Computational Design Rules for Helical Aromatic Foldamers: $π-π$ Stacking, Solvent Effects, and Conformational Stability

TL;DR

Develops a quantum-chemical framework to design helical aromatic foldamers by quantifying pi-pi stacking, solvent effects, and conformational energetics. Using pyridine-furan and pyridine-EDOT model systems, it shows that solvent dielectric properties modulate stacking interactions and that cis-oriented monomer units favor compact helices. A PES-scanning algorithm maps energy landscapes and enables rapid screening of candidate nanosprings. Demonstrating improved stability with the EDOT analogue, the work provides design rules for engineering bistable nanoscale electronic components with enhanced mechanical robustness.

Abstract

Molecular-scale materials with bistable behavior and tunable properties are increasingly relevant for next-generation nanoscale electronic devices. Helical foldamers are promising candidates, but their structural and mechanical properties are highly sensitive to conformational stability and environmental conditions. A systematic methodology based on quantum-chemical calculations is proposed for assessing solvent-dependent mechanical behavior, combining analysis of $π-π$ stacking interactions, conformational energetics, and environmental effects. Using this methodology we identified simple design principles for the rapid screening of new compounds, allowing evaluation of their conformational stability and effective mechanical rigidity. Applying these principles, we identify a modified helical aromatic foldamer that exhibits improved mechanical and stability characteristics compared to the initial reference compound.

Figures (6)

• Figure 1: (a) Monomeric unit of pyridine-furan, cis conformation, (b) monomeric unit of pyridine-furan, trans conformation, (c) monomeric unit of pyridine-EDOT, cis conformation, (d) optimized geometry of the pyridine-furan oligomer in THF, front view, (e) pyridine-furan heterodimers in two orientations: $0^\circ$ and $180^\circ$, (f) the structural element of the pyridine-furan spiral, (g) steps of the PES scanning algorithm.
• Figure 2: Potential energy profiles of pyridine-furan dimers in $0^\circ$ (orange, yellow) and $180^\circ$ (blue, cyan) orientations in THF and water.
• Figure 3: (a) Initial configuration at $0^\circ$ angle (step 2 of the scanning algorithm: parallel displacement and rotation). PES for the parallel-displaced geometry of furan relative to pyridine in various solvents at the constant coordinate $Z = 3.8$ Å: (b) hexane, (c) benzene, (d) THF, (e) pyridine, (f) methanol, (g) water.
• Figure 4: Dependence of the energy interaction difference between the maximum and minimum on the solvent dielectric constant, with fitted approximation.
• Figure 5: (a) Left: rotational energy profiles of the pyridine-furan monomeric unit around the dihedral angle in neutral, protonated, and excited states in water and THF. Right: molecular geometries at various dihedral angles in the neutral and excited states. The atoms forming the studied dihedral angle are connected by black lines. (b) Left: rotational energy profiles of the pyridine-EDOT monomeric unit around the dihedral angle in neutral, protonated, and excited states in water and THF. Right: molecular geometries at various dihedral angles in the neutral and excited states. The atoms forming the studied dihedral angle are connected by black lines.