Quantum chain processes. Novel procedure for measurment of quenching parameters. Evidence that exothermic triplet-triplet energy transfer is not diffusion limited and an estimation of the efficiency of exothermic quenching in a solvent cage

Turro, Nicholas J.; Schore, Neil E.; Steinmetzer, Hans‐Christian; Yekta, Ahmad

doi:10.1021/ja00813a050

Cited by 18 publications

(10 citation statements)

References 3 publications

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“…On the other hand, Wagner and Kochevar suggested that energy transfer competes with diffusion apart of the encounter pairs in the quenching of the triplet state of valerophenone by 2,5,-dimethyl-2,4-hexadiene by the stationary-state measurements . The same conclusion was reported on the basis of the evidence obtained from the quenching of thermally produced acetone triplets by acceptors . Subsequently, the rate constants for the quenching of singlet and triplet states of aromatic molecules by a series of azo compounds with varying steric properties were measured, and the significance of the contribution of steric hindrance to these collisional exothermic energy transfer processes was pointed out .…”

Section: Introductionmentioning

confidence: 64%

Exothermic Triplet−Triplet Excitation Transfer in Solution under High Pressure

Okamoto¹

1998

J. Phys. Chem. A

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The rate constants, k q, for the exothermic energy transfer from the triplet states of benzophenone (3BZP*) and triphenylene (3TPh*) to naphthalene (N), and also from the singlet sate of triphenylene (1TPh*) to benzophenone (BZP), were measured in polar and nonpolar solvents as a function of pressure at 25 °C. For all the systems of the donor−acceptor pairs, the plots of k q against 1/η showed downward curvature. For 3BZP*/N in acetonitrile, methanol, and n-hexane, the plots of ln k q against ln η were linear with the slopes larger than −1, while for 3BZP*/N in toluene and for 1TPh*/BZP in n-hexane they showed downward curvature. However, the plots of 1/k q against η were linear with positive intercepts for all the systems examined. It was also found that the plot of 1/k q against η/T, in which k q was measured for 3BZP*/N as a function of temperature and pressure in n-hexane, is linear. These results were interpreted by the energy transfer mechanism via the formation of an encounter complex between the donor and acceptor molecules, and it was concluded that the exothermic energy transfer examined in the present study is not fully diffusion-controlled but competes with a diffusion process that is expressed by a modified Debye equation. The bimolecular rate constants for the energy transfer, k bim (=k diff k et/k - diff), were in the range of (1−10) × 1010 M-1 s-1 depending on solvent. The pressure dependence of k et is discussed from the experimental fact that k bim is independent of solvent viscosity changed by varying pressure and temperature in all the systems examined.

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Section: Introductionmentioning

confidence: 64%

Exothermic Triplet−Triplet Excitation Transfer in Solution under High Pressure

Okamoto¹

1998

J. Phys. Chem. A

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“…That they do not may be seen in Figure 1, where it would seem that there are several intermediates involved in the photosensitized rearrangement of ira«5-crotyl chloride (1-t) to 1-c, 2, and 3-c and 3-t, with the latter two giving rise to the same line and thus presumably arising from the same intermediate. A very simple mechanistic scheme for a triplet-sensitized reaction is given (Scheme I) in eq [5][6][7][8][9][10][11] involving sensitizer S, reactant R, and quencher Q to give a particular product P, where the superscript refers to excited-state multiplicity and 3R-S indicates an excited-state complex.…”

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confidence: 99%

“…ÍRd 3R (or 3R-S) -*-°R + other products, if any (10) /CRQ 3R (or 3R-S) + Q -> °R + other products, if any, + Q (11) With the assumptions of eq 5-11, eq 12 may be readily q \L &SrIRJ + ^Sd.…”

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confidence: 99%

Photochemical transformations. 20. Intermediates in the sensitized photorearrangements of the .alpha.- and .gamma.-methylallyl chlorides

Cristol¹,

Micheli²

1978

J. Am. Chem. Soc.

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The acetone-sensitized photorearrangements of a-and cisand trans-7-methylallyl chlorides to each other and to cisand írarw-2-chloro-l-methylcyclopropane have been studied. Quenching with piperylene of the cyclopropyl chloride formation indicates that excitation transfer from triplet acetone to the allylic chlorides occurs at a rate approximately 1/100 that of transfer to piperylene, and gives a species with a quenchable lifetime of 2-3 ns which leads to the rearrangement-cyclization. Quenching of the triplet-sensitized rearrangements of Zra/ir-crotyl chloride to the cis isomer and to the allylic isomer gives similar excitation transfer rate constants with a quenchable lifetime of about 10 ns for the cis isomer production, and with a negative "lifetime" for the a isomer formation. These results are not consistent with the idea that a single quenchable intermediate leads to all of the products. The data are consistent with the idea that there are two (or more) excited-state intermediates, one of which (differing from each allylic isomer) leads to the cyclopropanes. The second intermediate may be postulated to interconnect the three allylic isomers, with its decay ratio in the absence of quencher different from its decay ratio when it interacts with quencher.The a-methylallyl chloride-7-methylallyl (crotyl) chloride system was the first one in which the photosensitized rearrangement of allylic halides to cyclopropyl halides was observed.2 The general reaction (eq 1) may be described formally as a [l,2]-sigmatropic rearrangement, accompanied (or followed) by ring closure, similar to the di-rr-methane rear-

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“…Not to be overlooked is a 1966 paper by Fry, Liu, and Hammond reporting that ferrocene quenches anthracene triplets in benzene solution at the diffusion-controlled rate.29 Provided this quenching occurs exclusively by energy transfer, this result should be interpreted to mean that the ferrocene triplet lies below the anthracene triplet (43 kcal/ mol) in energy. Although others have suggested alternative quenching mechanisms for ferrocene, Fry, Liu, and Hammond found no evidence that they apply.…”

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confidence: 99%