Unexpected Influence of Substituents on the Binding Affinities of Polycyclic Aromatic Hydrocarbons with a Tetra-Au(I) Metallorectangle

A tetragold supramolecular organometallic cage constructed with two pyrene-bis­(imidazolylidene) ligands and two carbazolyl-bis­(alkynyl) linkers (1) was studied as a host for a series of substituted polycyclic aromatic hydrocarbons (PAHs). For the two smaller PAHs used (2-naphthalenol and 1-pyrenemethanol), the presence of the −OH groups at the periphery of the molecules did not enhance the binding affinity of the guest, in comparison with the unsubstituted PAHs. This observation indicated no hydrogen bonding of these two guests with the NH of the carbazole linker, as well as negligible dispersive interactions of the substituents with the π system of 1. In the case of 3-perylenemethanol, the CH2OH group produced a significant increase in the binding affinity vs that of perylene. Similarly, 3-methylperylene shows an increased binding affinity in comparison to perylene. MN15-L/def2-QZVP calculations gave Gibbs reaction energies for the displacement of perylene from the host by the substituted perylenes becoming more exergonic in the order −1.6 (3-methylperylene) > −4.3 (3-ethylperylene) > −4.5 kcal/mol (3-perylenemethanol). The experimental and DFT results indicate that the peripheral dispersive interactions can make a significant contribution to the host–guest bonding energy, in addition to the conventional π–π stacking interactions. Our work highlights the importance of dispersive interactions in the contribution to the binding affinity of host–guest chemistry complexes.