Nat. Commun. 8, 1599 (2017)

Credit: Macmillan Publishers Ltd

Researchers have synthesized various porous organic networks (PONs) with high surface area in liquid phase and demonstrated their capability in heterogeneous catalysis, gas capture and storage, energy storage and optoelectronics. However, no PONs have been obtained via solid-state reactions. Now, Jong-Beom Baek and colleagues from Ulsan National Institute of Science and Technology report the formation of a 3D PON via solid-state explosion of organic single crystals.

The key building block of the PON, 2,3,6,7,14,15-hexaethynyl-9,10-dihydro-9,10-[1,2]benzenoanthracene (HEA), contains three enediyne groups, enabling it to self-polymerize via the Bergman reaction (cycloaromatization) to produce a 3D polyHEA. However, the occurrence of this reaction normally requires the presence of hydrogen donors in liquid phase, along with dicobalt octacarbonyl catalysts. Now, Baek et al. demonstrate that the HEA single crystals, consisting of HEA, two acetone molecules and one water molecule, can form a 3D PON in 0.11 s via an explosive solid-state reaction when the bulk crystals are heated with a heating gun. Recognizing the dominating effect of the primer molecules (acetone and water), they propose that these molecules can accumulate kinetic energy when heat is applied. Upon their sudden evacuation, the crystal lattices are disturbed and the enediyne groups become closer together, resulting in the formation of polyHEA via cycloaromatization. The synthesized polyHEA shows fish-net-type morphology and high thermal stability in air. Moreover, it exhibits distinguished CO2 adsorption capability due to the abundant electron-rich cavities.