon ultrafast photolysis (260 nm) of diphenylphosphoryl azide. The first transient absorption, centered at 430 nm (lifetime (τ) 28 ps), was assigned to a (π,π*) singlet S₁ excited state localized on a phenyl ring, and the second transient observed at 525 nm (τ 480 ps) was assigned to singlet diphenylphosphorylnitrene. Experimental and computational results obtained from the study of diphenyl phosphoramidate, along with the results obtained with diphenylphosphoryl azide, supported the mechanism of energy transfer from the singlet excited phenyl ring to the azide moiety, followed by nitrogen extrusion to form the singlet phosphorylnitrene. Ultrafast time-resolved studies performed on diphenylphosphoryl azide with the singlet nitrene quencher, tris(trimethylsilyl)silane, confirmed the spectroscopic assignment of singlet diphenylphosphorylnitrene to the 525 nm absorption band.