From Foldable Open Chains to Shape-Persistent Macrocycles: Synthesis, Impact on 2D Ordering, and Stimulated...

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Electronics

Background:

• Small molecule self-assembly is key for ordered organic films in chemical and electronic applications.
• Precise control over intermolecular interactions is crucial for programming molecular structure and function.
• Bis(triazolo)benzene-based molecules offer a tunable platform for surface self-assembly studies.

Purpose of the Study:

• To design and synthesize novel bis(triazolo)benzene-based π-conjugated molecules.
• To investigate the structure-dependent self-assembly behavior of these molecules on surfaces.
• To explore the influence of molecular structure and peripheral groups on surface ordering and response to stimuli.

Main Methods:

• Synthesis of bis(triazolo)benzene derivatives using late-stage C-C cross-coupling.
• Scanning tunneling microscopy (STM) for analyzing molecular self-assembly at surfaces.
• Comparative studies of linear precursors and cyclized macrocycles with varying peripheral groups (alkyl vs. oligo ethylene glycol).

Main Results:

• Distinct self-assembly behaviors observed based on molecular backbone flexibility and peripheral group chemistry.
• Alkyl chains promoted interdigitated structures, while oligo ethylene glycol (OEG) chains led to more densely packed π-cores.
• Cyclized macrocycles showed faster self-assembly kinetics than linear precursors due to restricted conformational freedom.
• STM tip perturbation and cosolutes significantly affected self-assembly kinetics and surface patterning.

Conclusions:

• Molecular design, including conformational restriction and peripheral group selection, enables precise control over surface self-assembly.
• Weak noncovalent interactions in solution can be amplified for confined molecules on 2D surfaces, leading to robust ordering.
• These findings provide insights into programming molecular interactions for advanced organic materials and surface patterning.