INTRAMOLECULAR PROTON OR HYDROGEN-ATOM TRANSFER IN THE GROUND AND EXCITED-STATES OF 2-HYDROXYBENZOYL COMPOUNDS

Potential energy surfaces for the intramolecular proton transfer of gr ound (GSIPT) and excited (ESIPT) states of 2-hydroxybenzoyl compounds were obtained. Based on the results, intramolecular proton transfer in this type of compound is strongly dependent on the distances between the oxygen atoms that bear the intramolecular hydrogen bond (IMHB). Al so, the GSIPT curves for these compounds contain a single minimum that is located in the zone for the normal (enol) form. The ESIPT curves a lso contain a single minimum but lie in the zone for the keto form. Th ere is net correlation between the strength of the IMHB and the proton transfer barrier through it. The energy for the excited singlet 1(n,p i) for these compounds is strongly dependent on the resonance effect of the substituent, -R, so this state is the first excited singlet onl y in derivatives with nearly nonresonating R. The ESIPT processes are of the proton transfer type, even though the final form possesses no z witterionic connotations. Finally, these theoretical features are quit e consistent with photophysical experimental evidence for this type of compounds.