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

Proton transfer processes in both the ground and excited states in anils of aromatic alpha-hydroxyaldehydes (salicylaldehyde, 2-hydroxynaphthalene-1-carbaldehyde and the novel 10-hydroxyphenanthrene-9-carbaldehyde) have been studied by a combination of spectroscopic techniques, Solution H-1 and C-13 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.