We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/solid interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration it formed a high-density hexagonal structure in which alkyl chains are not adsorbed on the surface (dense hexagonal structure). In the dense hexagonal structure, macrocyclic cores are linked by hydrogen bonds between the ester carbonyl oxygen and the aromatic hydrogen atoms of the neighboring macrocycles. The packing geometries of loose hexagonal structures of PEM-C6 and PBM-C8 are different due to the different distance between the attachment of the alkyl ester groups which are located in confined space. On the other hand, PEM-TEG and PBM-TEG formed dense hexagonal structures, similar to PBM-C8 at high concentration, with their TEG units not adsorbed on the surface.

We present here the construction of a self-assembled two-dimensional network at the liquid/solid interface using a hexagonal pyridine macrocycle which binds an organic cation in its intrinsic porous space by electrostatic interactions. For this purpose, a hexagonal pyridinylene-butadiynylene macrocycle (PyBM) having six octyloxymethyl groups, PyBM-C8, was synthesized. As guests, tropylium (Tr) tetrafluoroborate and trioxatriangulenium (TOTA) hexafluorophosphate were used. In this study, we focused on (i) the network patterns of PyBM-C8 which change in response to its concentration and (ii) the position of the guest immobilized in the porous space of the macrocycle. Scanning tunneling microscopy (STM) observations at the interface of 1,2,4-trichlorobenzene (TCB) and highly oriented pyrolytic graphite (HOPG) revealed that PyBM-C8 formed four different polymorphs, oblique, loose hexagonal, linear, and rectangular, depending on the solute concentration and annealing treatment. Solvent TCB molecules are likely co-adsorbed not only the intrinsically porous space of PyBM-C8 (internal TCB) but also the space outside of the macrocycle between its alkyl chains (external TCB) in most of the cases. Upon adding the guest cation, whereas small Tr was not visualized in the pore due to size mismatching, larger TOTA was clearly observed in each pore. In addition, based on high resolution STM images of the rhombus packing pattern of PyBM-C8, we 3 revealed experimentally that TOTA was placed at an off-center position of the deformed hexagonal macrocyclic core in the rhombus pattern. Based on the molecular mechanics calculations, we hypothesize that the off-center location of TOTA is due to deformation of the hexagonal macrocycle through interaction with two external TCB molecules located at opposite edges of the macrocyclic core. Symmetry-breaking of the macrocyclic host framework induced by co-adsorbed surrounding solvent molecules thus play a significant role in host-guest complexation 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, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C 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, PEM-TEG and PEM-C6, 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 PEM-TEG was immobilized in the pores formed by DBA-TeEG 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 PEM-C6 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 DBA-C10 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.