Photosensitized Oxygenation as a Function of the Triplet Energy of Sensitizers*

Gollnick, Klaus; Franken, Theodor; Schade, G.; Dörhöfer, Günther

doi:10.1111/j.1749-6632.1970.tb39307.x

Cited by 144 publications

(40 citation statements)

References 28 publications

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“…It follows that the involvement of 1 O 2 * can be ruled out because we have found no photoisomerization enhancement of any kind under triplet-sensitized conditions in air-saturated AN (9). As a further precaution, we now report that addition of 0.188 M 2,5-dimethylfuran (DMF), a very efficient 1 O 2 * scavenger (28,41), has no effect on the φ ctt : φ tct ratio in air-saturated AN.…”

Section: Oxygen Effects On Ttt-dph Photoisomerizationmentioning

confidence: 92%

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Saltiel¹,

Krishnamoorthy²,

Huang³

et al. 2003

Can. J. Chem.

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Irradiation of all-trans-1,6-diphenyl-1,3,5-hexatriene (ttt-DPH) in degassed acetonitrile (AN) gives ctt-and tct-DPH, relatively inefficiently, mainly via isomerization in the singlet excited state. The triplet contribution to the photoisomerization is small due to a very low intersystem crossing yield (φ is = 0.01). Central bond isomerization is quenched in the presence of air by a factor of 1.4, consistent with the expected quenching of the lowest singlet and triplet excited states by oxygen. However, the presence of air enhances terminal bond photoisomerization by nearly twofold. Triplet-sensitized ttt-DPH photoisomerization favors tct-DPH formation and is quenched by oxygen. It follows that the interaction of singlet-excited ttt-DPH with O 2 suppresses isomerization to tct-DPH but opens a new isomerization pathway to ctt-DPH. The presence of dimethylfuran, a singlet O 2 trap, has no effect on the photoisomerization, eliminating the possible involvement of singlet O 2 in this new reaction. ttt-DPH radical cations are ruled out as intermediates because the presence of fumaronitrile, which leads to their formation, suppresses both central and terminal bond photoisomerizations. In contrast to acetonitrile, ctt-DPH formation is quenched by oxygen in methylcyclohexane, suggesting the requirement of a polar environment. Strikingly different deuterium isotope effects distinguish the direct and O 2 -induced photoisomerization pathways. A comparative study of ttt-DPH-d 0 with ttt-DPH-d 2 and ttt-DPH-d 4 , involving deuteration of one and both terminal double bonds, reveals an inverse kinetic isotope effect (k H ox /k D ox = 0.92) for the O 2 -induced reaction. An attractive mechanism for the new oxygen-induced photoisomerization involves charge transfer from the S 1 state of ttt-DPH to oxygen followed by collapse of the exciplex to either a zwitterionic or a biradicaloid species through bonding at one of the benzylic positions. Rotation about the new single bond in this intermediate followed by reversion to DPH and O 2 gives the observed result. 679Résumé : L'irradiation du 1,6-diphénylhexa-1,3,5-triène complètement trans (ttt-DPH), dans de l'acétonitrile dégazé (AN) conduit d'une façon relativement inefficace à la formation des ctt-et tct-DPH, principalement par le biais d'une isomérisation dans l'état excité singulet. La contribution triplet à la photoisomérisation est faible en raison du très faible rendement du passage intersystème (φ is = 0,01). L'isomérisation de la liaison centrale est piégée en présence d'air par un facteur de 1,4 qui est en accord le piégeage par l'oxygène des états excités singulet et triplet les plus bas. Toutefois, la présence d'air augmente la photoisomérisation de la liaison terminale par un facteur égal pratiquement à deux. La photoisomérisation du ttt-DPH sensibilisée au niveau triplet favorise la formation de tct-DPH et elle est piégée par l'oxygène. Il en découle que l'interaction de l'oxygène avec le ttt-DPH excité à l'état singulet supprime l'isomérisation en tct-DPH mais qu'elle co...

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Section: Oxygen Effects On Ttt-dph Photoisomerizationmentioning

confidence: 92%

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Saltiel¹,

Krishnamoorthy²,

Huang³

et al. 2003

Can. J. Chem.

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“…Experimentally, the lowest excited electronic state of molecular oxygen (3~ < IA) lies 22.5 kcal mole -1 above the ground state [14]. This suggests that most organic molecules (PCBs in this work) can sensitize (photochemically) the formation of 102 (reaction (3)) [16]. Compounds with triplet states greater than 37.5 kcal mole 1 (3~ < 1~) lead to the formation of l~g+ (02) which, in solution, is rapidly quenched to the Ag state [17].…”

Section: Theorymentioning

confidence: 94%

Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

et al. 2000

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SummaryThe parameters effecting the sensitivity and selectivity of a photochemical reaction detection scheme based on the reaction of 3-substituted pyrroles with singlet molecular oxygen (102) in HPLC are reported. Polychlorinated biphenyls (PCBs) were chosen as model compounds for the detection scheme. Following separation by reverse-phase chromatography, PCBs are excited by a Hg pen-ray lamp in a crocheted PTFE photochemical reactor. PCBs that are efficient 102-sensitizers promote ground state 02 (3~g_) to an excited state (l~g § or lAg) which rapidly oxidizes 3-substituted pyrroles which are added to the mobile phase. Detection is based on the loss ofpyrrole. The reaction is catalytic in nature since one analyte molecule may absorb light many times, producing large amounts of 102. Detection limits for 4,4'-dichlorobiphenyl and Aroclors 1242, 1248 and 1254 were improved by 1-2 orders of magnitude over optimized UV-absorbance detection. Configuration of the photochemical reactor and judicious choice of the wavelength used to follow the loss of pyrrole were determined to be the most important factors in terms of sensitivity of the detection scheme. Comparison of three reagents (i.e. 3-substituted-pyr-1 roles) used for trapping 02 demonstrates the effect of substitution on sensitivity and to some extent selectivity of PCB determination.

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“…34 Photolyzed Rose Bengal in the presence of the reference fulvic acids resulted in a substantial increase (5 times) in the observed degradation coefficient for OMP. Whereas the addition suggests susceptibility of OMP to singlet oxygen, it does not conclusively demonstrate singlet oxygen involvement.…”

Section: Journal Of Agricultural and Food Chemistrymentioning

confidence: 97%

Photodegradation of Ormetoprim in Aquaculture and Stream-Derived Dissolved Organic Matter

Guerard

Chin

2012

J. Agric. Food Chem.

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Ormetoprim (OMP) is an antibiotic approved for use in the United States to prevent the spread of disease in freshwater aquaculture. It has been shown in the previous literature to be photochemically stable to direct photolysis, but the role of photosensitization processes in the presence of dissolved organic matter (DOM) on the rate of degradation is not well understood. The present results show that water and DOM (specifically the fulvic acid fraction) isolated from a eutrophic aquaculture catfish pond and a nearby stream (Deer Creek) at the Mississippi State University Delta Research and Extension Center facility in Stoneville, MS, significantly increased the phototransformation of OMP relative to direct photolysis. Similar results were reported for reference fulvic acids obtained from the International Humic Substances Society. Results from a combination of scavenging experiments and experiments conducted under anoxic conditions indicate the indirect photodegradation pathway occurs by hydroxyl radical, singlet oxygen attack, and reaction with triplet excited-state DOM.

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Photosensitized Oxygenation as a Function of the Triplet Energy of Sensitizers*

Cited by 144 publications

References 28 publications

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

Photodegradation of Ormetoprim in Aquaculture and Stream-Derived Dissolved Organic Matter

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Photosensitized Oxygenation as a Function of the Triplet Energy of Sensitizers*

Cited by 144 publications

References 28 publications

Stereoselective O2-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Stereoselective O2-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

Photodegradation of Ormetoprim in Aquaculture and Stream-Derived Dissolved Organic Matter

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Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene

Stereoselective O₂-induced photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene