Competition between intra- and intermolecular proton transfer in the excited state of ortho-hydroxy derivatives of 2,5-diphenyl-1,3-oxazole in media of various acidity
Ao. Doroshenko et al., Competition between intra- and intermolecular proton transfer in the excited state of ortho-hydroxy derivatives of 2,5-diphenyl-1,3-oxazole in media of various acidity, RUSS J G CH, 70(4), 2000, pp. 573-578
The acid-base interactions of 2,5-diphenyl-1,3-oxazole and some model compo
unds in aqueous-alcoholic media were studied by electronic absorption and f
luorescent spectroscopy. The spectral-luminescent characteristics of the pr
ototropic forms were obtained, and the equilibrium constants of the protoly
tic processes were estimated. It was found that the presence of intramolecu
lr hydrogen bond only slightly affects the basicity of the ortho-hydroxy de
rivatives with respect to protonation by the oxazole ring in the ground sta
te. The elimination of the dimethylamino group from conjugation with the ma
jor chromophoric fragment of 2-(2-hydroxyphenyl)-5- [4-(dimethylamino)pheny
l]-1,3-oxazole by protonation of the former in a weakly acidic solution giv
es rise to fluorescence of the phototautomeric form, which is incharacteris
tic of this compound in a neutral medium.