Production of singlet molecular oxygen from the oxygen quenching of the lowest excited singlet state of aromatic molecules in n-hexane solution

Wu, K.; Trozzolo, A. M.

doi:10.1021/j100487a023

Cited by 46 publications

(22 citation statements)

References 7 publications

(8 reference statements)

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“…10 O 2 deactivates the DPH triplets by energy transfer because, in attenuating the triplet lifetime 1000-fold (∼60 µs to ∼100 ns), 9,11 it is converted efficiently to O 2 ( 1 ∆ g ). 12,13 It follows that O 2 quenching provides a snapshot of the DPH triplet conformer distribution. 10 The DPH triplet potential energy surface that was proposed to account for the observations is about 34 kcal/mol higher in energy than the all-trans ground-state global minimum 14 and has very shallow minima at 3 ttt*, 3 tct*, 3 ctt*, and 3 cct* conformations that differ from the corresponding groundstate isomers mainly in bond lengths and ease of interconversion.…”

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

et al. 2010

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The 1,6-diphenyl-1,3,5-hexatriene (DPH) triplet decay rate constant in degassed benzene is strongly temperature-dependent. Photostationary states for the fluorenone-sensitized photoisomerization of DPH in degassed methylcyclohexane (MCH) favor the all-trans isomer and become richer in the cis isomers as the temperature is increased. The results are interpreted in terms of competing decays from equilibrated triplet conformers on the basis of the experimentally derived DPH triplet potential energy surface [Saltiel, J.; Crowder, J. M.; Wang, S. J. Am. Chem. Soc. 1999, 121, 895 902; 5352]. Calculated geometries and energy differences [B3LYP/6-311+G(d,p)] are consistent with the experimental model.

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Section: Introductionmentioning

confidence: 99%

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

et al. 2010

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“…The possibility that O 2 opens a thermal free radical isomerization process can be ruled out because the observed (28,29). 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).…”

Section: Oxygen Effects On Ttt-dph Photoisomerizationmentioning

confidence: 78%

“…Energy transfer from the triplet state of ttt-DPH to O 2 in air-saturated solutions yields O 2 *( 1 ∆ g ) with unit efficiency (28). Quenching of the singlet state of ttt-DPH leads to O 2 *( 1 ∆ g ) less efficiently and the efficiency decreases with increasing solvent polarity (0.5 and 0.3 in cyclohexane and methanol, respectively) (29).…”

Section: Introductionmentioning

confidence: 99%

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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“…Other O 2 -induced processes may occur as competing processes, e.g. singulet oxygen formation or photoisomerization [42]. These processes, with the CCT complex formation as main reaction are described as oxygen quenching, (Q).…”

Section: Resultsmentioning

confidence: 99%

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex

Hunger¹,

Kleinermanns²

2013

OJPC

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The fluorescence kinetics of 1,6-diphenyl-1,3,5-hexatriene (DPH) dissolved in cyclohexane was investigated as a function of temperature, concentration and 355 nm excitation pulse energy. At concentrations above 2.5 μM and excitation energies above 1 mJ a long-lived, very intense emission, which appears within less than 5 ns and lasts up to 70 ns, is observed. During the first 50 ns the decay does not follow an exponential but rather a linear behaviour. In oxygen saturated solutions the long-lived emission is suppressed and solely short-lived fluorescence with τ < 5 ns can be detected. A kinetic simulation was performed, based on a model whereupon the long-lived emission originates from the S 1 -state and competes with the formation of DPH-O 2 contact charge-transfer complexes and intersystem crossing which both quench the fluorescence. Our investigations show that even the small amount of oxygen dissolved in nitrogen saturated solutions has a distinct influence on the fluorescence kinetics of DPH.

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Production of singlet molecular oxygen from the oxygen quenching of the lowest excited singlet state of aromatic molecules in n-hexane solution

Cited by 46 publications

References 7 publications

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

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

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex

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Production of singlet molecular oxygen from the oxygen quenching of the lowest excited singlet state of aromatic molecules in n-hexane solution

Cited by 46 publications

References 7 publications

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

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

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S&lt;sub&gt;1&lt;/sub&gt;-State Competes with Formation of O&lt;sub&gt;2&lt;/sub&gt; Contact Charge Transfer Complex

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

Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S<sub>1</sub>-State Competes with Formation of O<sub>2</sub> Contact Charge Transfer Complex