Use of a Zwitterionic Isoquinolinium Dye as a Solvatochromic Indicator: Structure of the Microsphere of Solvation and Explicit Solvation Modeling.

The present study uses a hybrid approach to investigate the negative solvatochromism and preferential solvation of iso-quinolinium dicarboethoxy methylid (iQ) in pure and binary solvent mixtures. UV-vis absorbance studies were combined with DFT and TD-DFT methods with implicit and explicit solvation models. The binary solvent mixtures, formed from inert and protic polar solvent pairs, were treated within the Bosch-Rosés preferential solvation models. The solvatochromic analysis revealed that the behavior in binary mixtures is described by the general model, suggesting that the two solvents interact and the electrostatic forces are involved. Application of the statistical cell model confirms that the composition of the microsolvation sphere of iQ in binary mixtures consists mainly of the protic solvent. The DFT study in the implicit solvation model reproduced the excitation energies of iQ reasonably well. Explicit solvation studies using benzene and water revealed the stabilization of iQ in the inert solvent, the preferred interaction sites of water with iQ, and the effect of the location of explicit solvent molecules on the calculated absorption spectra.