Acid-base reaction of a super‐photoacid with a cooperative amide hydrogen‐bonded chain

Abstract

The excited-state proton transfer (ESPT) of the strong photoacid, N-methyl-7-hydroxyquinolium (NM7HQ+), was studied in the presence of N-methylbenzamide (NMB) as a base in the aprotic polar solvent, acetonitrile. According to the Benesi–Hildebrand relation, it was revealed that the hydrogen (H)-bonded complex of NM7HQ+ and NMB exists in the ground state in a 1:1 stoichiometry with the association constant of 22.2 ± 1.7 M−1. The fluorescence quenching of the 1:1 complex was observed to follow the Stern–Volmer relation with the molecularity of one for NMB indicating that the ESPT of NM7HQ+ occurs with the H-bonded chain of two NMB molecules. Our study highlights the cooperative nature of H-bonding in the chemical reactivity of amide in acid–base reactions as has already been reported for alcohol.