Photoreduction of Oxoisoaporphines by Amines: Laser Flash and Steady-State Photolysis, Pulse Radiolysis, and TD-DFT Studies

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• 作者：Julio R. De la Fuente ; Christian Aliaga ; Cristian Poblete ; Gerald Zapata ; Carolina Jullian ; Claudio Saitz ; Alvaro Caete ; Gabriel Kciuk ; Eduardo Sobarzo-Sanchez ; Krzysztof Bobrowski
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：July 9, 2009
• 年：2009
• 卷：113
• 期：27
• 页码：7737-7747
• 全文大小：241K
• 年卷期：v.113,no.27(July 9, 2009)
• ISSN：1520-5215

文摘

Photoreduction of oxoisoaporphine (OIA) (1-aza-benzo-[de]anthracen-7-one) and its 5-methoxy (5-MeO-OIA) derivative by selected amines (two non-α-hydrogen-donating amines (1,4-diaza[2.2.2]-bicyclooctane (DABCO) and 2,2,6,6-tetramethylpiperidine (TMP)) and three α-hydrogen-donating amines (triethylamine (TEA), diethylmethylamine (DEMA), and dimethylethylamine (DMEA))) has been studied in deaerated neat acetonitrile solutions using laser flash and steady-state photolysis. The triplet excited states of OIA and 5-MeO-OIA are characterized by intense absorption maxima located at λ_max = 450 nm and lifetimes of 34.7 ± 0.5 and 44.6 ± 0.4 μs, respectively. In the presence of tertiary amines, both triplets are quenched with a rate constant that varies from the near diffusion limit (>10⁹ M⁻¹ s⁻¹) to a rather low value (10⁷ M⁻¹ s⁻¹) and shows the expected dependence on the reduction potential for one-electron-transfer reactions. The transient absorption spectra observed after quenching of the respective triplet states are characterized by distinct absorption maxima located at λ_max = 480 and 490 nm (for OIA and 5-MeO-OIA, respectively) and accompanied by broad shoulders in the range of 510−560 nm. They were assigned to either solvent-separated radical ion pairs and/or isolated radical anions. In the presence of α-hydrogen-donating amines these species undergo protonation that leads to the formation of neutral hydrogenated radicals A1H^•/A2H^• with two possible sites of protonation, N and O atoms. Pulse radiolysis and molecular modeling together with TD-DFT calculations were used to support the conclusions about the origin of transients.