Viscosities of some organic glasses used as trapping matrixes

Ling, A. Campbell; Willard, John E.

doi:10.1021/j100855a053

Cited by 65 publications

(22 citation statements)

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“…This exception might be explained in terms of the local viscosity, which is possibly different from the bulk viscosity. Since the value of the viscosity for MCH was obtained by the extrapolation from viscosities of MCH-3MP mixtures to that of MCH (25), the true viscosity of MCH might be higher than that of 3MHx. Then, this case may not be an exception.…”

Section: Photobleaching Of Trapped Electrons (Ehc-) Inmentioning

confidence: 99%

Electron trapping in alcohol clusters in γ-irradiated n-propanol–hydrocarbon glasses at 77 K

Ito¹,

Kimura²,

Fueki³

1981

Can. J. Chem.

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MASAYA ITO, TOYOAKI KIMURA, and KENJI FUEKI. Can. J. Chem. 59, 2803 (1981). A study has been made of trapped electrons in n-propanol-hydrocarbon mixture glasses at 77 K by the optical absorption method. 1The yields of electrons trapped in alcohol clusters (e&) were measured for several y-irradiated n-propanol-hydrocarbon glasses, where the yields of trapped electrons in these neat hydrocarbon glasses at 77 K are known to range from 0.015 to 1.1 G units. The results show that the yields of e, . -in the mixture glasses do not depend on the trapped electron yields in neat hydrocarbon glasses. Thus, it is concluded that electron migration from relaxed hydrocarbon matrix traps into alcohol clusters is not the major process for eal,-formation in the systems studied here. The major process for eal,-formation may be attributed to quasi-free electron scavenging by alcohol clusters and electron migration from unrelaxed hydrocarbon traps into alcohol clusters. Both ir-induced and isothermal changes in the ea,-yield have also been investigated. These investigations indicate that there is a correlation between the observed change in the eal,-yield and the matrix viscosity.

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Section: Photobleaching Of Trapped Electrons (Ehc-) Inmentioning

confidence: 99%

Electron trapping in alcohol clusters in γ-irradiated n-propanol–hydrocarbon glasses at 77 K

Ito¹,

Kimura²,

Fueki³

1981

Can. J. Chem.

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“…For mini-3 the fluorescence was attributed to the 2 1 A g → 1 1 A g transition (41). In the temperature interval 133-77 K the viscosity of 3mp alters dramatically from less than 1 to 10 15 cP (44). Therefore, it is likely that the activation energy E a ϭ 540 cm Ϫ1 reflects a combination of a molecular potential barrier (E 0 ) and a viscosity-induced barrier (E), i.e.…”

Section: Photophysics Of Phytoene (N ‫؍‬ 3)mentioning

confidence: 99%

“…The quote k nr /k r is calculated from Eq. 4 and the viscosity () is taken from Ling and Willard(44)…”

mentioning

confidence: 99%

Photophysical Characterization of Natural cis-Carotenoids¶

Andersson¹,

Takaichi

Cogdell

et al. 2007

Photochemistry and Photobiology

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By means of steady-state fluorescence spectroscopy we explore the photophysics of two lowest lying singlet excited states in two natural 15-cis-carotenoids, namely phytoene and phytofluene, possessing three and five conjugated double bonds (N), respectively. The results are interpreted in relation to the photophysics of all-transcarotenoids with varying N. The fluorescence of phytofluene is more Stokes-shifted relative to that of phytoene, and is ascribed to the forbidden S 1 → S 0 transition, with its first excited singlet state (S 1 ) lying 3340 cm Ϫ1 below the dipole allowed second excited singlet state (S 2 ), at 77 K. For phytoene the S 2 and S 1 potential surfaces are closer in energy, probably giving rise to the mixed S 2 and S 1 fluorescence characteristics. The origin of phytoene fluorescence is discussed and is suggested to be due to the S 1 → S 0 transition; with the S 1 state located 1100 cm Ϫ1 below S 2 at 77 K. The dependence of the fluorescence quantum yield on temperature and viscosity shows that large amplitude molecular motions are involved in the radiationless relaxation process of phytoene. The transition dipole moment of absorption and emission are parallel in phytoene and nonparallel in phytofluene.

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“…This discrepancy may be due to differences in the process of internal conversion from SI and/or TI in both hydrocarbon solvents. MTHF at 77 K has an extrapolated viscosity of 10" poise, while a mixture of 80 per cent isopentane and 20 per cent methylcyclohexane would have a viscosity greater than the viscosity of isopentane at 77 K [lo1* P (Ling and Willard, 1968)], but much less than the viscosity of methylcyclohexane at 77 K [IO"P (Ling and Willard, 1968)l. In a less rigid solvent, we would expect that the probability of collisional deactivation of the excited singlet or triplet state would be greater in reducing the intersystem-crossing yield.…”

Section: Low -Field Spectrummentioning

confidence: 99%

An Epr Study of the Species Produced During the Uv Photolysis of Heterocyclic Compounds in Methyltetrahydrofuran at 77 K

Arce

Ramírez

1975

Photochem & Photobiology

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Abstract—The ultraviolet irradiation (290 nm ≤Λ≤ 390 nm) of indole, purine, indazole, acridine and quinoline in 2‐methyltetrahydrofuran glass at 77 K produces trapped radicals. Two electron‐paramagnetic‐resonance (EPR) signals are found at 77 K during illumination, one at high magnetic field (3–25 times 10‐1 T) assigned to the matrix radical and the other at low field (1.3 times 10‐1 to 1–5 times 10‐1 T) attributed to the lowest triplet state of the heterocyclic molecule. Quantum yields for triplet production at 77 K are 0–34 for indole, 0.51 for purine, 0.55 for indazole, 0.15 for acridine, and 0.94 for quinoline. The rate of formation of matrix radicals varies as the nRth power of the incident light intensity, I0nR, where 1.6 ≤nR=≤ 2. Solvent radical yields, which depend on the light intensity, have been determined. Under the experimental conditions, no signals attributable to trapped electrons or cations have been observed. The dependence of the reciprocal value of the rise lifetime of the low field EPR signal as a function of the intensity of exposure is in accordance with a biphotonic mechanism.

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Viscosities of some organic glasses used as trapping matrixes

Cited by 65 publications

References 1 publication

Electron trapping in alcohol clusters in γ-irradiated n-propanol–hydrocarbon glasses at 77 K

Electron trapping in alcohol clusters in γ-irradiated n-propanol–hydrocarbon glasses at 77 K

Photophysical Characterization of Natural cis-Carotenoids¶

An Epr Study of the Species Produced During the Uv Photolysis of Heterocyclic Compounds in Methyltetrahydrofuran at 77 K

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