Crystallinity and stability of covalent organic frameworks
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tps://doi.org/10.1007/s11426-020-9836-x
SPECIAL ISSUE: 2020 Emerging Investigator Issue
Crystallinity and stability of covalent organic frameworks †
†
Xin Huang , Chao Sun & Xiao Feng
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Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China Received June 8, 2020; accepted July 20, 2020; published online September 2, 2020
Covalent organic frameworks (COFs) are a class of organic porous polymers with high crystallinity, and their structures can be precisely tailored via topology design. Owing to the characteristics of permanent pores, periodic structures and rich building blocks, COFs have triggered tremendous attention in the past fifteen years and are extensively investigated in various fields. Crystallinity and stability are two crucial features for practical applications. In general, these two features are contradictory for COFs formed via dynamic covalent chemistry (DCC). High thermodynamic reversibility is usually required to attain exceptional crystallinity of COFs, often resulting in limited stability. The first two reported COFs are based on the boroxine and boronate ester linkages, which are unstable in water and even in humid conditions. Therefore, many researchers doubt the stability of COFs for real applications. Actually, in these years, various novel linkages have been developed for the construction of COFs, and numerous newly synthesized COFs are robust towards strong acid/base and even some of them can resist the attack of strong oxidizing and reducing agents. In this review, we focus on the linkage chemistry of the COFs in terms of crystallinity and stability, further extending it to the investigation in the mechanisms of the crystal growth and the overall regulation of the contradiction between stability and crystallinity. The strategies for improving the crystallinity, including selecting building units, introducing non-covalent interactions and slowing nucleation and growth rate, are described in the third section, while the methodologies for increasing the stability from the viewpoints of chemical modification and non-covalent interactions are summarized in the fourth section. Finally, the challenges and perspectives are presented. covalent organic frameworks, crystallinity, stability, dynamic covalent chemistry, linkage chemistry Citation:
Huang X, Sun C, Feng X. Crystallinity and stability of covalent organic frameworks. Sci China Chem, 2020, 63, https://doi.org/10.1007/s11426-0209836-x
1 Introduction Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers connected by organic building units through covalent bonds [1–6]. Since the pioneering work reported by Côté and Yaghi et al. [7] on COF-1 and COF-5 in 2005, the advent of COFs has significantly enriched the research of porous materials. In the past fifteen years, hundreds of COFs have been successfully synthesized through t
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