An approach to transforming amorphous organic networks into crystalline covalent organic frameworks (COFs) with retention of the colloidal nanosize and uniform morphology is presented. Specifically,F e 3 O 4 nanoclusters are encapsulated by ad isordering polyimine network via the Schiff-base reaction. The formed imine bonds could be reconstructed under thermodynamic control to reform the polyimine networks into imine-linked COFs in situ. Suchacore-shell microsphere exhibits the uniform sizea nd spherical shape, controllable COF shell thickness,a ccessible surface modification, and improved solution dispersibility as well as maintenance of high surface area, periodic micropores,and superior magnetic responsiveness.A dditionally,t he photothermal conversion effect is demonstrated for the first time on the nanoCOF layers upon exposure to near infrared light, providing convincing evidence for potential use in phototherapy.Covalent organic frameworks (COFs) are two-or threedimensional crystalline porous polymers that originate from the topological polymerization of building blocks with predesigned geometry and symmetry by virtue of dynamic covalent bonds (e.g.i mine, [1] enamine, [2] hydrazine, [3] azine, [4] b-ketoenamine, [5] and boronate ester [6] ). This emerging family presents high and regular porosity,tunable pore size and pore wall chemistry,a nd structural predictability and stability. [7] These characteristics endow COFs with outstanding performances for aw ide-range of applications,s uch as gas storage, [8] heterogeneous catalysis, [9] luminescence, [10] optical sensing, [11] proton conduction, [12] and photoconduction. [13] Against this backdrop,t here has been significant interest very recently in the miniaturization of COFs to the nanometer scale, [14] for the sake of extending the applicability and enhancing the proper-ties of COFs.I ndeed, the nanoCOFs can overcome,t os ome extent, the poor solution properties of the corresponding bulk materials,and they have been developed into nanocarriers for biomedical applications,such as drug delivery [15] and enzyme immobilization. [14b] However,most of the materials described were not very compatible with biomedical and pharmaceutical applications,a nd, with few exceptions,t hey were not engineered as dispersible nanoparticles to enable in vivo circulation by intravenous administration. As far as is known, the COF assemblies are prepared with no way of controlling size and morphology under solvothermal conditions.
