Measurement of the Relative Mobility of Geminate Ions in Ethereal Solutions of Aromatic Compounds Using the Fluorescence Response of the Solutions to Pulsed Irradiation

Abstract

This work examines the possibility of using the fluorescence response of irradiated solutions of luminophores and the effect of an external electric field on the fluorescence decay to determine the mobility of geminate radical ions when using aliphatic ethers as the solvents. As an example, p-terphenyl solutions were studied in a series of ethers (diethyl, dibutyl, methyl tert-butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, eucalyptol, and 1,2-dimethoxyethane). Verification of the nature of the charge carriers in the irradiated solutions was made by means of the method of the time-resolved magnetic field effect in recombination fluorescence of spin-correlated radical ion pairs. It was found that at a p-terphenyl concentration of about 10 mM, the observed fluorescent response from the solutions, in most cases, was due to the recombination of radical ions formed from the aromatic solute. The relative mobility of p-terphenyl radical ions in ethers was estimated by using a stochastic computer simulation of the radiation spur composed of 4 primary ion pairs. The ions' mobility was found to be dependent on solvent viscosity in accordance with Walden's rule, with no noticeable effect of solvent polarity.

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

“…This characteristic time τ and the mobility relate as μ ≈ 1.1•4k B T/(eEτ), where k B T is the Boltzmann energy, e is electron charge and the multiplier 1.1 is a correction factor as determined by computer simulation. 70,71 Ratios presented in Figure 4b can be more or less accurately characterized with a single decay time, but the dependence of this time on an electric field differs somewhat from the quadratic one. This can probably be assigned to a dependence of charge carrier mobility on the electric field strength in PE.…”

“…Such a long-time quenching is similar to that previously observed in liquid solutions. 63,70,71 According to those studies, if radiation-induced fluorescence is determined by the recombination of ions, the mobilities of which are independent of electric field and time, then I E (t)/ I 0 (t) ratios can be described by exponents with a characteristic decay time that is almost independent of the primary track structure and is inversely proportional to the square of the electric field strength, E 2 , and to the sum of mobilities of the geminate ions, μ. This characteristic time τ and the mobility relate as μ ≈ 1.1•4k B T/(eEτ), where k B T is the Boltzmann energy, e is electron charge and the multiplier 1.1 is a correction factor as determined by computer simulation.…”

Probing an Isolated Conjugated Polymer Molecule with Radiation-Generated Spin-Correlated Polaron Pairs

“…The modeling was performed assuming that starting from the beginning, spin dynamics of the spin-correlated pair is solely determined by radical ions, whose EPR spectra are Gaussian in shape with widths of ΔB pp = 0.72 mT for the radical cations and ΔB pp = 0.66 mT for the radical anions. The used values are the same as those previously obtained for the p- TP- h 14 radical ions in liquid solution . This result implies comparatively rapid large-amplitude librations or rotation of the radical ions in the PVC matrix under the experimental conditions.…”

“…The used values are the same as those previously obtained for the p-TP-h 14 radical ions in liquid solution. 20 This result implies comparatively rapid large-amplitude librations or rotation of the radical ions in the PVC matrix under the experimental conditions. Note that the EPR spectra of secondary radical ions of aromatic compounds observed 21 in a polyethylene matrix also did not exhibit noticeable anisotropic broadening.…”

Sub-picosecond Production of Solute Radical Cations in Tetrahydrofuran after Radiolysis

“…In work examining ultrafast electron capture by conjugated polymers in THF, we noted possible production of polymer radical cations faster than 15 ps, but were unable to identify the source . Finally there have been a number of reports of delayed emission and triplets in ethers including THF − as well as in methanol and ethanol. , These are puzzling results as one would normally expect such chemistry only follows recombination of radical anions and radical cations, which should not exist in rapidly hole-fragmenting media.…”