Spectroscopic studies of charge-transfer complexes of 2,3-dichloro-5,6-dicyano-p-benzo-quinone with p-nitroaniline

The charge-transfer complexes of the donor p-nitroaniline (PNA) with the acceptor 2, 3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), were studied spectrophotometrically in various solvents such as CH2Cl2, CHCl3, and CCl4 at different temperatures. Two charge-transfer bands were observed in each case. The results, indicate that the formation of the CT-complex in a less polar solvent is comparatively high. The stoichiometry of the CT-complex was found to be 1:1. The physical parameters of the CT-complex were evaluated by the Benesi-Hildebrand equation. The data are discussed in terms of the formation constant (K-CT), molar extinction coefficient (epsilon(CT)), standard free energy (Delta G degrees), oscillator strength (f), transition dipole moment (mu(EN)), resonance energy (R-N) and ionization potential (I-D). The results indicate that the formation constant (K-CT) for the complex is dependent upon the nature of electron acceptor, donor and polarity of solvents used. The formation of the complex was confirmed by UV-visible, FT-IR, and H-1-NMR techniques. The possible structure of the CT-complex between DDQ and PNA was proposed.