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

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