All-carbon, neutral analogue of ExBox4+: A DFT study of polycyclic aromatic hydrocarbon binding

To assess the role that electrostatic interactions play in the binding of polycyclic aromatic hydrocarbons within ExBox(4+) 1, we report ωB97X-D/6-311G(d,p) computations of the binding of five small linear acenes with the hydrocarbon neutral analogue 5 in both the gas phase and acetonitrile solution. The terphenyl units of 5 are less bowed outward than are the ExBIPY units of 5, due to the lack of charge repulsion. This manifests in a much smaller ring strain energy in 5 than 1. The acenes bind to both 1 and 5 with increasing affinity as the size of the guest increases. The affinity of the PAHs to 1 is greater than the affinity to 5, though the difference in the binding enthapies to 1 and 5 is relatively small, ranging from 2.4 to 9.8 kcal mol(-1). Electrostatics account for only 10-20% of the total binding energy.