For a molecule which contains an intr
amolecular hydrogen bond (IMHB) in its chemical structure to undergoan excited singlet intr
amolecular proton transfer (ESIPT) process, on photoexcitation, there must occur asimultaneous increase, in a substantial manner, in the acidity of the proton donor and the basicity of theproton acceptor forming the IMHB [
J. Am. Chem. Soc. 2001,
123, 11940]. For the reason that those changesoccur on photoexcitation of the 2-hydroxyacetophenone but not for 1-hydroxy-acetonaphthone, one drawsthe conclusion that, while ESIPT is operative in the 1(
,
*)
1 electronic state of the monocyclic compound2-hydroxyacetophenone, it is not operative in its bicyclic homolog 1-hydroxy-2-acetonaphthone. We haveshown the photophysics of 1-hydroxy-2-acetonaphthone in its first excited electronic state to be governed bytwo stable, easily reconverted enol structures, the presence of which causes the peaks in the free-jet fluorescenceexcitation spectrum for the compound to split into two of similar strength. In this paper, we rationalizephotophysical evidence for 1-hydroxy-2-acetonaphthone obtained by femtosecond spectroscopy over the past13 years in the light of existing photophysical patterns based on steady-state spectra for the compound [
J.Am. Chem. Soc.
1993,
115, 4321].