Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface

We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/solid interface. For this purpose, a dehydrobenzo[12]­annulene (DBA) derivative, <b>DBA-TeEG</b>, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by <i>p</i>-phenylene linkers was synthesized. As a reference host molecule, <b>DBA-C10,</b> having nonpolar C₁₀ alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene–ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, <b>PEM-TEG</b> and <b>PEM-C6</b>, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite interface revealed that <b>PEM-TEG</b> was immobilized in the pores formed by <b>DBA-TeEG</b> at higher probability because of electrostatic interactions such as dipole–dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to <b>PEM-C6</b> with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by <b>DBA-C10</b> was used, however, only phase separation and preferential adsorption were observed; virtually no host–guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface