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

概要

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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 (KCT) for the CT complexes with pyrene. On the other hand, half-wave reduction potentials (E1/2) as experimental LUMO energies of acceptors are well correlated with the intermolecular CT band energies based on Mulliken' CT theory, but unfavorably explain the KCT 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 E1/2 values.