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Revisiting photoacidity using R*NH2 photoacids
H Rozler1, D Aminov1, D Pines1
1Department of Chemistry, Ben Gurion University of the Negev, Beer-Sheva 84105, Israel.
This study compares proton transfer reactions in R*NH2 and R*OH photoacids. Similar mechanisms were found, with differences attributed to solvent reorganization energy, impacting proton dissociation rates.
Area of Science:
- Photochemistry
- Chemical Kinetics
- Physical Chemistry
Background:
- Neutral photoacids, R*NH2 and R*OH, are crucial in understanding proton transfer dynamics.
- Proton transfer reactions are fundamental in various chemical and biological processes.
- Excited-state lifetimes significantly influence the observable proton transfer pathways.
Purpose of the Study:
- To compare time-resolved and steady-state proton transfer reactions in R*NH2 and R*OH photoacids.
- To analyze these reactions using free-energy correlations.
- To elucidate the role of solvent reorganization energy in observed differences.
Main Methods:
- Utilized time-resolved and steady-state fluorescence spectroscopies.
- Constructed free-energy correlations for R*NH2 photoacids with strong Brønsted bases.
- Compared these correlations with existing data for R*OH photoacids.
Main Results:
- Identified significant similarities in proton transfer mechanisms between R*NH2 and R*OH photoacids.
- Attributed differences in free-energy correlations to variations in local solvent reorganization energy.
- Demonstrated that R*NH2 photoacids are generally too weak to dissociate protons within their excited-state lifetime.
Conclusions:
- Proton transfer mechanisms in R*NH2 and R*OH photoacids share common features.
- Solvent effects, specifically reorganization energy, play a key role in modulating proton transfer.
- Free-energy correlations provide valuable insights into the kinetics and thermodynamics of photoacid proton transfer.
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