Three-Dimensional Nonconjugated Microporous Organic Polymers Based on Tröger's Base: Integrating Physical Confinement and Chemisorption for Enhanced NOx Capture.

Nitrogen oxides (NOx) demand urgent capture-they can trigger self-catalytic decomposition in nitrocellulose, risking combustion or explosion under high temperature and humidity. To counteract this, rigid, nonplanar building blocks with aliphatic C-H units, contorted Tröger's base (TB) units, are integrated into microporous organic polymers (MOPs), where micropores enable rapid physisorption, tertiary nitrogen sites allow stable chemisorption, and the aliphatic C-H units within these scaffolds restrict conjugation and donate electrons to benzene rings, further promoting continuous NOx adsorption. Among the polymers, triptycene-based TB (Trip-TB, 1011 m2 g-1, 3.36 mmol g-1) and tetraphenyladamantane-based TB (TAPA-TB, 826 m2 g-1, 3.32 mmol g-1) outperform the triphenylbenzene analog (TAPB-TB, 926 m2 g-1, 2.99 mmol g-1). With only 3 wt% Trip-TB, NOx release is reduced by 70.2 % in titration tests, and the methyl violet color-change time extends 3.15-fold. This enhancement is attributed to the conjugation-interrupting and electron-donating effects of the aliphatic cores to the benzene rings. Characterization and calculations further elucidate the adsorption mechanism. Collectively, these findings establish a cooperative physicochemical mechanism for efficient NOx capture and provide a rational blueprint for adsorbent design.