Two-dimensional crystallization of nitrobenzene on a monolayer of stearic acid characterized by scanning tunnelling microscopy

Formation of Supramolecular Heterostacks at the Liquid-Solid Interface: Impact of Symmetry Mismatching on Structural Growth

The construction of intricate three-dimensional (3D) nanoarchitectures on surfaces through molecular self-assembly attracts attention not only from a crystal engineering viewpoint but also because of its potential in a range of applications, given the current interest in van der Waals heterostructures. We herein report the formation of porous structures on alkane buffer layers on graphite. A dehydrobenzo[12]annulene (DBA) derivative having six decyloxy chains forms hexagonal structures on n-pentacontane and n-hexacontane buffer layers through van der Waals interactions at the 1-octanoic acid/graphite interface. The structural features are very similar to those on the graphite surface, except for the slight structural distortion, which is attributed to the p2 symmetry of the buffer layer underneath. Moreover, based on the observation of small clusters of the DBA molecules, we discussed the nucleation and structural growth of the DBA network on a buffer layer. Finally, a hierarchical multicomponent structure was formed through the coadsorption of a heteromolecular cluster formed by a hydrogen-bonded isophthalic acid cyclic hexamer hosting a coronene molecule on the buffer layer. This study on supramolecular heterostacks provides insights into the construction of intricate 3D nanoarchitectures using self-assembly at interfaces.

Growth of a self-assembled monolayer decoupled from the substrate: nucleation on-command using buffer layers

Structural polymorphism is ubiquitous in physisorbed self-assembled monolayers formed at the solution-solid interface. One of the ways to influence network formation at this interface is to physically decouple the self-assembled monolayer from the underlying substrate thereby removing the influence of the substrate lattice, if any. Here we show a systematic exploration of self-assembly of a typical building block, namely 4-tetradecyloxybenzoic acid at the 1-phenyloctane-graphite interface in the presence and in the absence of a buffer layer formed by a long chain alkane, namely n-pentacontane. Using scanning tunneling microscopy (STM), three different structural polymorphs were identified for 4-tetradecyloxybenzoic acid at the 1-phenyloctane-graphite interface. Surprisingly, the same three structures were formed on top of the buffer layer, albeit at different concentrations. Systematic variation of experimental parameters did not lead to any new network in the presence of the buffer layer. We discovered that the self-assembly on top of the buffer layer allows better control over the nanoscale manipulation of the self-assembled networks. Using the influence of the STM tip, we could initiate the nucleation of small isolated domains of the benzoic acid on-command in a reproducible fashion. Such controlled nucleation experiments hold promise for studying fundamental processes inherent to the assembly process on surfaces.

Controlled templating of porphyrins by a molecular command layer

The copper porphyrin (5,10,15,20-tetraundecylporphyrinato)copper(II) can be templated in a well-defined arrangement using p-(hexadecyloxycarbonyl)phenylacetylene as a command layer on graphite. The bicomponent system was characterized at the submolecular level at a solid/liquid interface by scanning tunneling microscopy (STM). It is proposed that the layer of copper porphyrins is templated on top of the command layer in a hierarchical fashion, via a combination of intermolecular π-π stacking and van der Waals interactions. A very subtle effect, i.e., a superstructure in the alkyl chain region of the phenylacetylene monolayers, was identified as a decisive factor for the templating process.

Driving forces underlying the formation of chiral domains of fluorinated diacids on graphite

The role of intermolecular interactions, molecule-substrate interactions, and molecular chirality in the construction of 2-D surface architectures is the subject of much current interest. A racemic mixture of long chain hydrocarbons was synthesized with terminal carboxylic acid functionalities at each end and two amide linkages in the central region of the molecule on either side of two F-containing chiral centers. Using scanning tunnelling microscopy (STM), we have examined how the functionality of these molecules influences their self-assembly on a highly oriented pyrolytic graphite (HOPG) surface. The key factors determining the nature of ordered domains have been identified.