Multivariate Synthetic Strategy for Improving Crystallinity of Zwitterionic Squaraine‐Linked Covalent Organic Frameworks with Enhanced Photothermal Performance

Abstract

Two‐dimensional covalent organic frameworks (2D COFs) offer a designable platform to explore porous polyelectrolyte frameworks with periodic ionic skeletons and uniform pore channels. However, the crystallinity of ionized 2D COF is often far from satisfactory as the electrostatic assembly of structures impedes the ordered layered arrangement. Here, a multivariate synthetic strategy to synthesize a highly crystalline squaraine (SQ)‐linked zwitterionic 2D COF is proved. A neutral aldehyde monomer copolymerizes with squaric acid (SA) and amines in a controlled manner, resulting in the ionized COF with linkage heterogeneity in one tetragonal framework. Thus, the zwitterions of SQ are spatially isolated to minimize the electrostatic interaction and maintain the highly ordered layered stacking. With the addition of 85%–90% SA (relative to a total of aldehydes and SA), a fully SQ‐linked zwitterionic 2D COF is achieved by the in‐situ conversion of imine to SQ linkages. Such a highly crystalline SQ‐linked COF promotes absorptivity in a full spectrum and photothermal conversion performances, and in turn, it exhibits enhanced solar‐to‐vapor generation with an efficiency of as high as 92.19%. These results suggest that synthetically regulating charge distribution is desirable to constitute a family of new crystalline polyelectrolyte frameworks.

Emerging Materials for Interfacial Solar‐Driven Water Purification

“…Ding et al synthesized a squaraine (SQ)-linked COF as solar absorber, which also showed broad absorption from 400 to 2400 nm (Figure 5b). [32] Applying melamine foam (MF) as substrates, the SQ-COF/MF evaporator could generate vapor at 1.35 kg m À 2 h À 1 under one sun. Huang et al incorporated diketopyrrolopyrrole (DPP) into a COF backbone, which again yielded broad light absorption (Figure 5c).…”

“…Applying monomers containing specific dye molecules is an effective approach to extend the light absorption. [32,40,41] Since 1,4,5,8-Tetrakis(phenylamino)anthracene-9,10-dione (TPAD) is known as a NIR dye, Yan et al utilized amine-functionalized TPAD as building units to synthesize a TPAD-COF (Figure 5a). [40] TPAD-COF showed a broad light absorption covering the entire UV/Vis and NIR regions as well as superhydrophilicity.…”

“…Our group recently developed free-standing COF/graphene dual-region hydrogels (CGHs) as solar evaporators by a one-step hydrothermal process. [18b] Applying 1,3,5-triformylphloroglucinol and 2,5-diaminobenzenesulfonic acid as monomers, TpPa-SO 3 H-COF with [40] b) SQ-linked COF, [32] and c) DPP-COF. [41] d) Chemical structure of TpPa-SO 3 H. e) Photograph of CGH-50 synthesized using 20 mL (left) and 120 mL (right) autoclaves, respectively.…”

Covalent Organic Frameworks with Ionic Liquid-Moieties (ILCOFs): Structures, Synthesis, and CO2 Conversion

“…Recently, Fan and Zhang et al [ 70 ] reported two photoactive SQ-linked COFs (SQ-COF-1 and SQ-COF-2), prepared through the condensation of SA with TAPB or tris(4-aminophenyl)amine (TAA). Guo et al [ 71 ] investigated the multivariate synthesis of SQ-linked COFs, Py-TPA 1-X -SQ X (X = [SA]/([TPA] + [SA])), by the reaction of 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayl) tetraaniline (TAPPy) with terephthalaldehyde (TPA) and SA. TPA was a neutral structural stabilizer.…”

Ion‐in‐Conjugation: A Promising Concept for Multifunctional Organic Semiconductors

“…[154] Guo et al designed a multivariate synthetic strategy to synthesize a squaraine-COF with improved crystallinity, high charge density, and exceptional chemical stability for enhanced photothermal conversion performance upon exposure to an 808 nm laser and simulated sunlight (1 kW m −2 ). [155]…”