Significant conformational changes associated with molecular transport in a crystalline solid

Area of Science:

• Solid-state chemistry
• Materials science
• Supramolecular chemistry

Background:

• Crystalline urea inclusion compounds exhibit one-dimensional tunnels capable of hosting guest molecules.
• Guest molecule transport and exchange are fundamental processes in these materials.
• Understanding molecular dynamics within these confined spaces is crucial for materials design.

Purpose of the Study:

• To investigate the in situ molecular transport of guest molecules within urea inclusion compound tunnels.
• To elucidate the conformational changes of guest molecules during guest exchange.
• To explore the fundamental aspects of molecular transport in confined crystalline environments.

Main Methods:

• Confocal Raman microspectrometry was employed as an in situ probe.
• Raman spectra were recorded as a function of position and time along the tunnel axis.
• Guest exchange was performed by introducing pentadecane to displace 1,8-dibromooctane.

Main Results:

• The transport process induced significant conformational changes in the original 1,8-dibromooctane guest molecules.
• A notable increase in the gauche end-group conformation of 1,8-dibromooctane was observed at the boundary region.
• The dynamics of guest molecule displacement were directly visualized and analyzed.

Conclusions:

• Confocal Raman microspectrometry effectively probes guest molecule transport and conformational dynamics in crystalline inclusion compounds.
• Molecular transport is intrinsically linked to conformational rearrangements of guest molecules within confined tunnels.
• The findings provide insights into the mechanisms governing molecular motion in ordered solid-state materials.