General Method for Determining Redox Potentials without Electrolyte
- Brookhaven National Lab. (BNL), Upton, NY (United States). Dept. of Chemistry
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Kyoto Inst. of Technology (Japan)
A novel method to determine redox potentials without electrolyte is presented here. The method is based on a new ability to determine the dissociation constant, $$K°_d$$, for ion pairs formed between any radical anion and any inert electrolyte counterion. These dissociation constants can be used to determine relative shifts of redox potential as a function of electrolyte concentration, connecting referenced potentials determined with electrochemistry (with 0.1 M electrolyte) to electrolyte-free values. Pulse radiolysis created radical anions enabling determination of equilibrium constants for electron transfer between anions of donor and acceptor molecules as a function of electrolyte concentration in THF. The measurements determined “composite equilibrium constants”, $$K_{eqC}$$, which contain information about the dissociation constant for the electrolyte cations, X+, with the radical anions of both the donor, $$K°_d$$(D–•,X+) and the acceptor, $$K°_d$$(A–•,X+). Dissociation constants were obtained for a selection of radical anions with tetrabutylammonium (TBA+). The electrolyte was found to shift the reduction potentials of small molecules 1-methylpyrene and trans-stilbene by close to +130 mV whereas oligo-fluorenes and polyfluorenes experienced shifts of only (+25 ± 6) mV due to charge delocalization weakening the ion pair. These shifts for reduction of aromatic hydrocarbon molecules are smaller than shifts of +232 and +451 mV seen previously for benzophenone radical anion with TBA+ and Na+ respectively where the charge on the radical anion is localized largely on one C=O bond, thus forming a more tightly bound ion pair.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- SC0012704
- OSTI ID:
- 1632388
- Report Number(s):
- BNL--215993-2020-JAAM
- Journal Information:
- Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory Journal Issue: 26 Vol. 124; ISSN 1089-5639
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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