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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
Published on: August 2, 2012
Supramolecular staircase via self-assembly of disklike molecules at the solid-liquid interface
P Samorí1, A Fechtenkötter, F Jäckel
1Department of Physics, Humboldt University Berlin, Invalidenstrasse 110, 10115 Berlin, Germany.
Journal of the American Chemical Society
|November 15, 2001
Summary
Hexabenzocoronene (HBC) derivatives self-assemble into ordered 2D arrays on graphite. The presence of phenylene spacers and chiral side chains influences molecular arrangement and contrast in scanning tunneling microscopy (STM) imaging.
Area of Science:
- Supramolecular chemistry
- Materials science
- Surface science
Background:
- Hexabenzocoronenes (HBCs) are discotic molecules known for self-assembly into ordered structures.
- Controlling molecular arrangement at interfaces is crucial for developing advanced materials.
- The influence of side-chain chirality and molecular architecture on self-assembly is an active area of research.
Purpose of the Study:
- To investigate the self-assembly behavior of soluble HBC derivatives with varying side chains and phenylene spacers.
- To understand how molecular structure, including chirality, affects the ordering and electronic properties of HBC monolayers on highly oriented pyrolytic graphite (HOPG).
- To explore the potential for creating novel supramolecular architectures with tunable properties.
Main Methods:
- Synthesis of soluble HBC derivatives with optically active and racemic side chains, with and without phenylene spacers.
- Assembly of HBC derivatives at the solution-graphite interface.
- Molecularly resolved scanning tunneling microscopy (STM) to image the self-assembled monolayers.
- Analysis of STM contrast variations to infer molecular conformation and arrangement.
Main Results:
- All studied HBC derivatives self-assembled into quasi-2D oriented crystalline arrays on HOPG.
- HBCs with phenylene spacers exhibited different STM contrasts for aromatic cores within a monolayer, unlike simple alkyl-substituted HBCs.
- Optically active phenylene-alkyl-substituted HBCs formed a regular superstructure with three distinct molecular positions, resembling a staircase.
- Racemic HBC derivatives showed random distribution of contrasts, while optically active ones displayed periodical arrangements.
Conclusions:
- The phenylene spacer disrupts molecular planarity, leading to varied conformations and distinct equilibrium positions on the surface.
- Chirality of side chains plays a critical role in dictating the periodicity and order of the self-assembled superstructure.
- The observed self-assembly is governed by a complex interplay of intra-, inter-, and interfacial interactions.
- These findings open possibilities for investigating molecule-substrate coupling using scanning tunneling spectroscopy (STS) and potential STM tip-induced molecular switching.
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