Copolymerization of terephthalaldehyde with pyrrole, indole and carbazole gives microporous POFs functionalized with unpaired electrons

Abstract

A new family of paramagnetic microporous polymeric organic frameworks (POFs) has been developed through the co-polymerization of terephthalaldehyde and pyrrole, indole, and carbazole, respectively. These POFs are functionalized with stable unpaired electrons and electron paramagnetic resonance spectroscopy and pulsed ENDOR spectroscopy confirms their existence. The free radicals are produced in the early steps of polymerization and are responsible for their optical properties and the chemical adsorption properties of the POFs. The optical band gap of these materials ranges from 0.8 to 1.6 eV. The new POFs have spherical morphology and exhibit surface areas up to 777 m² g⁻¹ (Pyr-POF-1). Furthermore, Pyr-POF-1 displays the uptake of CO₂ 14% wt and C₂H₆ 9% wt at 273 K/1 bar and H₂ 1.2% wt at 77 K/1 bar. The pyrrole based material (Pyr-POF-2) shows high capacity for CO₂, 10% wt, under ambient conditions (298 K/1 bar) and the isosteric heat of CO₂ adsorption of ∼34 kJ mol⁻¹. The preparation of this new POF family is based on a very simple synthetic pathway and highlights the significance of terephthalaldehyde as a precursor for the synthesis of low cost functional porous polymers.