Premium
Quenching of Singlet Molecular Oxygen ( 1 O 2 ) by Azide Anion in Solvent Mixtures ¶
Author(s) -
Li M. Y.,
Cline C. S.,
Koker E. B.,
Carmichael H. H.,
Chignell C. F.,
Bilski P.
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0740760qosmoo2.0.co2
Subject(s) - chemistry , reaction rate constant , solvent , azide , aqueous solution , propylene carbonate , ethylene carbonate , photochemistry , quenching (fluorescence) , acetonitrile , solvent effects , singlet oxygen , inorganic chemistry , oxygen , organic chemistry , kinetics , fluorescence , physics , electrode , quantum mechanics , electrolyte , electrochemistry
The azide ion is a strong physical quencher of singlet molecular oxygen ( 1 O 2 ) and is frequently employed to show involvement of 1 O 2 in oxidation processes. Rate constants ( k q ) for the quenching of 1 O 2 by azide are routinely used as standards to calculate k q values for quenching by other substrates. We have measured k q for azide in solvent mixtures containing deuterium oxide (D 2 O), acetonitrile (MeCN), 1,4‐dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1 O 2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1 O 2 . In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. k q was 4.78 × 10 8 M −1 s −1 in D 2 O and increased to 26.7 × 10 8 and 27.7 × 10 8 M −1 s −1 in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D 2 O mixtures, k q decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol −1 in D 2 O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from k q values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown k q values.