Dynamics of Radical Pair Processes in Bulk Polymers

Chesta, Carlos A.; Weiss, Richard G.

doi:10.1002/9780470584118.ch13

Cited by 4 publications

(9 citation statements)

References 79 publications

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“…Decay kinetics of 3 B * measured at λ 630 nm obtained under laser flash photolysis of B in PS (a) and SEBS (b) films. Data in (a) were fitted to dispersive first order , and data shown in (b) were fitted to a combination of the first order and dispersive first order , as described in the text.…”

Section: Resultsmentioning

confidence: 99%

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Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

Levin

Efremkin

Sul’timova

et al. 2013

Photochem & Photobiology

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The kinetics of transients formed under photoexcitation of benzophenone (B) dissolved in three different polymers was studied by ns laser flash photolysis. These polymers were the soft rubbers poly (ethylene-co-butylene) (EB), polystyrene block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) and hard polystyrene (PS). We monitored the decay kinetics of triplet state (3)B(*) and of ketyl radicals BH(●). We observed exponential decay of (3)B(*) and two-stage decay kinetics of BH(●) in EB. The first stage is a fast cage recombination of a radical pair (BH(●), radical of polymer R(●)). The second slow stage of BH(●) decay follows the second-order law with a relatively high rate constant, which corresponds to recombination of BH(●) in a homogeneous liquid with a viscosity of only ~0.1 P (about five times of 2-propanol viscosity). Application of a magnetic field (MF) of 0.2 T leads to deceleration of both stages of BH(●) decay in EB by approximately 20%. Decay kinetics of both transients were observed in SEBS. There was no MF effect on BH(●) decay in SEBS. We only observed (3)B(*) in PS. Decay kinetics of (3)B(*) in this case were described as polychromatic dispersive first-order kinetics. We discuss the effects of polymer structure on transient kinetics and the MF effect.

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Section: Resultsmentioning

confidence: 99%

“…(19,20). fitted to dispersive first order (10), and data shown in (b) were fitted to a combination of the first order and dispersive first order (10), as described in the text.…”

Section: B In Sebs Filmmentioning

confidence: 99%

Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

Levin

Efremkin

Sul’timova

et al. 2013

Photochem & Photobiology

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“…Arrows indicate the onsets of the relaxation temperatures determined from emission spectra as described in Ref. . The error bars are based upon the differences between the average values for two separate runs on two different samples.…”

Section: Resultsmentioning

confidence: 99%

“…They were purified as described in Ref. and some of their physical properties of these polymers are collected in Table . Pyrene (PyH) (Aldrich, 99%) was recrystallized twice from ethanol.…”

Section: Methodsmentioning

confidence: 99%

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Modulation of the Photophysical Properties of Pyrene by the Microstructures of Five Poly(alkyl methacrylate)s Over a Broad Temperature Range

Atvars

Abraham

Hill

et al. 2013

Photochem & Photobiology

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Pyrene fluorescence spectra have been recorded in five poly(alkyl methacrylate)s (where alkyl is ethyl butyl, isobutyl, cyclohexyl and hexadecyl) over a 20-400 K temperature range. The changes in the position and the full width at half maximum (FWHM) of the 0-0 emission band (peak I) have been correlated with the structural characteristics of the alkyl groups in the different relaxation regimes of the polymers to assess the degree of coupling of the excited singlet states with the polymer cybotactic regions. Data treatment of the peak I positions using an electron-phonon model indicates that longitudinal optical modes are involved, and that the magnitude of coupling depends on the polymer structure and follows the same trend as the glass transition temperatures. The same spectral parameters have been correlated also with "hole" free volumes from positron annihilation spectroscopy over temperature ranges which span the glass or melting transitions of the polymers. Reasons why free volume and FWHM measurements follow the same trends, and other aspects of the systems, are discussed.

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Laser Flash Photolysis of Benzophenone in Polymer Films

Levin

Khudyakov²

2011

J. Phys. Chem. A

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With a nanosecond laser we studied flash photolysis of benzophenone (BP) dissolved in four different polymer films. We measured kinetics of decay of a triplet state of benzophenone (3)BP as well as kinetics of decay of benzophenone ketyl free radicals BPH(•). Polymer matrices have plenty of reactive C-H bonds, and the hydrogen abstraction by (3)BP leads to a formation of geminate pair which either recombines into molecular products or dissociates. Decay kinetics of (3)BP is well described by dispersive kinetics and in particular by the kinetic law suggested in Albery, W. J.; et al. J. Am. Chem. Soc. 1985, 107, 1854. We observed a broader distribution of rate constants in hard films. It was observed that the decay kinetics of transients radicals in the "hard" polymers is quite satisfactory described by the same law for dispersive kinetics. Kinetics of radicals decay in "soft" polymers is satisfactorily described as a diffusion-enhanced reaction. Effect of a hardness of polymer matrix on the measured kinetic parameters is discussed.

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Dynamics of Radical Pair Processes in Bulk Polymers

Cited by 4 publications

References 79 publications

Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

Decay Kinetics of Benzophenone Triplets and Corresponding Free Radicals in Soft and Rigid Polymers Studied by Laser Flash Photolysis

Modulation of the Photophysical Properties of Pyrene by the Microstructures of Five Poly(alkyl methacrylate)s Over a Broad Temperature Range

Laser Flash Photolysis of Benzophenone in Polymer Films

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