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.