Peroxyoxalate High-Energy Intermediate is Efficiently Decomposed by the Catalyst Imidazole

Area of Science:

• Chemical Kinetics
• Chemiluminescence
• Photochemistry

Background:

• The peroxyoxalate reaction is a highly efficient chemiluminescence system.
• Chemiexcitation involves interaction between an activator (ACT) and a high-energy intermediate (HEI).
• Imidazole (IMI-H) catalyzes HEI formation and also decomposes it, but its rate constant is unknown.

Purpose of the Study:

• To determine the rate constant for the interaction between IMI-H and the HEI.
• To compare the efficiency of IMI-H with a classic ACT, 9,10-diphenylanthracene (DPA).
• To investigate the effect of IMI-H concentration on HEI decomposition and singlet excited state formation.

Main Methods:

• Kinetic measurements were employed to study the peroxyoxalate reaction.
• The decomposition of the HEI by IMI-H was analyzed.
• Singlet excited state formation quantum yield was determined at varying IMI-H concentrations.

Main Results:

• IMI-H is approximately four times more efficient than DPA in catalyzing HEI decomposition.
• A bimolecular electron transfer mechanism, similar to Chemically Initiated Electron Exchange Luminescence (CIEEL), is proposed for HEI decomposition by IMI-H.
• At equal concentrations, IMI-H consumes 78% of the generated HEI through nonemissive bimolecular interaction.
• The singlet excited state formation quantum yield at infinite ACT concentration was determined to be (5.5 ± 0.5) × 10⁻² E mol⁻¹.
• The yield of HEI formation was found to be independent of IMI-H concentration.

Conclusions:

• IMI-H is a highly efficient catalyst for HEI decomposition in peroxyoxalate chemiluminescence.
• The decomposition of HEI by IMI-H occurs via a bimolecular electron transfer process.
• The concentration of IMI-H does not influence the yield of HEI formation, suggesting a distinct pathway for its generation.