Excited-State Proton Transfer in Push-Pull N-Methyl Pyridium Reversible Super-Photoacids Ruled by Intramolecular Hydrogen-Bond-Like Interactions.

ABSTRACT: Three push-pull N-methyl pyridium phenols have been thoroughly investigated for their photoacid behavior through stationary and time-resolved spectroscopic techniques. Fluorimetric titrations revealed a clear excited-state proton transfer (ESPT) with negative pKa* values for the two molecules with the phenol attached in ortho relative to the double bond, so as to be regarded as super-photoacids. Conversely, no proton transfer was observed when the hydroxyl group was in the para position. Quantum-mechanical calculations confirmed that intramolecular hydrogen-bond-like interactions, only attainable in the ortho isomers, are strengthened by the charge transfer process occurring upon excitation, resulting in enhanced acidity. Ultrafast transient absorption and fluorescence up-conversion (UC) s

SUBMITTER: Cesaretti A 

PROVIDER: S-EPMC12712759 | biostudies-literature | 2025 Dec

REPOSITORIES: biostudies-literature