Comprehensive computational studies of the effect of solvents relative permittivity on molecularity of direct azo dyes

Abstract

The present study concerns with the computational and experimental studies of Azo based direct dyes under the effect of solvents with different relative permittivities. Spectroscopic and structural analysis of the dyes was studied with density functional theory method (DFT) method at B3LYP level with 6-31G+/6-311G++ basis set. Computational calculations of geometric parameters (bond orders, bond lengths, and dihedral angles), electron densities, thermodynamic parameters and orbital energies were carried out for the dye compounds. Comparative study of computed infrared (IR) spectra with good agreement to experimental (FTIR) spectrum were shown for vibrational analysis for the dye compounds at B3LYP/6-311G++ level in gas phase and in different solvents. Potential energy distribution (PED) was employed to assign the different modes of vibrations. The computed IR and Raman spectra also showed appreciable agreement with the experimental recorded one. To check solvents effect, mulliken population analysis (MPA) and natural population analysis (NPA) were also performed at B3LYP level within the gas and different solvents (water, DMSO, acetonitrile, methanol and heptane). In gas and various solvents such as water, DMSO, ethanol and acetonitrile the electronic absorption spectra of the compounds have been computed employing DFT/ B3LYP with 6-311G++ basis set that showed very close agreement with the experimental spectra. For understanding the intramolecular and intermolecular bonding of the compound, NBO analysis was carried out and the density transfer from completely filled to unfilled orbital was found. Molecular electrostatic potential (MESP) calculations were performed for predicting the reactivity of dyes compound. The mechanism of intramolecular charge transfer was analyzed by determining the HOMO-LUMO energies and energy gaps. The degradation mechanism for one of the azo dye named DPABSA through OH radical attack was investigated with DFT/6-31G(d)/B3LYP Model. Keywords: Azo Dye; DFT; NPA; HOMO-LUMO; NBO; Absorption; Degradation; PED.