Charge transfer complexes of paraquat with drugs

Molecular complexes of paraquat (PQ) with a few drug intermediates in alkaline medium, viz. 2,4,6-trimethylphenol, 4-benzyloxyphenol, 2-cyanophenol, 4-cyanophenol and a few drugs, viz. diclofenac sodium, salmeterol, omeprazole, esomeprazole and pantoprazole in methanol have been studied spectrophotometrically. All the complexes exhibit one charge transfer band each in the region where neither of the components have any absorption. The stoichiomtry of each complex is found to be 1:1 from Job’s method. The ionization potentials of the donors (drugs) have been determined from the position of CT band of PQ – drug complex. The stability constants of the complexes have been determined from Rose-Drago method. Extinction coefficients (ε), oscillatory strengths (f) and transition dipole moments (D) of CT complexes have also been determined. For a given complex the extinction coefficients, the oscillatory strengths and the dipole moments are found to be almost independent of temperature. The constancy of ε, f and D over the temperature range studied rules out the possibility of existence of the complexes other than 1:1 stoichiometry.