Analysis of the association constants for charge-transfer complex formation

The phenomenon of charge transfer (CT) complex formation has been of interest for more than 50 years and has led to the development of numerous applications. Even with the prolonged interest in these complexes the interactions responsible for complex formation have yet to be fully characterized and remain an area of sustained relevance. This report outlines the measurement of the association constants for CT complex formation of a series of methylated benzene donors with tetracyanoethylene, pyromellitic dianhydride, 2,3-dichloro-5,6-dicyano-p-benzoquinone, and 1,2,4,5-tetracyanobenzene acceptors in 1,2-dichloroethane solvent. The evaluation of the position of the CT absorption maximum and the magnitudes of the association constants within a theoretical model is described. The influence of solvent polarity on the magnitudes of the association constants was also discussed. These studies show that non-bonding interactions are important in most complexes while ion-pair interactions play a significant role in a select few of the complexes studied.