Hydrated cation-π interactions of π-electrons with hydrated Li+, Na+, and K+ cations.

Cation–π interactions are essential for many chemical, biological, and material processes, and these processes usually involve an aqueous salt solution. However, there is still a lack of a full understanding of the hydrated cation–π interactions between the hydrated cations and the aromatic ring structures on the molecular level. Here, we report a molecular picture of hydrated cation–π interactions, by using the calculations of density functional theory (DFT). Specifically, the graphene sheet can distort the hydration shell of the hydrated K+ to interact with K+ directly, which is hereafter called water–cation–π interactions. In contrast, the hydration shell of the hydrated Li+ is quite stable and the graphene sheet interacts with Li+ indirectly, mediated by water molecules, which we hereafter call the cation–water–π interactions. The behavior of hydrated cations adsorbed on a graphene surface is mainly attributed to the competition between the cation–π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated cations adsorbed onto the graphene surface.