title: Time-resolved resonance Raman and computational investigation of the influence of 4-acetamido and 4-N-methylacetamido substituents on the chemistry of phenylnitrene.
abstract: A time-resolved resonance Raman (TR(3)) and computational investigation of the photochemistry of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide in acetonitrile is presented. Photolysis of 4-acetamidophenyl azide appears to initially produce singlet 4-acetamidophenylnitrene which undergoes fast intersystem crossing (ISC) to form triplet 4-acetamidophenylnitrene. The latter species formally produces 4,4'-bisacetamidoazobenzene. RI-CC2/TZVP and TD-B3LYP/TZVP calculations predict the formation of the singlet nitrene from the photogenerated S(1) surface of the azide excited state. The triplet 4-acetamidophenylnitrene and 4,4'-bisacetamidoazobenzene species are both clearly observed on the nanosecond to microsecond time-scale in TR(3) experiments. In contrast, only one species can be observed in analogous TR(3) experiments after photolysis of 4-N-methylacetamidophenyl azide in acetonitrile, and this species is tentatively assigned to the compound resulting from dimerization of a 1,2-didehydroazepine. The different photochemical reaction outcomes for the photolysis of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide molecules indicate that the 4-acetamido group has a substantial influence on the ISC rate of the corresponding substituted singlet phenylnitrene, but the 4-N-methylacetamido group does not. CASSCF analyses predict that both singlet nitrenes have open-shell electronic configurations and concluded that the dissimilarity in the photochemistry is probably due to differential geometrical distortions between the states. We briefly discuss the probable implications of this intriguing substitution effect on the photochemistry of phenyl azides and the chemistry of the related nitrenes.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, People's Republic of China.
authors.forename: Jiadan
authors.initials: J
authors.lastname: Xue
authors.forename: Shubham
authors.initials: S
authors.lastname: Vyas
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.forename: Hoi Ling
authors.initials: HL
authors.lastname: Luk
authors.forename: Yung Ping
authors.initials: YP
authors.lastname: Chuang
authors.forename: Tracy Yuen Sze
authors.initials: TY
authors.lastname: But
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Toy
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.forename: Arthur H
authors.initials: AH
authors.lastname: Winter
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Hadad
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Platz