Functional group effects on the enthalpy of adsorption for self-assembly at the solution/graphite interface

Heptagonal Molecular Tiling via Self-Assembly of Heptagonal Phenylene-Ethynylene Macrocycle at the Liquid-Solid Interface

The molecular-level scrutinization of on-surface tiling garners considerable interest among scientists. Herein, we demonstrate molecular-level heptagonal tiling using the self-assembly of a heptagonal meta-phenylene-ethynylene macrocycle featuring 14 long alkoxy substituents at the liquid-graphite interface using scanning tunneling microscopy. This heptagonal macrocycle produces an antiparallel pattern at the 1-phenyloctane-graphite interface through van der Waals interactions between the alkoxy chains. This pattern resembles the densely packed pattern of heptagonal tiles, albeit with variations in the orientations and spacing of heptagonal cores owing to intermolecular interactions between the alkoxy chains. Conversely, at the 1,2,4-trichlorobenzene-graphite interface, the heptagonal molecule forms an oblique pattern composed of four independent molecular orientations. This phenomenon arises from core distortion induced by the coadsorption of the solvent molecules within the intrinsic macrocyclic pores. This study elucidates the design strategy - specifically, the choice of heptagonal molecular building block - for heptagonal tiling and fills a crucial gap in the field of two-dimensional crystal engineering.

Three-Dimensional Hollow Reduced Graphene Oxide Tube Assembly for Highly Thermally Conductive Phase Change Composites and Efficient Solar-Thermal Energy Conversion

Due to their extraordinary mechanical strength and electrical and thermal conductivities, graphene fibers and their derivatives have been widely utilized in various functional applications. In this work, we report the synthesis of a three-dimensional (3D) hollow reduced graphene oxide tube assembly (HrGOTA) using the same wet spinning method as graphene fibers. The HrGOTA has high thermal conductivity and displays the unique capability of encapsulating phase change materials for effective solar-thermal energy conversion. The HrGOTA comprises layers of moisture-fused hollow reduced graphene oxide tubes (HrGOTs), whose individual thermal conductivity is up to 578 W m^-1 K^-1. By impregnating 1-octadecanol into HrGOTs, a 1-octadecanol-filled HrGOT phase change composite (PCC) with a latent heat of 262.5 J g^-1 is obtained. This high latent heat results from the interfacial interaction between 1-octadecanol and the reduced graphene oxide tube, as evidenced by the shifts in XRD patterns of 1-octadecanol-filled and 1-octadecanol/multiwalled carbon nanotube-filled HrGOTA samples. In addition, 1 wt % multiwalled carbon nanotubes are added to the PCC to enhance visible light absorption. Because of their high thermal conductivity and visible light absorption rates, these new PCCs display high solar-thermal energy conversion and storage efficiencies of up to 81.7%, commensurate with state-of-the-art carbon-based PCCs but with significantly lower carbon weight percentages.

Trapping a pentagonal molecule in a self-assembled molecular network: an alkoxylated isosceles triangular molecule does the job

We herein report a unique example of on-surface adaptive self-assembly. A pentagon-shaped macrocycle, cyclic [5]meta-phenyleneacetylene [5]CMPA, is trapped by the adaptive supramolecular network formed by an isosceles triangular molecule, alkoxy substituted dehydrobenzo[14]annulene [14]ISODBA at the liquid/graphite interface, leading to a highly ordered and large-area bicomponent self-assembled molecular network (SAMN), as revealed by scanning tunneling microscopy (STM).

Aryl amphiphile shape-directors for shape-controlled synthesis of organic semiconductor particles

Currently, shape- and size-controlled synthesis of organic micro- and nano-particles mostly relies on aliphatic amphiphiles, which lack the structural diversity to provide tunable amphiphile-particle facet interaction energies and result in a limited range of particle shapes. Herein we report the design, synthesis, and utilization of two novel aryl amphiphiles as shape-directors (ShaDs) to obtain particles of different shape. By changing the ShaDs aryl hydrophobe structure, 9,10-diphenylanthracene microcrystals of different shape were obtained with greater than 90% shape yield.

Two-Dimensional versus Three-Dimensional Self-Assembly of a Series of 5-Alkoxyisophthalic Acids

Physisorbed self-assembled monolayers (SAMs) have been suggested as potential models for three-dimensional (3D) crystallization. This work studies the effect of altering the chain length of 5-alkoxyisophthalic acid (C _nISA) on self-assembled morphology in both two-dimensional (2D) and 3D to explore the extent comparisons can be drawn between dimensions. Previous studies of 5-alkoxyisophthalic acid at solid-liquid interfaces (2D) reported different morphologies for C₅ISA and C₆ISA-alkoxy chains on the one hand and C₁₀ISA and C₁₈ISA on the other. Independently, also in 3D a dependence of morphology on chain length has been reported, including an unexpected inclusion of a solvent in the 3D morphology of C₆ISA, while the previous reports of 2D self-assembly were driven only by molecule-molecule and molecule-substrate interactions. However, a complete set of data for comparison has been missing. Here, we report scanning tunneling microscopy (STM) and molecular dynamics simulations performed for C₂ISA self-assembled monolayers (SAMs) and STM imaging of C₆ISA-C₉ISA SAMs, to further examine self-assembly behavior in 2D. In 3D, X-ray diffraction analysis of C₂ISA single crystals was carried out to complete the data set. With a complete set of data, it was observed that regardless of the dimension, short-chain-length C _nISAs formed H-bonding-dominated structures, mid-chain-length C _nISAs exhibited solvent-dependent morphologies, and long-chain-length C _nISAs displayed van der Waals-dominated solvent-independent structures. However, the transition point among morphologies occurred at different chain lengths in 2D and 3D regardless of the dominant interaction. The results of this study inform the design of 2D films and guide the application of knowledge from physisorbed SAMs to 3D systems, including mixed-dimensional (2D/3D) van der Waals heterostructures.

Influence of Multidirectional Interactions on Domain Size and Shape of 2-D Molecular Assemblies

The effect of molecule-molecule interactions on the size and shape of two-dimensional (2-D) ordering domains was investigated using scanning tunneling microscopy (STM) at the liquid/solid interface. Synthesized alkoxybenzene derivatives bearing amide group tend to form very large domains of 2-D orderings (>0.25 μm²), whereas the domain size of corresponding urea derivatives was significantly small in the same condition. The quantitative analysis of the concentration dependence of surface coverage using a nucleation-elongation model suggests that the replacement of amide functionality by urea increased the equilibrium constant of the nucleation process of 2-D self-assembly, which is a key factor for the domain size at the liquid/solid interface. Interestingly, the STM observation revealed that a slight difference of molecular structure influences the shape of 2-D ordering domains, and needle-shaped domains with large aspect ratio around 10 were observed by tuning molecule-molecule intramolecular interactions in 2-D self-assembly formed at a liquid/graphite interface.

Frontiers of supramolecular chemistry at solid surfaces

Supramolecular chemistry on solid surfaces represents an exciting field of research that continues to develop in new and unexpected directions.

Odd–even effect in two dimensions induced by the bicomponent blends of isobutenyl compounds

The bicomponent blends in isobutenyl compounds showed 2D structural modulation due to odd–even effect as well as blend ratio-dependent 2D structural change.

Adsorption Behaviors of Mixed Monolayers of n-Alkanes at the Liquid-Solid Interface

To understand the self-assembly of monolayers at the liquid-solid interface, a thermodynamic model, which describes the contributions of the molecular interactions, is essential. We present an adapted Zimm-Bragg model of the cooperativity transitions for determining the Gibbs free energy for self-assembly at the liquid-solid interface. Scanning tunneling microscopy was used to observe the monolayers formed on graphite from phenyloctane solutions of binary mixtures of n-hexacosane (C26H54) and n-tetratriacontane (C34H70). This revealed that the sharp transition in the monolayers from the full surface coverage of the long-chain alkane, which is adsorbed preferentially, to the full coverage of the short-chain alkane is a function of the mixture composition. The model allows for the estimation of the free-energy changes associated with the difference in the alkyl chain length and the interface between the two different alkane regions in the monolayers. It is also suitable for understanding more complex systems that exhibit intermolecular interactions.

Kinetic and thermodynamic processes of organic species at the solution-solid interface: the view through an STM

A focused review is presented on the evolution of our understanding of the kinetic and thermodynamic factors that play a critical role in the formation of well ordered organic adlayers at the solution-solid interface. While the current state of knowledge is in the very early stages, it is now clear that assumptions of kinetic or thermodynamic control are dangerous and require careful confirmation. Equilibrium processes at the solution-solid interface are being described by evolving thermodynamic models that utilize concepts from the thermodynamics of micelles. A surface adsorption version of the Born-Haber cycle is helping to extract the thermodynamic functions of state associated with equilibrium structures, but only a very few systems have been so analyzed. The kinetics of surface phase transformation, especially for polymorphic phases is in an early qualitative stage. Adsorption and desorption kinetics are just starting to be measured. The study of kinetics and thermodynamics for organic self-assembly at the solution-solid interface is experiencing very exciting and rapid growth.