Opposite Substituent Effects in the Ground and Excited States on the Acidity of N-H Fragments Involved in Proton Transfer Reaction in Aromatic Urea Compounds

Overview

Journal Photochem Photobiol Sci

Publisher Springer

Specialties Biology
Chemistry

Date 2021 Mar 27

PMID 33772478

Citations 1

Authors

Kei Togasaki

Tatsuo Arai

Yoshinobu Nishimura

Affiliations

Soon will be listed here.

Abstract

To investigate substitution effects on excited-state intermolecular proton transfer (ESPT) reactions as well as acidity of proton donating fragments in the ground state, we synthesized substituted anthracen-2-yl-3-phenylurea derivatives that form a hydrogen bonds with acetate anions and undergo ESPT reaction. Fluorescence lifetime measurements and their kinetic analyses revealed that the trifluoromethyl group on the phenyl ring as an electron-withdrawing group caused a slow ESPT reaction despite an increase in the acidity of the N-H fragment in the ground state. In contrast, the methoxy group as a donating group leads to a fast ESPT reaction despite a reduction of the acidity of the N-H fragment in the ground state. These effects of substituents on ESPT reaction are due to their influence on the charge transfer reaction, which occurs from the N-H fragment to the anthryl ring to increase the acidity of N-H followed by ESPT reaction, over the urea unit by a combination of resonance and inductive effects. These opposing effects of substituents on the acidity of the urea unit in the ground and excited states provide an important insight in balancing the reactivity of proton transfer reaction in both the excited and ground states.

Citing Articles

Substituent effects of halogens on the excited-state intermolecular proton transfer reactions.

Oyama H, Nishimura Y Photochem Photobiol Sci. 2024; 23(7):1341-1352.

PMID: 38850493 DOI: 10.1007/s43630-024-00598-3.

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