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 ani ls of aromatic alpha-hydroxyaldehydes (salicylaldehyde, 2-hydroxynapht halene-1-carbaldehyde and the novel 10-hydroxyphenanthrene-9-carbaldeh yde) have been studied by a combination of spectroscopic techniques, S olution H-1 and C-13 NMR is used to establish the position of the taut omeric equilibria. UV-visible absorption and fluorescence spectral dat a help to characterize the existence, in all cases, of excited-state i ntramolecular proton transfer (ESIPT) phenomena, Semi-empirical calcul ations involving full geometry optimization and calculation of heats o f formation for the ground state (AM1) and vertical excitation energie s and oscillator strengths (INDO/S) are in agreement with the experime ntal observations.