A metal-free approach to bipyridinium salt-based conjugated porous polymers with olefin linkages

Abstract

Conjugated porous polymers are emerging as a new class of polymeric materials with substantial unique properties. Although versatile synthetic strategies have been developed, the search for a sustainable and reliable approach is still extremely desirable for achieving new polymeric species according to the demands for environmental benignity and biocompatibility. Here, we present the synthesis of a new family of olefin-linked conjugated porous polymers by the Knoevenagel condensation of a key monomer 1,1′,6,6′-tetramethyl-[3,3′-bipyridine]-1,1′-diium iodide (TMBPI) with different aryl aldehyde derivatives. In such a strategy, the methyl groups of pyridinium moieties were facile to be activated under organic base catalysis without any metal additives, and they subsequently undergo nucleophilic addition to form aldehyde groups. The resulting carbon–carbon double bond-linked porous polymers feature π-extended rigid networks, ultra-high chemical stability, and high surface areas with micro-/meso-channels, which were completely revealed by optical spectra, solid-state ¹³C NMR, FT-IR, thermogravimetry, XPS and nitrogen adsorption/desorption analyses. In addition, the unique highly charged skeletons of the as-prepared porous polymers make them well dispersed in some polar solvents, showing large zeta potentials (up to ζ = 16 ± 2.8 mV). Accordingly, such cationic porous polymers enable impeding bacterial growth, exhibiting good antibacterial properties against Gram-negative bacteria (e.g. E. coli).