Self-assembly of bicomponent molecular monolayers: adsorption height changes and their consequences

Area of Science:

• Surface Science and Nanotechnology
• Organic Electronics
• Supramolecular Chemistry

Background:

• Donor-acceptor molecular systems are crucial for organic electronic devices.
• Self-assembly on surfaces offers precise control over molecular arrangement.
• Hydrogen bonding is a key interaction for directing molecular self-assembly.

Purpose of the Study:

• To investigate the self-assembly of copper phthalocyanine (CuPc) and perfluoropentacene (PFP) mixtures on noble metal surfaces.
• To understand the role of intermolecular interactions, specifically C-H ⋯ F bonds, in dictating molecular arrangement.
• To analyze the impact of molecular arrangement on molecule-substrate distances and electronic properties.

Main Methods:

• Codeposition of CuPc and PFP on noble metal (111) surfaces.
• Precise measurement of molecule-substrate adsorption heights using surface science techniques.
• Work function measurements to investigate electronic properties, including interface dipole.

Main Results:

• An ordered mixed layer with maximized donor-acceptor contact area was formed.
• Perfluoropentacene (PFP) exhibited significantly larger adsorption heights than copper phthalocyanine (CuPc) in the mixed layer.
• The height difference between PFP and CuPc increased in the blend compared to single-component layers, contrary to expectations for enhanced hydrogen bonding.

Conclusions:

• The self-assembly of CuPc and PFP on noble metal surfaces leads to an unexpected increase in PFP adsorption height.
• This suggests a reduced interaction of PFP with the substrate in the mixed layer, despite the presumed driving force of C-H ⋯ F hydrogen bonds.
• The observed structural changes influence electronic properties, such as the interface dipole, highlighting the complexity of molecular self-assembly in blends.