Porous Organic Salts Composed of Terphenyl Sulfonic Acid and Their Bottleneck Designability

Porous organic salts (POSs) are constructed through a strong charge-assisted hydrogen bond between sulfonic and amino groups. The molecular design of sulfonic acid, the linker part, enables various porous structures. In the current work, we synthesized p-terphenyl-4,4’’-disulfonic acid (TPDS), whose molecular structure can be easily modified by organic synthesis. Combining of TPDS and bulky tri-p-tolylmethanamine (TPMA-Me), which has three methyl groups at each para-position of the phenyl groups of triphenylmethylamine (TPMA), gave POS with one-dimensional pore channels having two different types of bottlenecks. The central benzene ring of TPDS is exposed on the surface of the pore. Therefore, we combined 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzenesulfonic acid (BTDBS) containing 2,1,3-benzothiadiazole (BT) with TPMA-Me, and successfully constructed a one-dimensional pore channel with a bottleneck of 3.5 Å, by exposing BT to the surface of the pore. BTDBS/TPMA-Me exhibited a large adsorption/desorption hysteresis of nitrogen because of the bottleneck, electronic state of BT, and larger oxygen adsorption than the isostructural TPDS/TPMA-Me. Systematic and intended modulation of the pore structure of POS based on the modification of sulfonic acid was demonstrated, and for the first time, we established a precise design methodology for a one-dimensional pore channel with a bottleneck and high crystallinity in metal-free porous organic materials.