Tuning selectivity via electronic interaction: Preparation and systematic evaluation of serial polar-embedded aryl stationary phases bearing large polycyclic aromatic hydrocarbons

Abstract

Aromatic stationary phases showing complementary selectivity to their alkyl counterparts are extremely useful for certain challenging separation tasks. Herein, a series of polar-embedded aryl stationary phases were synthesized from reactive derivatives of large polycyclic aromatic hydrocarbons (PAHs), including anthracene (three-ring, catacondensed), pyrene (four-ring, pericondensed) and triphenylene (four-ring, fully-benzenoid). These PAHs were functionalized with hydroxymethyl group (PAH-CH2OH), then catalytically converted to carbamates (PAH-CH2OC(=O)NH-R) using isocyanate, and finally covalently grafted onto silica to produce corresponding carbamate-embedded PAH stationary phases. To gain insight into the connection and difference among the attached species, the chromatographic behaviors of these new adsorbents were systematically evaluated in terms of surface coverage, hydrophobic and aromatic features, shape selectivity and charge-transfer property, using different classes of analytes, such as alkylbenzenes, PAH congeners and isomeric multi-substituted benzenes, and the results were further compared with conventional octadecyl ones (C18). The relationships between the shape selectivity and the surface chemistry revealed unique behavioral patterns of theses immobilized conjugated ligands, as well as marked differences amongst them, which formed sharp contrast to the case of C18. The effects of temperature and mobile phase compositions on the shape selectivity were further studied. The charge-transfer characteristics demonstrated the great potential of such polar-embedded PAH materials for highly selective separation of electron-deficient compounds through electron donor-acceptor complexation.