H-ATOM TRANSFER AND ROTATIONAL PROCESSES IN THE GROUND AND FIRST SINGLET EXCITED ELECTRONIC STATES OF 2-(2'-HYDROXYPHENYL)OXAZOLE DERIVATIVES - EXPERIMENTAL AND THEORETICAL-STUDIES
V. Guallar et al., H-ATOM TRANSFER AND ROTATIONAL PROCESSES IN THE GROUND AND FIRST SINGLET EXCITED ELECTRONIC STATES OF 2-(2'-HYDROXYPHENYL)OXAZOLE DERIVATIVES - EXPERIMENTAL AND THEORETICAL-STUDIES, Journal of physical chemistry, 100(51), 1996, pp. 19789-19794
The H-atom transfer and the rotational processes of 2-(2'-hydroxypheny
l)oxazole derivatives in both ground (S-0) and first singlet (S-1) exc
ited electronic states have been respectively studied from experimenta
l and theoretical points of view. Experiment and theory support the co
existence of two ground state rotamers, E and ER, with OH ... N and OH
... O hydrogen bonds, respectively, rotamer E being the most stable a
nd the only one that experiences a photoinduced H-atom motion in the S
-1 state. The fluorescence of 2-(2'hydroxyphenyl)-4-methyloxazole in a
rigid polymeric medium suggests that in fluid media the phototautomer
of the excited enol rotamer suffers a twisting motion around the C-C
bond linking both moieties of the molecule. Ab initio calculations at
the Hartree-Fock and CI-all-singles levels reveal (a) the existence of
a high-energy barrier to the H-atom transfer in the So state, whereas
in the S-1 state this transfer has a small or null energy barrier, (b
) a coupling between a charge transfer and the nuclear rearrangement (
OH and N ... O modes) that makes the system move from the enol to the
keto form, and (c) the presence of excited state rotamers of the keto
phototautomer in these oxazole derivatives.