Dynamic Imaging of Solvent Exchange-Induced Interlayer Shifting in Single Two-Dimensional Covalent Organic Frameworks

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Interlayer shifting in 2D covalent organic frameworks (COFs) significantly impacts their sorption and catalytic performance.
• Existing analytical methods provide static, averaged data from bulk samples, limiting insight into dynamic interlayer processes in individual COFs.

Purpose of the Study:

• To develop and apply a real-time imaging technique for observing solvent exchange-induced interlayer shifting in single 2D COFs.
• To investigate the dynamics, heterogeneity, and influencing factors of interlayer shifting in response to solvent exchange.

Main Methods:

• Utilized in situ dark-field optical microscopy (DFM) for real-time dynamic imaging of individual 2D COFs.
• Employed grayscale intensity analysis of DFM images to quantify interlayer shifting and pore size changes.
• Performed theoretical simulations to elucidate the governing factors and thermodynamic pathways of interlayer shifting.

Main Results:

• Successfully visualized solvent exchange-induced interlayer shifting in triphenylbenzene (TPB)-based COFs.
• Observed an increase in pore size (from quasi-AB to AA stacking) facilitating guest molecule accommodation and increased scattering intensity.
• Demonstrated significant particle-to-particle heterogeneity in shifting dynamics, influenced by solvent viscosity and interlayer interaction strength.

Conclusions:

• The developed DFM imaging methodology enables direct observation of dynamic interlayer shifting in single 2D COFs.
• Solvent exchange triggers interlayer shifting, altering pore size and impacting COF functionality.
• Theoretical simulations confirm that stacking energies and thermodynamic preferences govern the shifting process during solvent exchange.