Solvent and substituent effect on intramolecular charge transfer in 5-arylidene-3-substituted-2,4-thiazolidinediones: Experimental and theoretical study

The substituent and solvent effect on intramolecular charge transfer (ICT) in 5-arylidene-3-methyl-2,4-thiazolidinediones (series 1) and 5-arylidene-3-phenyl-2,4-thiazolidinediones (series 2) was studied by using experimental and theoretical methodology. The effect of specific and non-specific solvent–solute interactions on the UV–vis absorption maxima shifts was evaluated by using the Kamlet-Taft and Catalán solvent parameter sets. Linear free energy relationships (LFERs) have been applied to the UV–vis and 13C NMR data by using SSP (single substituent parameter) and DSP (dual substituent parameters). Comparative LFER analysis of 10 styrenic series was performed in order to distinguish contribution of structural and electronic substituent effect on extent of π-polarization in a side chain (vinyl) group. Furthermore, the experimental findings were interpreted with the aid of ab initio MP2 and time-dependent density functional (TD-DFT) methods. TD-DFT calculations are performed to quantify the efficiency of intramolecular charge transfer (ICT) allowing us to define the charge-transfer distance (DCT), amount of transferred charge (QCT), and difference of dipole moments between the ground and excited states (μCT). It was found that both substituents and solvents influence electron density shift, i.e. extent of conjugation, and affect intramolecular charge transfer character in the course of excitation.