Substituted benzylideneanilines: A family of solvatochromic probes

The solvatochromic behaviour of ten tailor-made structurally-related substituted N-benzylidineanilines was investigated in presence of solvents of varying polarities through inspection of UV-visible absorption spectra in the range 200 to 600 nm. The spectral bands were found to be significantly influenced by altering the polarity of the solvents. The o-hydroxy substituted N-benzylideneanilines were found to be less sensitive towards solvents in comparison to p-hydroxy substituted N-benzylideneanilines because of intramolecular hydrogen bonding between o-hydroxy group with the nitrogen atom of azomethine unit. The electronic transitions of these N-benzylideneanilines are observed to depend on specific as well as non-specific solute-solvent interactions arising out of the variation in nature and position of the substituent in the phenyl rings. The energy of interactions could very well discriminate the characteristics of solvents such as polar protic, polar aprotic and aprotic solvents. The solvatochromic behaviour and solvent-solute interactions were analyzed by means of well-studied multiparametric linear-solvation energy- relationship involving fourteen different solvent parameters. Optimization of multiparametric regression model was achieved by successive exclusion of variable technique. The validity of the regression model was established from the linearity of the plot of calculated and observed transition energy of the absorption. The overall studies divulge that the solvatochromism behaviour of the substituted N-benzylideneanilines under consideration could be exploited to classify solvents for desired applications.