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1.
Chemphyschem ; 11(12): 2594-605, 2010 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-20677312

RESUMO

Electron donor (D) substituted 3-ethoxycarbonylcoumarin (CM) derivatives [D-CM: D = 4-diphenylaminophenyl (DPA), 4-diethylaminophenyl (DEA), 4-dimethylaminophenyl (DMA), and 2-methyl-4-dimethylaminophenyl (MeDMA)] are synthesized and characterized. Photoinduced electron transfer (ET) from the D moiety to the acceptor (CM) and back electron transfer (BET) are investigated by femtosecond and nanosecond laser flash photolysis measurements. Femtosecond laser excitation at 355 nm of a deaerated acetonitrile (MeCN) solution of D-CM shows generation of the singlet charge-separated (CS) state [(1)(D(.+)-CM(.-))] by ET from D to the singlet excited state of the CM moiety ((1)CM*), and this is followed by rapid decay within 3 ns to afford the triplet excited state (D-(3)CM*). Nanosecond laser excitation of a deaerated MeCN solution of D-CM results in formation of the triplet CS state by ET from D to (3)CM*. The quantum yield of formation of the triplet CS state [(3)(DPA(.+)-CM(.-))] in the presence of iodobenzene (PhI) in deaerated MeCN increases with increasing concentration of PhI to reach 27 % at 0.5 M PhI. The triplet CS state decays by bimolecular BET because of the long CS lifetime by unimolecular BET. Formation of the long-lived triplet CS state was confirmed by electron spin resonance (ESR) measurements. The photorobust nature of DPA-CM is demonstrated by multiple laser pulse excitation (>1000 times) at 355 nm. The photoinduced ET and BET rate constants of a series of D-CM are thoroughly analyzed in light of the Marcus theory of electron transfer.


Assuntos
Cumarínicos/química , Elétrons , Fotólise , Cumarínicos/síntese química , Cristalografia por Raios X , Transporte de Elétrons , Modelos Moleculares , Oxirredução , Fotoquímica
2.
Org Lett ; 7(19): 4265-8, 2005 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-16146403

RESUMO

[reaction: see text] Photocatalytic oxygenation of tetraphenylethylene (TPE) with oxygen occurs efficiently via electron-transfer reactions of TPE and oxygen with a photogenerated electron transfer state of 9-mesityl-10-methylacridniium ion, followed by the radical-coupling reaction between TPE radical cation and O2*- to produce 1,2-dioxetane selectively. The further photocatalytic cleavage of the O-O bond of dioxetane affords benzophenone as the final oxygenated product.


Assuntos
Alcenos/química , Elétrons , Compostos Heterocíclicos/química , Oxigênio/química , Benzofenonas/química , Catálise , Compostos Heterocíclicos com 1 Anel , Modelos Moleculares , Estrutura Molecular , Fotoquímica , Análise Espectral
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