Barrier-Lowering Effects of Baird Antiaromaticity in Photoinduced Proton-Coupled Electron Transfer (PCET) Reactions

Many popular organic chromophores that catalyze photoinduced proton-coupled electron transfer (PCET) reactions are aromatic in the ground state but become excited-state antiaromatic in the lowest ππ* state. We show that excited-state antiaromaticity makes electron transfer easier. Two representative...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2021-11, Vol.143 (43), p.17970-17974
Main Authors: Karas, Lucas J, Wu, Chia-Hua, Wu, Judy I
Format: Article
Language:English
Subjects:
Electrons
Light
Phenol - chemistry
Phenol - radiation effects
Photolysis
Pyridines - chemistry
Pyridines - radiation effects
Quantum Theory
Water - chemistry
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Summary:Many popular organic chromophores that catalyze photoinduced proton-coupled electron transfer (PCET) reactions are aromatic in the ground state but become excited-state antiaromatic in the lowest ππ* state. We show that excited-state antiaromaticity makes electron transfer easier. Two representative photoinduced electron transfer processes are investigated: (1) the photolysis of phenol and (2) solar water splitting of a pyridine–water complex. In the selected reactions, the directions of electron transfer are opposite, but the net result is proton transfer following the direction of electron transfer. Nucleus-independent chemical shifts (NICS), ionization energies, electron affinities, and PCET energy profiles of selected [4n] and [4n + 2] π-systems are presented, and important mechanistic implications are discussed.
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.1c09324