Investigations on the chromatographic behavior of hybrid reversed-phase materials containing electron donor–acceptor systems: II. Contribution of π–π aromatic interactions

The chromatographic behavior of three naphthalimide-type stationary phases were elucidated in terms of hydrophobic, silanophilic and π–π interaction properties, employing besides common chromatographic column test methods from Engelhardt and Tanaka, also new test mixtures of geometrical and functional aromatic isomers. It was found that the presence of electron donor/acceptor moieties within a reversed phase system did not only increase the overall retention times for aromatic solutes, but also lead to an enhanced shape selectivity of the hybrid stationary phase. In this context, shape discrimination is primarily based on the number of accessible π-electrons for π–π interaction with the embedded electron deficient ligand moieties. The most outstanding results were obtained for the 1,4,5,8-naphthalenediimidic selector with its horizontal arrangement on the silica surface, which enables a direct face-to-face π–π interaction with aromatic solutes, with only little hydrophobic contribution.