Molecular spectroscopic studies of charge transfer complexes of thiourea derivatives with benzoquinones

Charge transfer complexes of substituted-N-aryl-N-4-(-p-anisyl-5-arylazothiazolyl)thiourea with 2,3-dichloro-5,6-dicyanobenzoquinones (DDQ), chloranilic acid (CHLA), chloranil (CHL), bromanil (BRL) and iodanil (IDL) in methylene chloride were investigated spectrophotometrically to determine association constants (K), molar extinction coefficients (epsilon) and stoichiometric ratio. The effect of thermodynamic parameters (Delta G* and Delta H) on the stability of the complexes are discussed and the transition energy (E) of the CT complexes are reported. The solid CT complexes of the substituted-N-aryl-N-4-(-p-anisyl-5-arylazothiazolyl)thiourea with the above acceptors have been prepared and investigated by IR, electronic, H-1 NMR and ESR spectroscopy. Nonacidic acceptors yield complexes having pi-pi* and n-pi* bonding. Acidic acceptors yield complexes having pi-pi* and proton transfer interaction. The formation of 1:2 (D:A) complexes is also ascertained. (C) 2005 Elsevier B.V. All rights reserved.