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Tuning Excited-State Reactivity by Proton-Coupled Electron Transfer
1Center of Basic Molecular Science (CBMS), Department of Chemistry, Tsinghua University, Beijing, 100084, China.
Angewandte Chemie (International Ed. in English)
|September 17, 2016
Summary
Proton-coupled electron transfer (PCET) enhances excited state reactivity. Functionalized benzophenone (BP-COOH) exhibits superior oxidation power compared to simple benzophenone (BP) due to its intramolecular Brønsted acid.
Area of Science:
- Photochemistry
- Chemical Kinetics
- Organic Chemistry
Background:
- Excited state reactivity is crucial in chemical transformations.
- Proton-coupled electron transfer (PCET) offers a pathway to tune reaction dynamics.
- Benzophenone (BP) is a well-studied photosensitizer.
Purpose of the Study:
- To investigate the effect of an intramolecular Brønsted acid on the oxidation capability of excited benzophenone.
- To compare the reactivity of functionalized benzophenone (BP-COOH) with standard benzophenone (BP).
- To elucidate the mechanism behind enhanced electron removal from substrates.
Main Methods:
- Photochemical studies involving excited states of benzophenone derivatives.
- Kinetic measurements of electron transfer reactions.
- Spectroscopic analysis to understand reaction pathways.
Main Results:
- The triplet state of benzophenone functionalized with a Brønsted acid (3 *BP-COOH) demonstrated significantly enhanced oxidation capability.
- 3 *BP-COOH efficiently removed an electron from benzene at a rate of 8.0×105 m-1 s-1.
- The simple triplet state of benzophenone (3 *BP) was inactive towards benzene oxidation.
Conclusions:
- Intramolecular Brønsted acids can dramatically enhance the oxidative power of excited states.
- PCET, specifically concerted electron-proton transfer, is the key mechanism for this enhancement.
- This finding opens new avenues for controlling photochemical reactions through PCET modulation.
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