Charge-transfer complexes. Part XII. Viscosity dependence of the intensity of contact charge-transfer absorption bands

Abstract

As the viscosity of the solvent is increased by addition of ethylene glycol to ethanol, the intensity of the contact charge-transfer absorption bands of the oxygen complexes of benzene and NN-dimethylaniline diminishes, tending towards zero in highly viscous media. This contrasts with the behaviour of the π-molecular complex, chloranil–hexamethylbenzene, which has the intensity of its charge-transfer band essentially independent of viscosity. These results are in accord with the model for contact complexes in which the light absorption to the charge-transfer state occurs during random collisions between the components.