Solvatochromism in N-(2-hydroxybenzylidene)aniline, N-(2-hydroxybenzylidene)benzylamine, and N-(2-hydroxybenzylidene)-2-phenylethylamine

Solvatochromism is found stronger in N-(2-hydroxybenzylidene)benzylamine (II) and N-(2-hydroxybenzylidene)-2-phenylethylamine (III) than in N-(2-hydroxybenzylidene)aniline (I) because of the increased basicity of the imine nitrogen in the ground state. Electronic absorption and FT-IR spectroscopic studies have provided evidence for an enol-keto tautomerism in all three compounds investigated in methanol, while both keto and protonated tautomers have been observed in their solutions in 2,2,2-trifluoroethanol and in 1,1,1,3,3,3-hexafluoro-2-propanol. The increase of the C=N stretching frequency upon protonation is found to be 21-18 cm(-1) in the compounds investigated in acidic solvents. The higher frequency of the quadrant doublet in the FT-IR spectrum of I is associated with the aromatic stretching vibrations of the aniline ring.