Targeted synthesis of porous aromatic frameworks with stimuli-responsive adsorption properties

Abstract

Two porous aromatic frameworks, PAF-36 and PAF-37, containing azo moieties, were synthesized via Sonogashira-Hagihara coupling reactions. Gas sorption measurements indicated that reversible stimuli-responsive adsorption properties were triggered by ultraviolet (UV) irradiation and heat treatment, because of the presence of azo functional groups. The initial Brunauer-Emmett-Teller (BET) surface areas of PAF-36 and PAF-37 were 325 and 443 m(2) g(-1), respectively. After UV irradiation, the BET surface areas increased during the trans-cis isomerization process, and the micropore sizes, around 6 and 8 angstrom, also increased. In addition, the CO2 adsorption capacities increased slightly because of trans-cis conversion of azo groups. It is worth mentioning that the CO2 uptakes of the polymers were almost constant during multiple cycles of alternating external stimuli, displaying high switchability of the trans-cis isomerization.