Photoinduced Intramolecular Proton Transfer and Intermolecular Hydrogen-Atom Abstraction of 1-Piperidinoantraquinone (PAQ)

Nakayama, Toshihiro; Nagai, Nobuaki; Torii, Yukiyoshi; Hamanoue, Kumao

doi:10.1246/cl.1999.33

Cited by 1 publication

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“…On the basis of the present study, the tentative assignment of band A to the absorption due to the lowest excited singlet state of NIR 1 as well as estimation of the shift time (∼10 ns) of band A reported in the previous Letter are incorrect.…”

Section: Referencescontrasting

confidence: 78%

Excited-State Dynamics of 1-Piperidino- or 1-Pyrrolidino-anthraquinone for Formation of N−Ylide and Reduced Compounds

et al. 2000

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By means of subpicosecond laser photolysis of the title compound at room temperature, time-dependent shift of an absorption band has been observed at short delay times which is ascribed to solvent reorganization around the lowest excited singlet state of the solute molecule with an intramolecular charge-transfer character. In comparison with the results obtained by nanosecond laser photolysis and steady-state photolysis at 77 K, it is concluded that the lowest excited singlet state undergoes rapid intramolecular proton transfer forming an N-ylide compound. For formation of the N-ylide compound from the lowest excited singlet state of 1-piperidino-anthraquinone, it is considered that there exists an intermediate which can be ascribed to transfer of the equatorial proton to the carbonyl oxygen anion. At room temperature, no formation of N-ylide compound as a stable compound can be observed due to its rapid reversion to 1-piperidino- or 1-pyrrolidino-anthraquinone. Steady-state photolysis in ethanol at room temperature gives rise to formation of a reduced compound. Yield of the reduced compound is obtained by 405 or ≥510 nm photolysis, however, is negligibly small compared with that obtained by 313 or 366 nm photolysis. Hence, it is proposed that intersystem crossing from a higher excited singlet state (probably the second excited singlet state) to a higher excited triplet state (probably the third excited triplet state) followed by internal conversion to the lowest excited triplet (T1) state plays an important role for the photoreduction, i.e., the reduced compound may be formed from the T1 state, although the possibility of additional photoreduction originating from the second excited triplet state cannot be ruled out.

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Section: Referencescontrasting

confidence: 78%