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

Citation
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
Citations number
47
Categorie Soggetti
Chemistry Physical
ISSN journal
00223654
Volume
100
Issue
51
Year of publication
1996
Pages
19789 - 19794
Database
ISI
SICI code
0022-3654(1996)100:51<19789:HTARPI>2.0.ZU;2-C
Abstract
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.