Shape-Memory Effect Triggered by π-π Interactions in a Flexible Terpyridine Metal-Organic Framework

Area of Science:

• Materials Science
• Chemistry

Background:

• Shape-memory materials, including polymers and alloys, recover their original form after deformation via external stimuli.
• In metal-organic frameworks (MOFs), shape-memory refers to a switchable framework's ability to retain its reopened pore structure after initial transformation.

Purpose of the Study:

• To describe a novel flexible terpyridine MOF with shape-memory characteristics.
• To categorize shape-memory MOFs based on the transformability of their gas-free reopened pore phase.
• To highlight the importance of multicycle physisorption for studying dynamic porous materials.

Main Methods:

• Synthesis of a novel flexible terpyridine MOF.
• In situ experimental studies including Single-Crystal X-ray Diffraction (SC-XRD) and Powder X-ray Diffraction (PXRD).
• Density Functional Theory (DFT) energetic calculations and literature review.

Main Results:

• A novel flexible terpyridine MOF was synthesized, which transforms into a nonporous structure upon desolvation.
• This MOF reopens into a shape-memory phase when exposed to CO2 at 195 K.
• A classification of shape-memory MOFs into responsive and nonresponsive categories was proposed based on framework transformability.

Conclusions:

• The study presents a new MOF exhibiting CO2-triggered shape-memory behavior.
• A framework for classifying shape-memory MOFs is proposed, aiding in material discovery.
• Multicycle physisorption is crucial for understanding dynamic porous materials like MOFs and COFs.