GROUND- AND EXCITED-STATE PROTOTROPIC TAUTOMERISM IN ANILS OF AROMATIC α-HYDROXYALDEHYDES STUDIED BY ELECTRONIC ABSORPTION, FLUORESCENCE AND 1H AND 13C NMR SPECTROSCOPIES AND SEMI-EMPIRICAL CALCULATIONS

Article abstract of DOI:10.1002/poc.610081104

Proton transfer processes in both the ground and excited states in anils of aromatic α-hydroxyaldehydes (salicylaldehyde, 2-hydroxynaphthalene-1-carbaldehyde and the novel 10-hydroxyphenanthrene-9-carbaldehyde) have been studied by a combination of spectroscopic techniques.Solution 1H and 13C NMR is used to establish the position of the tautomeric equilibria.UV-visible absorption and fluorescence spectral data help to characterize the existence, in all cases, of excited-state intramolecular proton transfer (ESIPT) phenomena.Semi-empirical calculations involving full geometry optimization and calculation of heats of formation for the ground state (AM1) and vertical excitation energies and oscillator strengths (INDO/S) are in agreement with the experimental observations.