Highly Flexible Porous Aromatic Frameworks with Exceptional Adsorption Capacity Toward Volatile Organic Compounds

In this work we report a novel strategy to enhance the adsorption capacity of conventional porous materials by engineering intrinsic framework flexibility into porous aromatic frameworks (PAFs). Through Yamamoto-type copolymerization of a rigid tetrahedral monomer (tetrakis(4-bromophenyl)methane) and a flexible counterpart (tetrakis[(4-bromophenoxy)methyl]methane), we synthesized a series of flexible PAFs (FPAF-x, x = 0-2) with tunable flexibility. FPAF-0.5 with moderate flexibility and surface area (854 m² g^-1) achieves exceptionally high volatile organic compound (VOC) adsorption capacities for various VOCs (e.g., 410.7 wt% for THF and 339.4 wt% for 3-methylthiophene), outperforming many other porous materials reported to date. Both thermodynamic equilibrium and dynamics VOC vapor adsorption studies reveal that optimal flexibility enables guest-adaptive structural transformation, allowing pore expansion to accommodate additional VOC molecules after initial pore filling. Moreover, polar and aromatic VOCs induce greater framework expansion than nonpolar analogues, which can also enhance the VOC uptake capacity in FPAFs. This work establishes flexibility engineering as a design principle for next-generation adsorbents, improving the efficiency of VOC adsorption.