Synergistic experimental and computational investigation of azo-linked porphyrin-based porous organic polymers for CO2 capture†

We synthesized a series of azo-linked porphyrin-based porous organic polymers (APPs) with linear, bent, and trigonal linkers (APP-1 to APP-6) and with directly connected tetraphenylporphyrin units (APP-7a, APP-7b and APP-8). The synthesized APPs are amorphous solids demonstrating good thermal stability and diverse BET surface areas. APPs with linkers showed significantly higher surface areas (469 to 608 m² g⁻¹) compared to those with directly connected tetraphenylporphyrin units (0.3 to 23 m² g⁻¹). Higher surface areas correlated with enhanced CO₂ adsorption, particularly for APP-1, APP-2, and APP-5 with experimental CO₂ uptake values of 41 mg g⁻¹, 38 mg g⁻¹, and 38 mg g⁻¹, respectively, at 306 K. The computational study supported the experimental findings and provided insights on how surface area and the local landscape affect the CO₂ adsorption. Although the computational models were based on ideal structures, while the experiments revealed the materials were amorphous, the calculated CO₂ adsorption capacities were roughly comparable to the experimental results, particularly for the 3D systems (APP-5 and APP-6) and the 2D systems with directly connected building units (APP-7 and APP-8). Porphyrin units in the framework serve as additional binding sites for CO₂, especially when unhindered and available on either side of the porphyrin plane. This work highlights the potential of 2D layered APPs and 3D topologies for efficient CO₂ capture.