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

Regulating Rotational Dynamics of Co-Adsorbed Guest Molecules via Halogen Bonds in Functionalized Pores of Self-Assembled Molecular Networks at the Liquid-Solid Interface

Understanding and controlling molecular rotation on surfaces is crucial for the development of molecular-scale artificial motors that operate at interfaces. Herein, it is reported the successful co-adsorption of guest molecules within the functionalized 2D pores of self-assembled molecular networks (SAMNs) through directional halogen bonding, as confirmed by scanning tunneling microscopy. Specifically, the porous SAMN formed by dehydrobenzo[12]annulene derivative DBA-Py with a pyridyl group at the termini of its three alkoxy chains, hosts an iodinated trigonal guest molecule, tris(4-iodophenyl)benzene (TIB), through a halogen bond between the nitrogen and iodine atoms. Within the pores, the TIB molecule exhibits rotational motion, preferentially residing at two locations. In contrast, within the pores formed by a mixture of DBA-Py and DBA-Ph, where DBA-Ph features three phenyl groups instead of pyridyl groups, the guest molecule preferentially resides in a single location. This behavior is attributed to the reduced number of energy minima within the pores owing to the decreased number of pyridyl units. Statistical analysis of the guest orientation suggests that the on-surface arrangement of DBA-Py and DBA-Ph is influenced by the guest molecule. This modular approach using functionalized pores in SAMNs provides an effective strategy for controlling molecular rotational behavior.

Self-Assembled Monolayers of Gemini-Type Amphiphilic Hexabenzocoronenes on Gold: Contribution of Their Triethylene Glycol Side Chains to Self-Assembly Formation

We report on a two-dimensional self-assembled structure of a supramolecule with hydrophilic oligoethylene glycol (EG) units, which are capable of stronger electrostatic interactions than van der Waals (vdW) interactions between alkyl chains. For this purpose, hexabenzocoronene (HBC) with two hydrophobic dodecyl chains on one side of the HBC core and two hydrophilic triethylene glycol (TEG) chains on the other side of the HBC core (HBCGemini) and HBCGemini with a trinitrofluorenone (TNF) added to the end of one TEG chain (HBCTNFGemini) were employed. Scanning tunneling microscopy (STM) revealed the presence of multiple two-dimensional self-assembled structures in each of HBCGemini and HBCTNFGemini deposited on the gold substrate in vacuum. The role of polar functional groups in these observations is discussed based on semiempirical molecular orbital simulations. Two types of 2D organized structures of HBC-TEG were observed: one with rectangular and relatively dense unit cells and the other with nearly square and relatively sparse unit cells. In both organized structures, the phenyl group TEG units and alkyl chains were considered to be the main molecular interactions with each other. On the other hand, in HBCTNFGemini, three types of organized structures were observed, which could be explained by the mechanism of interdigitation of the TEG-containing side-chain moieties to form a dimeric core. The EG units are more flexible than the alkyl chains and thus can interact flexibly with the hydrophobic HBC core, and the glycol side chains facilitate the intermolecular interactions as well as the alkyl chains.

One-shot preparation of topologically chimeric nanofibers via a gradient supramolecular copolymerization

Supramolecular polymers have emerged in the last decade as highly accessible polymeric nanomaterials. An important step toward finely designed nanomaterials with versatile functions, such as those of natural proteins, is intricate topological control over their main chains. Herein, we report the facile one-shot preparation of supramolecular copolymers involving segregated secondary structures. By cooling non-polar solutions containing two monomers that individually afford helically folded and linearly extended secondary structures, we obtain unique nanofibers with coexisting distinct secondary structures. A spectroscopic analysis of the formation process of such topologically chimeric fibers reveals that the monomer composition varies gradually during the polymerization due to the formation of heteromeric hydrogen-bonded intermediates. We further demonstrate the folding of these chimeric fibers by light-induced deformation of the linearly extended segments.