Atomic-Scale Imaging Reveals Polar-π Interactions in Two-Dimensional Molecular Superlattices.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Nanotechnology

Background:

• Controlling the atomic-level coassembly of synthetic oligomers into binary superlattices remains a significant challenge.
• Peptoids, as sequence-defined peptidomimetics, offer a platform for precise molecular design.

Purpose of the Study:

• To develop a strategy for programming polar-π interactions in oligomeric peptoids to achieve controlled formation of homogeneous two-dimensional (2D) superlattices.
• To investigate how different aromatic side chains influence superlattice crystal motifs and thermal stability.

Main Methods:

• Introduction of N-2-phenylethyl and N-(2-perfluorophenyl)ethyl side chains at defined positions in peptoid sequences.
• Analysis of superlattice formation and crystal motifs using cryogenic transmission electron microscopy (cryo-TEM).
• Computational studies including molecular dynamics simulations and density functional theory (DFT) calculations.

Main Results:

• Peptoid systems with single aromatic side chains formed parallel V-shaped motifs driven by π-π interactions.
• Coassembly of peptoids with both aromatic side chains resulted in antiparallel V-shaped superlattices with enhanced thermal stability, driven by polar-π interactions.
• Cryo-TEM and computational methods confirmed the dominance of polar-π interactions in dictating superlattice structure and stability.

Conclusions:

• A design principle for binary coassembly using sequence-defined oligomers was established, enabling control over unit cell geometry and lattice stability.
• Programming aromatic side chain polarization and sequence control allows for precise manipulation of 2D soft materials.
• This approach facilitates the design of functional 2D soft materials with enhanced thermal stability and controlled molecular registration.