Physics Department - Induced Fit of Adsorbates inside Nanometer-Sized Quantum Confinements

Abstract
Host-guest architectures provide ideal systems to investigate site-specific physical and chemical effects. Condensation events in nanometer sized confinements are particularly interesting for the investigation of inter-molecular and molecule-surface interactions. They may be accompanied by conformational adjustments representing induced-fit packing patterns. Here, we report that the symmetry of small clusters of cycloalkane molecules, formed by condensation, their registry with the substrate, their structure as well as their adsorption height is characteristically modified by their packing in confinements. While cyclopentane and cycloheptane display cooperativity upon filling of the hosting pores, cyclooctane and to a lesser degree cyclohexane diffusively re-distribute to more favored adsorption sites. The reported dynamicity of cyclooctane is surprising at 5K given the cycloalkane melting point above 0°C. The site-specific modification of the interaction and behavior of adsorbates in confinements plays a crucial role in many applications of porous materials, e.g. as gas storage agents or catalysts and bio-catalysts.

Image

Fig. 1.) Adsorption of cyclooctane into the confinements provided by an on-surface metal organic network: One to three molecules rest on the bottom substrate within the confinement. As four molecules gather in a single pore, they are lifted into a dynamic adsorption mode, -- unexpected at 5K substrate temperature for a molecule that melts at ~300 K higher temperatures.
 

Reference
[1] A. Ahsan et al., J. Phys. Chem. Lett. 2022, 13, 7504−7513