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Photoinduced redox properties of cation radicals
78 Photochemistryof indeno[2,1_s]indene
SANG
CHUL
SHIM
and JEONG
SEOK
CHAE
Department of Chemistry, Korea Advanced Institute of Science and Technology, P.O. Box 150, Cheongyangni, Seoul 131 (Korea)
Indeno[2,1_a]indene, a trans-stilbene analogue with a fixed planar configuration, yielded a head-to-head and a head-to-tail C, cyclodimer on direct irradiation with 300 nm UV light. The fluorescence quenching and triplet sensitization studies, solvent effect and temperature effect indicated that the reaction proceeded through a singlet excimer intermediate. The photoreactions of the compound with several olefins which were different in electron affinity were studied. The electron-rich olefins such as 2,3dimethyl-Z-butene and 2,4_cyclohexadiene do not react with indeno[2,1_a]indene. Methyl crotonate and dimethyl isopropylidene malonate yield C4 cycloadducts as major products while dimethyl fumarate gives photoene adduct as a main product. The electron-poor olefin fumaronitrile does not give any photoadducts. The mechanism of the reactions is discussed.
Photoinducedredox propertiesof cation radicals
JEAN-CLAUDE
MOUTET
and GILBERT
REVERDY
DRF-G/Laborutoires de Chimie - EOA (Equipe de Recherche associh au CNRS 675), Centre d’Etudes Nuclkaires de Grenoble. 85 X, 38041 Grenoble CMex (France)
Aromatic amine (e.g. hexametboxydiphenylamine, phenothiazine and tetraphenylbenzidine) cation radicals R-+ are stable in the presence of l,l-diphenylethylene (DPE) and somepara-disubstituted derivatives. Irradiation by visible light (doublet-doublet transitions) initiates an electron transfer leading to the parent compound R and the cation radical DPE*+. Subsequent reactions of DPE.+ on DPE followed by a second electron transfer to R*+ in its ground state and a double deprotonation give rise to a triphenyldihydronaphthalene, a tetraphenyltetrahydrofuran (with water participation) and a tetraphenylbutadiene. The photoinduced electron transfer between R-+ and DPE is the key step but the photoproduct ratio is markedly dependent on dE = E,,,,,DPE - E112dR.+. Alcohols lead to electron transfer with selectively excited R.+ (e.g. benzylic alcohol is converted to benzaldehyde). Electrochemical techniques were used for producing R.+ and for studying photoreactions. Irradiations under controlled potential oxidations of R give rise to photoassisted electrochemical catalytic cycles.
SANG
CHUL
SHIM
and JEONG
SEOK
CHAE
Department of Chemistry, Korea Advanced Institute of Science and Technology, P.O. Box 150, Cheongyangni, Seoul 131 (Korea)
Indeno[2,1_a]indene, a trans-stilbene analogue with a fixed planar configuration, yielded a head-to-head and a head-to-tail C, cyclodimer on direct irradiation with 300 nm UV light. The fluorescence quenching and triplet sensitization studies, solvent effect and temperature effect indicated that the reaction proceeded through a singlet excimer intermediate. The photoreactions of the compound with several olefins which were different in electron affinity were studied. The electron-rich olefins such as 2,3dimethyl-Z-butene and 2,4_cyclohexadiene do not react with indeno[2,1_a]indene. Methyl crotonate and dimethyl isopropylidene malonate yield C4 cycloadducts as major products while dimethyl fumarate gives photoene adduct as a main product. The electron-poor olefin fumaronitrile does not give any photoadducts. The mechanism of the reactions is discussed.
Photoinducedredox propertiesof cation radicals
JEAN-CLAUDE
MOUTET
and GILBERT
REVERDY
DRF-G/Laborutoires de Chimie - EOA (Equipe de Recherche associh au CNRS 675), Centre d’Etudes Nuclkaires de Grenoble. 85 X, 38041 Grenoble CMex (France)
Aromatic amine (e.g. hexametboxydiphenylamine, phenothiazine and tetraphenylbenzidine) cation radicals R-+ are stable in the presence of l,l-diphenylethylene (DPE) and somepara-disubstituted derivatives. Irradiation by visible light (doublet-doublet transitions) initiates an electron transfer leading to the parent compound R and the cation radical DPE*+. Subsequent reactions of DPE.+ on DPE followed by a second electron transfer to R*+ in its ground state and a double deprotonation give rise to a triphenyldihydronaphthalene, a tetraphenyltetrahydrofuran (with water participation) and a tetraphenylbutadiene. The photoinduced electron transfer between R-+ and DPE is the key step but the photoproduct ratio is markedly dependent on dE = E,,,,,DPE - E112dR.+. Alcohols lead to electron transfer with selectively excited R.+ (e.g. benzylic alcohol is converted to benzaldehyde). Electrochemical techniques were used for producing R.+ and for studying photoreactions. Irradiations under controlled potential oxidations of R give rise to photoassisted electrochemical catalytic cycles.