Polymer-Driven Self-Templated Synthesis of Boronate-COF Hollow Spheres: Toward the Development of Size-Selective Nanoreactors.

Covalent organic frameworks are a family of porous crystalline structures gaining attention due to their promising applications. However, despite significant efforts, the synthesis and understanding of uniform and specific morphologies remain a challenge. Herein, we report the first self-templated synthesis of hollow spherical boronate ester-linked COFs-polymers. A time-dependent investigation reveals the formation of hollow spheres driven by an inside-out Ostwald ripening mechanism, exclusively for COF-10 in the presence of a catechol-poly(N-isopropylacrylamide) (catechol-PNIPAm) polymer. The synthesized hollow spheres show a hydrodynamic radius of 300 nm, an oriented crystallinity, and continuous hexagonal pore channels throughout the membrane, associated with a high surface area (~800 m2·g-1). Interestingly, the hollow sphere cavity enables the encapsulation of a fluorogenic, thiol-responsive dye while the porous membrane regulates the size-selective penetration of thiols. Only thiols of appropriate size can access the encapsulated dye, thereby triggering fluorescence restoration.