Excited-state acidity of bifunctional compounds Part 5 5-(2-Hydroxyphenyl)-3-phenyl-1,2,4-oxadiazole and 3-(2-hydroxyphenyl)-5-phenyl-1,2,4-oxadiazole

Abstract

Fluorescence emission and excitation spectra and experimental dipole moments are presented for 5-(2-hydroxyphenyl)-3-phenyl-1,2,4-oxadiazole and 3-(2-hydroxyphenyl)-5-phenyl-1,2,4-oxadiazole. These data indicate that the long-wavelength emission of the former, in non-hydrogen bonding solvents, is due to a tautomeric PT structure. The latter exhibits only the ‘normal’ band. The striking difference in behavior between these two compounds of very similar structure is explained on the basis of coplanarity between the aryl ring in position 5 and the heterocycle ring, the aryl ring in the 3 position not being in the same plane.