Synthesis, spectroscopic, theoretical and antimicrobial studies on molecular charge-transfer complex of 4-(2-thiazolylazo)resorcinol (TAR) with 3, 5-dinitrosalicylic acid, picric acid, and chloranilic acid

Charge-transfer complex of 4-(2-thiazolylazo) resorcinol (TAR) with 3, 5-dinitrosalicylic acid (3,5-DNSA), picric acid (PA), and chloranilic acid (CLA) were synthesized and characterized spectroscopically and investigated theoretically. Molecular composition of the prepared complexes was determined by mole ratio method. It was found that the stoichiometry of all prepared complexes is 1:2 (donor: acceptor) in methanol solvent. Stability constant of the prepared complexes were determined by using modified Benesi-Hildebrand equation. High values of formation constant of the complexes were signifying the high stability of the complexes. Different spectroscopic parameter as ionization potential (ID) of donor, oscillator strength (f), transition dipole moment (μEN), etc. were determined using UV–Vis spectroscopy in same solvent. The effect of solvent polarity on the charge-transfer spectra was also verified in four different solvents. The infrared spectrum studies of the solid complexes explore the presence of charge-transfer interaction through a hydrogen bonding interaction. TGA-DTA of the prepared complexes was also done to find out the thermal nature and stability of the complex. Synthesized complexes were checked for antibacterial and antifungal activities against different bacterial and fungal strains and complexes shows potent antibacterial and antifungal activity. DFT method was employed to view the molecular structure, electronic and spectroscopic nature of the studied complexes. MEP calculation, HOMO and LUMO energies, interaction energy, NBO analysis were performed on optimized structures of the complexes.