Electron-deficient two-dimensional poly(arylene vinylene) covalent organic frameworks: efficient synthesis and host-guest interaction

Crystalline and porous 2D poly(arylene vinylene)s (2D PAVs), i.e. vinylene-linked 2D conjugated covalent organic frameworks, represent promising materials for electronic and electrochemical applications. Chemically robust 2D PAVs with strong electron affinity are highly desirable for effective host–guest charge transfer to achieve enhanced device performance. Herein, we report the efficient synthesis and host–guest interaction of two novel 2D PAVs incorporating electron-deficient bipyrazine units with a N-free 2D PAV as a reference. They are crystalline and chemically robust. Various spectroscopies coupled with theoretical calculations indicate that the abundant N sites boost the electron affinity of 2D PAVs. We test their efficiency in hosting guest sulfur species and find that the electron-deficient materials help to physically confine and stabilize sulfur/polysulfide (e.g., Li2S6) molecules with facilitated intermolecular charge transfer in the porous channels. As a result, using sulfur encapsulated by 2D PAVs as electrode materials, we achieve high specific capacities with excellent capacity retention after 200 charge–discharge cycles for Li–sulfur batteries.