Synergistic Structural Degradation and Electronic Penalties in Fluorinated Carbazole-Based Nanoporous Organic...

Fluorination is recognized as an effective approach for improving gas separation in porous materials. However, its concomitant effects on the material's physical architecture are often overlooked. Here, we systematically investigate the consequences of increasing fluorination in a series of carbazole-based nanoporous organic polymers (CNOPs) for C₂H₂/CO₂ separation. Contrary to common expectations, the C₂H₂/CO₂ selectivity progressively decreases with higher fluorine content. Detailed characterizations show that this reduction in performance arises from a synergistic combination of structural deterioration and adverse electronic effects. Specifically, porosity analysis indicates a substantial collapse in micropore volume (∼25%), attributed to sterically induced inefficient chain packing. More critically, direct experimental evidence from isosteric heat of adsorption (Q_st) shows a significant decrease in C₂H₂ binding affinity (from ∼26.7 kJ·mol^-1 to ∼25.3 kJ·mol^-1). This study demonstrates that substantial structural degradation and electronic depletion can negate the anticipated benefits of fluorination. These findings provide critical guidelines for the targeted design of advanced separation materials.