Carboxylic acids: versatile building blocks and mediators for two-dimensional supramolecular self-assembly

Area of Science:

• Supramolecular chemistry
• Surface science
• Materials science

Background:

• Two-dimensional (2D) self-assembly of organic molecules at interfaces is crucial for advanced materials.
• Carboxylic groups are key functional groups for driving self-assembly due to their hydrogen bonding capabilities.

Purpose of the Study:

• To investigate the 2D supramolecular self-assembly of carboxylic-functionalized molecules at the liquid-solid interface.
• To explore the influence of molecular structure and external conditions on self-assembled monolayer formation.
• To understand the thermodynamic control governing interfacial self-assembly.

Main Methods:

• Scanning tunneling microscopy (STM) for high-resolution real-space imaging.
• Analysis of crystallographic information (lattice parameters, molecular arrangement) from STM data.
• Systematic variation of molecular structures, solvents, and concentrations.

Main Results:

• Well-ordered and stable 2D self-assembled monolayers were formed.
• Carboxylic groups facilitate reliable intermolecular cross-linking via hydrogen bonds.
• Both molecular structure and external conditions (solvent, concentration) significantly impact self-assembly.
• Thermodynamic control was observed, with surface adsorption being in equilibrium with the solution phase.

Conclusions:

• Carboxylic-functionalized molecules are excellent building blocks for creating stable 2D self-assembled monolayers at liquid-solid interfaces.
• STM is a powerful tool for characterizing the crystallographic details of these assemblies.
• Understanding the thermodynamic control allows for precise steering of self-assembly processes.