For most of the history of chemistry, polymeric materials were strictly known as 1D, monomers strung together in a linear fashion to form long chains. Recently, new methods and monomers were developed that allow the growth of two-dimensional graphene-like polymeric structures, known as 2D polymers (2DPs). Due to their 2D nature, these polymers are naturally highly ordered, gaining novel applications as nanoporous membranes for use in separating specific molecules (CO₂ capturing, for example), in batteries (as anionic conductors), as extremely high surface area catalyst supports, ultrathin coatings and many more. However, the current array of 2D monomers is very narrow, as few molecules fit the packing and symmetry criteria required for these materials. One such class are 3-fold star-shaped styryl-pyrylium salts. These monomers present excellent crystal packing for topochemical polymerization via π-π stacking. At the same time, the pyrylium ring facilitates exfoliation via charge repulsion and provides an easy post-polymerization modification route via its high reactivity towards nucleophiles. Previously, such a monomer was obtained with bulky t-butyl groups close to the reactive site of the pyrylium ring^[1], severely limiting the options for modification due to steric bulk. We report a new monomer with isopropyl groups that can be used to obtain, for example, N-alkyl-pyrydinium containing 2DPs, which have proven to be excellent anionic conductors in batteries, having been reported to enable capacity retention of 93% after 1000 cycles^[2]. This monomer proves vastly pluripotent in its functionalization, amine groups can be inserted for CO₂ capture or even bulky substituents for adjustable pore size. The compound has proven easy and relatively inexpensive to make on a large scale, while its crystals can be grown to relatively large sizes from common solvents.

[1]        R. Z. Lange, G. Hofer, T. Weber, A. Dieter Schlüter, Journal of the American Chemical Society, 2017, 139 (5), 2053-2059

[2]        D. Sabaghi, Z. Wang, P. Bhauriyal et al., Nature Communications, 2023, 14, 760