Interaction Force Landscapes within and Surrounding Hydrophobic Nanopockets Revealed by Three-Dimensional Scanning Atomic Force Microscopy

The precise design of 2D supramolecular assemblies constructed from 3D organic molecules on the surfaces of sp2 carbon materials is expected to advance the development of functional materials and devices. Supramolecular assemblies containing nanopockets can exhibit functions such as molecular recognition; however, directly probing and elucidating the intermolecular interactions and the associated interaction energies on the single-nanopocket scale remain a significant challenge. In this study, subnanometer resolution atomic force microscopy (AFM) was used to reveal that a tetrakis(4-ethynylphenyl)methane derivative, modified with a single oligo(ethylene glycol) chain and used as an organic building block, formed high-density hydrophobic nanopockets in its monolayer through CH−π interactions between the compact ethynyl termini. Furthermore, three-dimensional scanning AFM (3D-AFM) measurements revealed a distinct distribution of attractive forces within the hydrophobic nanopockets, attributed to a decrease in water density arising from confinement effects by nanometer-sized spaces. Importantly, 3D-AFM imaging, which can spatially resolve the distribution of interaction forces with piconewton-level sensitivity, allows the construction of interaction energy landscapes at the single-nanopocket level, which is not possible using established methods. This capability of 3D-AFM imaging is expected to advance the microscopic understanding of molecular recognition mechanisms in host–guest systems and porous materials.