Showing papers by "Prashant V. Kamat published in 1986"
TL;DR: In this article, an analogue of chlorophyll a, when adsorbed on colloidal TiO/sub 2/ can participate in the sensitization process by injecting electrons from its excited states into the conduction band of the semiconductor.
Abstract: Chlorophyllin, an analogue of chlorophyll a, when adsorbed on colloidal TiO/sub 2/ can participate in the sensitization process by injecting electrons from its excited states into the conduction band of the semiconductor. Upon excitation in its absorption band, 90% of the fluorescence emission of chlorophyllin could be quenched by colloidal TiO/sub 2/. The apparent association constant for the association between colloidal TiO/sub 2/ and chlorophyllin, as measured from the fluorescence quenching data, was 2 x 10/sup 4/ M/sup -1/. Picosecond lifetime measurements gave the rate constant for the electron injection process from the excited singlet state into the conduction band of the semiconductor as 4.2 x 10/sup 9/ s/sup -1/. The net charge transfer across the sensitizer-semiconductor interface was investigated with the laser flash photolysis and time-resolved microwave absorption techniques. Analysis of the transient absorption spectrum confirmed the generation of the cation radical of chlorphyllin with a quantum yield of 0.015. 32 references, 8 figures, 1 table.
173 citations
TL;DR: In this article, microwave measurements on suspensions of these dye-coated particles have shown large absorption signals when the suspension is irradiated with pulses of 532 nm light from a laser, attributed to mobile charge carriers injected into the TiO2 from the excited singlet state of the dye.
48 citations
TL;DR: Proprietes de l'etat singulet et leetat triplet en solution caracterisees a l'ambiante et 77°K as mentioned in this paper.
Abstract: Proprietes de l'etat singulet et de l'etat triplet en solution caracterisees a l'ambiante et 77°K
10 citations
TL;DR: In this paper, the reduction potentials of radical anion intermediates have been characterized through their electronic spectra, leading to radical anions, which react with oxygen to give superoxide and ultimately products derived through the reaction of superoxide with the starting furanones and bifurandiones.
Abstract: Treatment of furanones (1a – c, 25, 34) and bifurandiones (23, 37) with potassium in THF gave rise to radical anion intermediates, which reacted with oxygen to give superoxide and ultimately products derived through the reaction of superoxide with the starting furanones and bifurandiones. Thus, the reaction of 1a with potassium gave a mixture of 4-oxo-2,2,4-triphenylbutanoic acid (7a), 1,3,3-triphenyl-2-propen-1-one (11a), and benzoic acid (12). The reaction of 11a itself, under similar conditions, gave a mixture of benzophenone (18a) and 12. Similar reactions have been observed in the case of 1b and c. The bifurandione 23, on treatment with potassium, gave a mixture of the 2(5H)-furanone 25, 2,3-diphenylpropenoic acid (31), and 12. The reaction of 25 itself with potassium under similar conditions gave the same mixture of 31 and 12. Treatment of 3-phenyl-2(3H)-benzofuranone (34) with potassium, however, did not give any isolable product; only the starting material could be recovered. Under similar conditions, the bifurandione 37 gave the fragmentation product 34. Cyclic voltammetric studies have been employed to measure the reduction potentials, leading to radical anions, and these intermediates have been characterized through their electronic spectra.
Elektronen-Ubertragungs-Reaktionen. Reaktion von Furanonen und Bifurandionen mit Kalium und Sauerstoff
Bei der Behandlung von Furanonen (1a – c, 25, 34) und Bifurandionen (23, 37) mit Kalium in THF entstehen Radikalanion-Zwischenstufen, die mit Sauerstoff zu Superoxid reagieren, das seinerseits mit den Ausgangsfuranonen und -bifuranonen weiterreagiert. So ergab die Reaktion von 1a mit Kalium eine Mischung von 4-Oxo-2,2,4-triphenylbutansaure (7a), 1,3,3-Triphenyl-2-propen-1-on (11a) und Benzoesaure (12). Unter ahnlichen Bedingungen reagierte 11a selbst zu einer Mischung von Benzophenon (18a) und 12. Ahnliche Ergebnisse wurden im Falle von 1b und c erhalten. Das Bifurandion 23 ergab mit Kalium eine Mischung von 2(5H)-Furanon 25, 2,3-Diphenylpropensaure (31) und 12. 25 selbst reagierte mit Kalium unter ahnlichen Bedingungen zur selben Mischung von 31 und 12. 3-Phenyl-2(3H)-benzofuranon (34) fuhrte mit Kalium jedoch zu keinem isolierbaren Produkt; nur Ausgangsmaterial wurde zuruckgewonnen. Unter vergleichbaren Bedingungen lieferte das Bifurandion 37 das Fragmentierungsprodukt 34. Mit Hilfe der cyclischen Voltammetrie wurden die zu den Radikalanionen fuhrenden Reduktionspotentiale gemessen. Die Radikalanion-Zwischenstufen wurden durch ihre Elektronenspektren charakterisiert.
6 citations
TL;DR: In this article, the reduction potentials of radical anion intermediates have been characterized through their electronic spectra, leading to radical anions, which react with oxygen to give superoxide and ultimately products derived through the reaction of superoxide with the starting furanones and bifurandiones.
Abstract: Treatment of furanones (1a – c, 25, 34) and bifurandiones (23, 37) with potassium in THF gave rise to radical anion intermediates, which reacted with oxygen to give superoxide and ultimately products derived through the reaction of superoxide with the starting furanones and bifurandiones. Thus, the reaction of 1a with potassium gave a mixture of 4-oxo-2,2,4-triphenylbutanoic acid (7a), 1,3,3-triphenyl-2-propen-1-one (11a), and benzoic acid (12). The reaction of 11a itself, under similar conditions, gave a mixture of benzophenone (18a) and 12. Similar reactions have been observed in the case of 1b and c. The bifurandione 23, on treatment with potassium, gave a mixture of the 2(5H)-furanone 25, 2,3-diphenylpropenoic acid (31), and 12. The reaction of 25 itself with potassium under similar conditions gave the same mixture of 31 and 12. Treatment of 3-phenyl-2(3H)-benzofuranone (34) with potassium, however, did not give any isolable product; only the starting material could be recovered. Under similar conditions, the bifurandione 37 gave the fragmentation product 34. Cyclic voltammetric studies have been employed to measure the reduction potentials, leading to radical anions, and these intermediates have been characterized through their electronic spectra.
Elektronen-Ubertragungs-Reaktionen. Reaktion von Furanonen und Bifurandionen mit Kalium und Sauerstoff
Bei der Behandlung von Furanonen (1a – c, 25, 34) und Bifurandionen (23, 37) mit Kalium in THF entstehen Radikalanion-Zwischenstufen, die mit Sauerstoff zu Superoxid reagieren, das seinerseits mit den Ausgangsfuranonen und -bifuranonen weiterreagiert. So ergab die Reaktion von 1a mit Kalium eine Mischung von 4-Oxo-2,2,4-triphenylbutansaure (7a), 1,3,3-Triphenyl-2-propen-1-on (11a) und Benzoesaure (12). Unter ahnlichen Bedingungen reagierte 11a selbst zu einer Mischung von Benzophenon (18a) und 12. Ahnliche Ergebnisse wurden im Falle von 1b und c erhalten. Das Bifurandion 23 ergab mit Kalium eine Mischung von 2(5H)-Furanon 25, 2,3-Diphenylpropensaure (31) und 12. 25 selbst reagierte mit Kalium unter ahnlichen Bedingungen zur selben Mischung von 31 und 12. 3-Phenyl-2(3H)-benzofuranon (34) fuhrte mit Kalium jedoch zu keinem isolierbaren Produkt; nur Ausgangsmaterial wurde zuruckgewonnen. Unter vergleichbaren Bedingungen lieferte das Bifurandion 37 das Fragmentierungsprodukt 34. Mit Hilfe der cyclischen Voltammetrie wurden die zu den Radikalanionen fuhrenden Reduktionspotentiale gemessen. Die Radikalanion-Zwischenstufen wurden durch ihre Elektronenspektren charakterisiert.