Spectrophotometric-chemometrics study of the effect of solvent composition and temperature on the spectral shape and shift of copper and nickel phthalocyanines in different aqueous-nonaqueous mixed solvents.

Abstract

Phthalocyanines (Pcs) are green-blue colored aromatic macrocyclic compounds used extensively in the dyeing industry. The assembly phenomenon for dye molecules is directly traceable by most of the spectroscopic methods. In this investigation, the monomer-dimer equilibria of copper and nickel phthalocyanines tetra sulfonic acid tetrasodium salts (CuPcTS, NiPcTS) have been investigated by spectrophotometric and chemometrics methods in binary mixtures of H2O-DMSO and H2O-CH3CN. The dimerization constants, (KD), enthalpies and entropies of CuPcTS and NiPcTS have been calculated by studying the UV-Vis spectra at different concentrations of dyes (10-6 to 10-4molL) and in the temperature range 298-343 K and in some samples up to 353 K by multivariate curve resolution (mcr) methods. By increasing the temperature, the value ofKD decreases. The inverse temperature dependence of KD(van't Hoff equation) was used for determination of ΔH0 and ΔS0and following that ΔG0of the dimerization reactions. As a result, upon aggregation, an increase in the intensity of the new shoulder at (~600 nm) and the Q-band at (662-670 nm) and concomitant decrease of the dimer band at (630-624 nm) are observed for all of the samples in different solvents composition. Therefore, the H-dimer type of these pigments was notable, in studied binary solvents. The effect of the solvent composition, concentration dye, and temperature on the spectral responses, the exciton parameters and concentration distribution diagrams of the two pigments were studied and discussed. The density functional theory (DFT) calculations were done in the aqueous and gas phase that they were included the HOMO-LUMO energies and the simulated UV-Vis spectrum. These calculations were beneficial for studying the UV-Vis spectrum of it in the aqueous phase for checking experimental data.