Directed Assembly of Nonplanar TPE-Based Esters via C-H···O═C Hydrogen Bonds at the Solution/Solid Interface

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Chemistry

Background:

• Nonconventional hydrogen bonds enable the formation of dynamic, robust hydrogen-bonded organic frameworks (HOFs).
• Precise control over HOF structures necessitates a deep understanding of molecular geometrical ordering.
• Tetraphenylethene (TPE)-based derivatives are versatile building blocks for supramolecular assemblies.

Purpose of the Study:

• To investigate the role of C-H···O═C hydrogen bonding in the self-assembly of TPE-based methyl ester derivatives.
• To explore the molecular ordering of these derivatives at the solution/solid interface and in the solid state.
• To elucidate the interplay between molecular geometry and hydrogen bonding in HOF formation.

Main Methods:

• Scanning tunneling microscopy (STM) for surface analysis.
• X-ray crystallography for solid-state structural determination.
• Analysis of methyl ester derivatives of TPE, including Me4TPE, Me2TPDC, and Me4ETTC.

Main Results:

• TPE-based esters form robust monolayer assemblies on highly ordered pyrolytic graphite (HOPG) surfaces.
• Assemblies are stabilized by C-H···O═C hydrogen bonds, π-π interactions, and molecule-substrate interactions.
• Identified cyclic, bifurcated, and three-centered C-H···O═C hydrogen bonding motifs with similar conformations in both solution and solid states.

Conclusions:

• C-H···O═C hydrogen bonds are crucial for the ordered assembly of TPE-based methyl esters.
• Molecular geometry and energetic factors collectively dictate the extent and nature of hydrogen bonding in these HOFs.
• This study provides insights into the rational design and manipulation of HOFs for advanced material applications.