期刊
JOURNAL OF PHYSICAL CHEMISTRY A
卷 116, 期 1, 页码 199-206出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp207100q
关键词
-
资金
- FONDECYT-Chile [1110809]
- NSERC
- Becas Chile
- University of Ottawa
We have explored the photogeneration of the coumarin 314 radical cation by using nanosecond laser excitation at wavelengths longer than 400 nm in benzene, acetonitrile, dichloromethane, and aqueous media. In addition, time-resolved absorption spectroscopy measurements allowed detection of the triplet excited state of coumarin 314 (C-314) with a maximum absorption at 550 rim in benzene. The triplet excited state has a lifetime of 90 mu s in benzene. It is readily quenched by oxygen (k(q) = 5.0 x 10(9) M-1 s(-1)). From triplet-triplet energy transfer quenching experiments, it is shown that the energy of this triplet excited state is higher than 35 kcal/mol, in accord with the relatively large singlet oxygen quantum yield (Phi(Delta) = 0.25). However, in aqueous media, the,coumarin triplet was no longer, observed, and instead of that, a long-lived (160 mu s in air equilibrated solutions) free radical cation with a maximum absorbance at 370 nm was detected. The free radical cation generation, which has a quantum yield of 0.2, occurs by electron photoejection. Moreover, density functional theory (DFT) calculations indicate that at least 40% of the electronic density is placed on the nitrogen atom in aqueous media, Which explains its lack of reactivity toward oxygen. On the Other. hand, rate constant values close to the diffusion rate limit in water (>10(9) M-1 s(-1)) were found for the quenching of the C-314 free radical cation by phenolic antioxidants. The results have been interpreted by an electron transfer reaction between the Phenolic antioxidant and the radical cation where ion pair formation could be involved.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据