Self-assembled monolayers of aromatic thiols stabilized by parallel-displaced pi-pi stacking interactions

Area of Science:

• Supramolecular chemistry
• Surface science
• Organic electronics

Background:

• Pi-pi stacking interactions are crucial for biological macromolecules like DNA and proteins.
• The role of pi-pi interactions in self-assembled monolayers (SAMs) of aromatic thiols is less understood.
• Anthracene derivatives offer a platform to study pi-pi stacking in SAMs.

Purpose of the Study:

• To investigate the role of parallel-displaced pi-pi stacking in the self-assembly of anthracene-based thiols on Au(111).
• To explore how functional groups (NO2, COOH) and spacers influence monolayer structure.
• To understand the interplay between pi-pi stacking and other intermolecular forces in SAMs.

Main Methods:

• Synthesis of four anthracene-based thiols with varying functional groups.
• Formation and characterization of self-assembled monolayers on Au(111).
• High-resolution scanning tunneling microscopy (STM) for structural analysis.

Main Results:

• All synthesized aromatic thiols formed long-range-ordered monolayers on Au(111).
• Despite functional group variations, a consistent fundamental packing structure was observed across all SAMs.
• STM observations supported space-filling models dominated by parallel-displaced pi-pi stacking.

Conclusions:

• Parallel-displaced pi-pi stacking is the primary driving force for the self-assembly of these anthracene-based thiols.
• The fundamental packing structure of the monolayers is robust and largely independent of the specific functional groups present.
• This study provides insights into the design principles for creating ordered SAMs with predictable structures.