Interaction mechanism of anthracene with benzoic acid and its derivatives

Interaction mechanism of anthracene, one of the typical polycyclic aromatic hydrocarbons, with benzoic acid and its hydroxyl-substituted derivatives, o-hydroxylbenzoic acid and p-hydroxylbenzoic acid, were studied using FTIR, UV and fluorescence spectra. The experiments confirmed that there was a specific and oriented interaction between anthracene and the aromatic carboxylic acids, and the bonding mode depended on both the chemical structure of reactants and acidity of solution. The π-H hydrogen bond played a main role in the interaction between anthracene and the aromatic carboxylic proton of benzoic acid or o-hydroxylbenzoic acid when pH≤pK_a, and the π-π electron donor-acceptor (EDA) interaction increasingly became the main binding mode when pH>pK_a. The decrease of interaction intensity of benzoic acid was observed by introducing hydroxyl at its ortho position. The special D-π-A structure of p-hydroxylbenzoic acid made it easy to form the planar multi-molecule congeries that could interact with anthracene, so the interaction between anthracene and p-hydroxylbenzoic acid always followed the π-π EDA model no matter the solution acidity. For p-hydroxylbenzoic acid, the π-π interaction mode remained unchanged when pH increased from 2.0 to 10.0, and the binding intensity was higher than that between benzoic acid and anthracene because of the formation of the multi-molecule congeries.