Solvatochromism of isatin based Schiff bases: An LSER and LFER study

Abstract

The derivatives of isatin (1H-indole-2,3-dione) have already been reported to show a variety of biological activities. However, there have hitherto been no reports on the solvatochromic effects of isatin derivatives, and it could be of interest to study and relate them to their electronic structures, as a part of the characterisation of these compounds. Linear solvation energy relationships (LSER) were used to analyze the influence of the solvent on the shifts of the UV absorption maxima of investigated isatin derivatives, i.e., isatin based Schiff bases, using Kamlet-Taft model. Linear free energy relationships (LFER) were applied to the substituent-induced NMR chemical shifts (SCS) using a single substituent parameter (SSP). The obtained correlations together with theoretical calculations gave insight into the influence of the molecular conformation on the transmission of substituent effects, as well as on solute-solvent interactions. The molecular electrostatic potential (MEP) surface map was plotted over the optimized geometry of the molecules in order to visualize the electron density distribution and explain the origin of the solvent-solute interactions.