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Insights Into Structural Features of Azo-bridged Porous Organic Polymers by Using Solid-state NMR Spectroscopy

Emissions of carbon dioxide (CO2) into our environment are a huge problem due to the impact on climate changes, especially because there are not yet effective solutions to permanently capture and store CO2. Porous organic polymers (POPs) are good candidates for CO2 capture and separation because of their large specific surface area, high porosity, high chemical and thermal stability and low density. It has recently been found that incorporation of nitrogen-rich units, such as azo, improves the interaction between POPs and CO2 molecules and enhances CO2/N2 selectivity. Herein, we synthesized a series of new azo-bridged POPs by reductive homocoupling of aromatic trinitro derivative, and by condensation reactions of aromatic trinitro derivative and various aromatic diamino compounds which differ in length and rigidity. The obtained POPs were found to be insoluble amorphous solids of very high termal stability. IR spectra showed the bands of low intensity which could be attributed to the stretching vibration of new azo bonds. In order to confirm the formation of azo linkages and the possible presence of unreacted terminal groups, 13C CP/MAS NMR spectra of polymeric products and starting compounds were acquired and compared. Careful inspection of collected 13C CP/MAS NMR spectra indicated the formation of new azo bonds and the presence of unreacted amino groups in final polymeric materials.

Porous organic polymers, aromatic trinitro compound, aromatic diamino compounds, solid-state NMR spectroscopy

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