Open AccessWater-Triggered Photoinduced Electron Transfer in Acetonitrile–Water Binary Solvent. Solvent Microstructure-Tuned Reactivity of Hydrophobic Solutes
Author(s) -
Anna Lewandowska-Andrałojć,
Gordon L. Hug,
Bronisław Marciniak,
Gerald Hörner,
Dorota Światła-Wójcik
Publication year - 2020
Publication title -
the journal of physical chemistry. b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 392
eISSN - 1520-6106
pISSN - 1520-5207
DOI - 10.1021/acs.jpcb.0c02635
Subject(s) - ketyl , chemistry , flash photolysis , acetonitrile , solvent , quenching (fluorescence) , benzophenone , reaction rate constant , photochemistry , electron transfer , analytical chemistry (journal) , kinetics , organic chemistry , fluorescence , physics , quantum mechanics
The solvent-composition dependence of quenching triplet states of benzophenone ( 3 BP) by anisole in acetonitrile-water (ACN-H 2 O) mixtures was investigated by laser flash photolysis over the water mole fraction ( x w ) increasing from 0 to 0.92. Single exponential decay of 3 BP was observed over the whole composition range. The quenching rate constant consistently increased with the water content but increased far more rapidly with x w > 0.7. The water-triggered electron-transfer (ET) mechanism was confirmed by a steeply growing quantum yield of the benzophenone ketyl radical anion, escaping back-ET when the partial water volume exceeded the acetonitrile one. The water-content influence on the 3 BP quenching rate was described by a kinetic model accounting for the microheterogeneous structure of the ACN-H 2 O mixtures and the very different solubility of the reactants in the solvent components. According to the model, the ET mechanism occurs at a rate constant of 1.46 × 10 9 M -1 s -1 and is presumably assisted by the ACN-H 2 O hydrogen-bonding interaction.