Fluorescent Covalent Organic Frameworks: A Promising Material Platform for Explosive Sensing

Yuhang Qian; Jiani Li; Mingyang Ji; Jundan Li; Dongge Ma; Anan Liu; Yubao Zhao; Chun Yang

doi:10.3389/fchem.2022.943813

Fluorescent Covalent Organic Frameworks: A Promising Material Platform for Explosive Sensing

Front Chem. 2022 Jul 15:10:943813. doi: 10.3389/fchem.2022.943813. eCollection 2022.

Authors

Yuhang Qian¹, Jiani Li¹, Mingyang Ji¹, Jundan Li¹, Dongge Ma¹, Anan Liu², Yubao Zhao³, Chun Yang⁴

Affiliations

¹ College of Chemistry and Materials Engineering, Beijing Technology and Business University, Beijing, China.
² Basic Experimental Centre for Natural Science, University of Science and Technology Beijing, Beijing, China.
³ Institute of Environmental Research at Greater Bay, Guangzhou University, Guangzhou, China.
⁴ College of Life Sciences and Chemistry, Hunan University of Technology, Zhuzhou, China.

Abstract

Covalent organic frameworks (COFs) are a novel class of porous crystalline organic materials with organic small molecule units connected by strong covalent bonds and extending in two- or three-dimension in an ordered mode. The tunability, porosity, and crystallinity have endowed covalent organic frameworks the capability of multi-faceted functionality. Introduction of fluorophores into their backbones or side-chains creates emissive covalent organic frameworks. Compared with common fluorescent organic solid materials, COFs possess several intrinsic advantages being as a type of irreplaceable fluorescence materials mainly because its highly developed pore structures can accommodate various types of guest analytes by specific or non-specific chemical bonding and non-bonding interaction. Developments in fluorescent COFs have provided opportunities to enhance sensing performance. Moreover, due to its inherent rigidified structures and fixed conformations, the intramolecular rotation, vibration, and motion occurred in common organic small molecules, and organic solid systems can be greatly inhibited. This inhibition decreases the decay of excited-state energy as heat and blocks the non-radiative quenching channel. Thus, fluorescent COFs can be designed, synthesized, and precisely tuned to exhibit optimal luminescence properties in comparison with common homogeneous dissolved organic small molecule dyes and can even compete with the currently mainstream organic solid semiconductor-based luminescence materials. This mini-review discusses the major design principle and the state-of-the-art paragon examples of fluorescent COFs and their typical applications in the detection and monitoring of some key explosive chemicals by fluorescence analysis. The challenges and the future direction of fluorescent COFs are also covered in detail in the concluding section.

Keywords: chemical sensing; covalent organic frameworks; explosive sensing; fluorescence; fluorescence mechanisms.

Publication types

Review