Abstract:The reactions of poly(4-vinylbiphenylj (denoted as PVB) polymers and biphenyl molecules with solvated electrons in the 2-methyltetrahydrofuran(MTHFj solvent have been studied at 100-120 K by electron-pulse radiolysis. The formation of PVB polymer anions as well as biphenyl anions was observed by the electron-pulse irradiation of the MTHF-PVB(or biphenyl) solution. The anions are formed by two processes; a rapid formation during the pulse irradiation (<20 ns) and a slow formation after the pulse irradiation. Th… Show more
“…The complex kinetics of such reactions are not only relevant for the particular problem that is addressed in this work but are of general importance . Examples of diffusion-limited reactions of the type discussed here include fluorescence quenching, , reaction of small reactive species with polymers, and the binding of a small substrate to the catalytic site of an enzyme − and numerical methods. − 1 Molecular structure of MEH−PPV. …”
In this paper, we describe how we derive the mobility of positive charges (“holes”) along isolated conjugated
polymer chains from the results of pulse-radiolysis time-resolved microwave conductivity (PR-TRMC)
experiments on dilute polymer solutions. The method is illustrated with results for oxygen-saturated, benzene
solutions of the well-known poly(phenylene vinylene) derivative, MEH−PPV with an average chain length
of 800 monomer units. Nanosecond pulsed irradiation results initially in ionization of the solvent with the
formation of excess electrons and benzene radical cations, Bz+. The former rapidly (<1 ns) undergo attachment
to O2 to form O2
- with a rate constant of 1.5 × 1011 M-1 s-1. The Bz+ ions diffuse through the solvent and
react with the (lower ionization potential) polymer chains via electron abstraction forming holes on the polymer
backbone. This is accompanied by a large increase in the conductivity of the solution after the pulse,
demonstrating that the mobility of holes on the polymer chains is very much larger than the mobility, via
molecular diffusion, of Bz+ ions in the solvent. To describe the after-pulse growth in conductivity, a large
effective reaction radius, R
eff, of ca. 400 Å is required for the diffusion-controlled reaction of Bz+ with MEH−PPV chains. This requires taking into account the time-dependent term in the rate coefficient. The value of
R
eff is compared with theoretical predictions for the reaction of a small entity with a 1-D linear or a 3-D cubic
array of 800 reactive moieties. The conclusion that individual polymer chains in solution must have a very
open structure with a large persistence length is in agreement with the results of previous static and dynamic
light-scattering studies. The conductivity eventually decays because of the recombination of the positively
charged polymer chains with negative counterions (O2
-) with a rate coefficient of 1.2 × 1011 M-1 s-1, which
is somewhat slower than predicted by the Debije equation. No evidence could be found for first-order trapping
of the mobile positive charge on the polymer chains prior to recombination. The pseudo-one-dimensional
mobility of holes along the polymer backbone derived from the absolute magnitude of the conductivity transients
is 0.46 cm2 V-1 s-1.
“…The complex kinetics of such reactions are not only relevant for the particular problem that is addressed in this work but are of general importance . Examples of diffusion-limited reactions of the type discussed here include fluorescence quenching, , reaction of small reactive species with polymers, and the binding of a small substrate to the catalytic site of an enzyme − and numerical methods. − 1 Molecular structure of MEH−PPV. …”
In this paper, we describe how we derive the mobility of positive charges (“holes”) along isolated conjugated
polymer chains from the results of pulse-radiolysis time-resolved microwave conductivity (PR-TRMC)
experiments on dilute polymer solutions. The method is illustrated with results for oxygen-saturated, benzene
solutions of the well-known poly(phenylene vinylene) derivative, MEH−PPV with an average chain length
of 800 monomer units. Nanosecond pulsed irradiation results initially in ionization of the solvent with the
formation of excess electrons and benzene radical cations, Bz+. The former rapidly (<1 ns) undergo attachment
to O2 to form O2
- with a rate constant of 1.5 × 1011 M-1 s-1. The Bz+ ions diffuse through the solvent and
react with the (lower ionization potential) polymer chains via electron abstraction forming holes on the polymer
backbone. This is accompanied by a large increase in the conductivity of the solution after the pulse,
demonstrating that the mobility of holes on the polymer chains is very much larger than the mobility, via
molecular diffusion, of Bz+ ions in the solvent. To describe the after-pulse growth in conductivity, a large
effective reaction radius, R
eff, of ca. 400 Å is required for the diffusion-controlled reaction of Bz+ with MEH−PPV chains. This requires taking into account the time-dependent term in the rate coefficient. The value of
R
eff is compared with theoretical predictions for the reaction of a small entity with a 1-D linear or a 3-D cubic
array of 800 reactive moieties. The conclusion that individual polymer chains in solution must have a very
open structure with a large persistence length is in agreement with the results of previous static and dynamic
light-scattering studies. The conductivity eventually decays because of the recombination of the positively
charged polymer chains with negative counterions (O2
-) with a rate coefficient of 1.2 × 1011 M-1 s-1, which
is somewhat slower than predicted by the Debije equation. No evidence could be found for first-order trapping
of the mobile positive charge on the polymer chains prior to recombination. The pseudo-one-dimensional
mobility of holes along the polymer backbone derived from the absolute magnitude of the conductivity transients
is 0.46 cm2 V-1 s-1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
