Visible-Light-Responsive Crystalline Solids by Equipping Covalent Organic Frameworks with Donor-Acceptor Stenhouse Adducts

Abstract

Controlling properties of crystalline solids by light remains a challenge because the lack of intrinsic structural flexibility limits the necessary molecular mobility for photoisomerization. In this work, we reported a series of visible-light-responsive covalent organic frameworks (COFs) by introducing donor-acceptor Stenhouse adducts (DASAs) with various electron-withdrawing moieties via a post-modified strategy. The DASAs-functionalized COFs exhibit distorted honeycomb layered topology with long-range periodicity. The DASAs grafted on the skeletons are pointing into the nanopores of COFs, which weakens intermolecular aggregation and ensures sufficient free volume to undergo reversible isomerization between linear and cyclic states. Furthermore, the crystalline and optical properties of COFs as well as the geometrical size and hydrophilicity inside the nanopores were reversibly controlled by alternating visible light irradiation and heat. Finally, methyl violet was used as the cargo molecules to be immobilized into the nanopores of COFs, which showed fast release under controlling of visible light. (Figure presented.).