Tuneable near white-emissive two-dimensional covalent organic frameworks

• Published in: Nature communications Vol. 9; no. 1; pp. 2335 - 9
• Main Authors: Li, Xing, Gao, Qiang, Wang, Juefan, Chen, Yifeng, Chen, Zhi-Hui, Xu, Hai-Sen, Tang, Wei, Leng, Kai, Ning, Guo-Hong, Wu, Jishan, Xu, Qing-Hua, Quek, Su Ying, Lu, Yixin, Loh, Kian Ping
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13.06.2018; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 140/131; 140/58; 147/135; 147/143; 639/301/357/537; 639/301/923/3931; 639/638/455/960; Chemical bonds; Emissivity; Emitters; Energy dissipation; Fluorescence; Humanities and Social Sciences; Hydrogen bonding; Hydrogen bonds; Interlayers; multidisciplinary; Photoluminescence; Photons; Rotation; Science; Science (multidisciplinary); Solid state; Stacking; Thermal energy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-04769-6

Most two-dimensional (2D) covalent organic frameworks (COFs) are non-fluorescent in the solid state even when they are constructed from emissive building blocks. The fluorescence quenching is usually attributed to non-irradiative rotation-related or π–π stacking-caused thermal energy dissipation process. Currently there is a lack of guiding principle on how to design fluorescent, solid-state material made of COF. Herein, we demonstrate that the eclipsed stacking structure of 2D COFs can be used to turn on, and tune, the solid-state photoluminescence from non-emissive building blocks by the restriction of intramolecular bond rotation via intralayer and interlayer hydrogen bonds among highly organized layers in the eclipse-stacked COFs. Our COFs serve as a platform whereby the size of the conjugated linkers and side-chain functionalities can be varied, rendering the emission colour-tuneable from blue to yellow and even white. This work provides a guide to design new solid-state emitters using COFs. Encoding functionalities in covalent organic frameworks (COFs) is important for widening their application field but the development of fluorescent COFs is hampered by a lack of guiding design principles. Here the authors demonstrate tuning and switching of the photoluminescence in 2D COFs made of non-emissive building blocks.