Effect of cyclodextrin complexation on the photochemistry of p-methoxy-β-phenylpropiophenone

Netto‐Ferreira, José Carlos; Scaiano, J. C.

doi:10.1016/1010-6030(88)80120-5

Cited by 16 publications

(6 citation statements)

References 11 publications

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“…Cupric ions have been employed for quenching studies in microheterogeneous media, ,, and we employed this cationic quencher to study the mobility of xanthone associated with bile salt aggregates. The quenching rate constant for triplet xanthone in aqueous solution was (5.7 ± 0.3) × 10 7 M -1 s -1 , the same value within experimental error as previously determined in our group .…”

Section: Resultsmentioning

confidence: 99%

Dynamics of Probe Complexation to Bile Salt Aggregates

1996

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Excited triplet naphthalene and xanthone were employed as probe molecules to study the dynamics of incorporation into sodium cholate, taurocholate, and deoxycholate aggregates. The association and dissociation rate constants and the quenching rate constants for the incorporated probes were recovered from the dependence of the observed triplet decay rate constants on quencher concentrations (nitrite and cupric ions). Triplet naphthalene was incorporated into a site offering a high degree of protection from quenchers and from which dissociation was relatively slow. Triplet xanthone was incorporated into a less protected site from which dissociation was an order of magnitude faster than from the naphthalene site. We propose that naphthalene was incorporated into the hydrophobic site of primary aggregates, and xanthone was located in the region containing the hydroxyl groups in the secondary aggregates.

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Section: Resultsmentioning

confidence: 99%

Dynamics of Probe Complexation to Bile Salt Aggregates

1996

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“…Much of the research in this field has been concerned with control of photoreactions as outlined in a number of review articles. − The emphasis has mainly been placed on intramolecular transformations but some attention has also been given to intermolecular events. A large number of reports have also appeared addressing the issue of cyclodextrin control of the photophysical quenching processes involving singlet excited states of guest molecules. ,,− By contrast, triplet excited state processes have attracted less attention. ,− The few studies to appear have involved triplets reacting with the cyclodextrin cavity itself, ,, experiencing intramolecular quenching, , or being able to probe the rate of exit from the CD cavity. , While some of these reports discuss bimolecular triplet quenching, there is clearly rather little information available on how CD complexation influences intermolecular photoprocesses of triplet states. The present contribution addresses this deficit.…”

Section: Introductionmentioning

confidence: 99%

Bimolecular Processes of α-Terthiophene in a β-Cyclodextrin Environment: An Exploratory Study

et al. 1996

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The photophysics of triplet excited R-terthiophene (RT) is investigated in the absence and presence of -cyclodextrin ( -CD). Adding -CD to an aqueous RT solution causes the ground state terthiophene to form an inclusion complex with the cyclodextrin molecule. This host/guest complex has a 1:1 stoichiometry with an association constant K ) 5850 ( 230 M -1 . With no added -CD, the RT triplet in aqueous methanol decays with a decay time ) 80 µs. Adding -CD increases the decay time of the triplet to approximately 100 µs. The decay in the compartmentalized system was first order, while that in the homogeneous solution was mixed first and second order. The second-order component is due to triplet-triplet annihilation. In homogeneous solution this annihilation leads to emission of delayed fluorescence. The compartmentalized systems also showed delayed fluoresence but with a lowered intensity as compared to the homogeneous systems with an equal amount of triplets formed. Compartmentalization does not shield the probe completely from triplet-triplet annihilation or other possible triplet deactivation paths. Triplet quenching by methyl viologen is diffusion controlled in homogeneous solutions but somewhat slower in -CD media. The rate of quenching of triplet RT by Cu(II) is less than diffusion controlled in noncompartmentalized systems. The rate constant of quenching is substantially lowered in the presence of the cyclodextrin. The reduction in quenching rate constant is attributed to compartmentalization in both cases. The quenching data indicate that the RT triplet is fully complexed by -CD.

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“…Studies in solution have revealed that the triplet lifetimes observed are sensitive to conformational changes induced by the environment or by substituents attached to various parts of the molecule. Incorporating these ketones into hosts such as cyclodextrins and zeolites significantly lengthens the triplet lifetime by hindering the movement of the β-phenyl ring. − The addition of methyl groups on either the β-position or on the β-phenyl ring itself can dramatically affect the triplet lifetime, depending on the number and location of the substituents . The effects of β-methyl substitution are attributed to restrictions in the rotation of the aryl ring away from the carbonyl which results in a more “locked” conformation and shorter triplet lifetime.…”

Section: Introductionmentioning

confidence: 99%

Time-Resolved Diffuse Reflectance Studies of β-Phenyl Ketones in the Solid State: Conformational and Chiral Control of Triplet Lifetimes

1996

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The triplet states of ketones having a β-aryl substituent, such as 2 and 3, decay in solution by a charge transfer interaction between this aryl group and the excited carbonyl. In the solid state, this interaction also provides an efficient mode of deactivation for 3, but not for 2, reflecting the proximity between the π-ring system in 3, but not in 2, where the molecules crystallize (X-ray) in a stretched conformation. In the case of 3, the triplet lifetime in the solid state is 420 ns for the pure R or S enantiomers, but 733 ns for the racemic crystals, showing an interesting case of chiral discrimination. Powder X-ray and solid state NMR data suggest that conformational and packing differences between the enantiomers and racemic crystals are responsible for differences in the efficiency of intramolecular deactivation.

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Effect of cyclodextrin complexation on the photochemistry of p-methoxy-β-phenylpropiophenone

Cited by 16 publications

References 11 publications

Dynamics of Probe Complexation to Bile Salt Aggregates

Dynamics of Probe Complexation to Bile Salt Aggregates

Bimolecular Processes of α-Terthiophene in a β-Cyclodextrin Environment: An Exploratory Study

Time-Resolved Diffuse Reflectance Studies of β-Phenyl Ketones in the Solid State: Conformational and Chiral Control of Triplet Lifetimes

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