High-performance Liquid Chromatographic Estimation of the π–π Charge-transfer Interaction Ability of Electron Acceptors Using Phenyl-silica Column

Abstract

The intermolecular π–π charge-transfer (CT) complex formation ability of electron acceptors, such as p-chloranil, tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, and 1,2,4,5-tetracyanobenzene, has been evaluated as retention factors of HPLC using a phenyl-silica column as a stationary phase with mobile phase consisting of heptane and benzene. It was found that there is a good linear correlation between the retention factors of the acceptors and the formation constants (K_CT) for the CT complexes with pyrene. On the other hand, half-wave reduction potentials (E_1/2) as experimental LUMO energies of acceptors are well correlated with the intermolecular CT band energies based on Mulliken’ CT theory, but unfavorably explain the K_CT values. Therefore, the retention factors obtained by the HPLC system are considered to be a direct indicator value of the intermolecular π–π type CT ability of electron acceptors. The proposed procedure could be useful as a simple method to know the intermolecular CT ability of acceptors instead of the electrochemical measurement of the E_1/2 values.