Molecular Interactions and Layer Stacking Dictate Covalent Organic Framework Effective Pore Size

Interactions
among ions, molecules, and confining solid surfaces
are universally challenging and intriguing topics. Lacking a molecular-level
understanding of such interactions in complex organic solvents perpetuates
the intractable challenge of simultaneously achieving high permeance
and selectivity in selectively permeable barriers. Two-dimensional
covalent organic frameworks (COFs) have demonstrated ultrahigh permeance,
high selectivity, and stability in organic solvents. Using reactive
force field molecular dynamics modeling and direct experimental comparisons
of an imine-linked carboxylated COF (C-COF), we demonstrate that unprecedented
organic solvent nanofiltration separation performance can be accomplished
by the well-aligned, highly crystalline pores. Furthermore, we show
that the effective, as opposed to designed, pore size and solvated
solute radii can change dramatically with the solvent environment,
providing insights into complex molecular interactions and enabling
future application-specific material design and synthesis.