Manipulation of Amorphous‐to‐Crystalline Transformation: Towards the Construction of Covalent Organic Framework Hybrid Microspheres with NIR Photothermal Conversion Ability

Abstract

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, Fe O nanoclusters are encapsulated by a disordering 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. Such a core-shell microsphere exhibits the uniform size and spherical shape, controllable COF shell thickness, accessible surface modification, and improved solution dispersibility as well as maintenance of high surface area, periodic micropores, and superior magnetic responsiveness. Additionally, the 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 as a Platform for Multidimensional Polymerization

“…Besides direct synthesis, COF colloids can also be formed on a template to make hybrid core–shell structures, as demonstrated by Guo and co-workers, who formed COF-coated Fe 3 O 4 nanoparticles (Figure 9B,C) enabling them to be manipulated by magnetic fields (Figure 9D). 90 …”

“…(B) The formation of an imine COF shell on an Fe 3 O 4 nanoparticle and demonstrations of the hybrid’s Tyndall effect and magnetism (C, D). Adapted with permission from ref (90). Copyright 2016 John Wiley & Sons, Inc.…”

A Novel Strategy for the Construction of Covalent Organic Frameworks from Nonporous Covalent Organic Polymers

“…First, the replacement of the dynamic imine bond occurs at the outer surface of COP-1 to generate an amorphous phase due to the nonporous and dense nature of COP-1. Thef inal step is the defect correction of COF-1 to afford highly crystalline materials.T he transformation process of COP-1 to COF-1 differs greatly from the reconstruction of COFs based on dynamic bonds and the devitrification of amorphous polyamide network polymers based on irreversible amide bond, [13] in which adjusting the local placement and switching the direction of the bond extension of the building blocks would transform the amorphous phase to ahighly crystalline phase in principle.For the COP-1 to COF-1t ransformation, al ong-range shift and exchange of the linkers is necessary,a nd thus the new linker diffuses in, the linker is replaced, and the original linker leaves. [10,16] In the second step of the COP-to-COF transformation, more and more fragments start to assemble into ordered architectures to form COF-1.…”

“…[11] Yaghi and coworkers explored the COF-to-COF conversion method by linker substitution, cyclization, and oxidation. We hypothesized whether it may be possible to construct highly crystalline and porous COFs from amorphous nonporous covalent organic polymers (COPs), while this possibility is usually overlooked in the preparation of COFs.I ti s worth pointing out that this method to construct COFs is different from previous reports on error-correction [12] or reconstruction [13] of COFs. We hypothesized whether it may be possible to construct highly crystalline and porous COFs from amorphous nonporous covalent organic polymers (COPs), while this possibility is usually overlooked in the preparation of COFs.I ti s worth pointing out that this method to construct COFs is different from previous reports on error-correction [12] or reconstruction [13] of COFs.…”

Aptamer‐Functionalized Magnetic Conjugated Organic Framework for Selective Extraction of Traces of Hydroxylated Polychlorinated Biphenyls in Human Serum

“…Moreover,c omparedw ith the spectrum of Fe 3 O 4 -15, the diffractionp eak that appeared ata bout 2.38 in that of Fe 3 O 4 @COF-Apt-15 might be due to the crystallinity of the COF shell. [40] Figure 5D shows the thermogravimetric analysis/derivative thermogravimetric (TGA/DTG) curveso fF e 3 O 4 -15 and Fe 3 O 4 @COF-Apt-15 from 20 to 800 8Cw ith ar amp rate of 10 8Cmin À1 .A ss hown in Figure 5D ( [41] Verification of extraction selectivity The magnetic properties of Fe 3 O 4 -15 and Fe 3 O 4 @COF-Apt-15 were determined by vibrating-sample magnetometry (VSM).…”