Disclosure of the solvatochromism and the reversal switch in some tailor-made electron push-push anils

Abstract

The impacts of a series of organic solvents, having diverse polarities on the electronic absorption spectra of some selected anils, N-benzylideneaniline, and its five derivatives with hydroxy and methoxy substituents were investigated. The absorption spectra of each of the anils displayed a cluster of absorption bands within 200–500 nm. The electronic transitions and the effect of substituents on the solvatochromism of these anils were successfully deciphered. The reversal in solvatochromism was observed in moving from the hydrogen bond acceptor to hydrogen bond donor solvents. This fact was attributed to the structural transition of the anils due to the interaction with solvents of differential polarity or due to the obscurity of anils within the solvent cage. The ET(30) values at which the reversal solvatochromic switch due to the anils appeared was controlled by the position and nature of the substituents. The early accomplishment of the reversal solvatochromism in o-OH substituted anils connoted the non-polar characteristics of these anils. By subjecting the electronic transition energies to multiple regression analysis with fourteen different solvent parameters, the multi-parametric regression models were optimized following the successive exclusion of variable technique. The linearity of the plot of the calculated electronic transition energy against corresponding observed values validated the regression models. The induced solvatochromism observed in the case of o/p-hydroxy-substituted anils in ethylene glycol medium was attributed to the formation of the corresponding conjugate acids of the anils. The solvent-solute interaction models were proposed to probe the localization site of anils in the solvents. The intramolecular H-bonding and the twisted structure of the anils due to the substituent effects were found to play the predominant role in deciding the localization sites of the anils.