Additive Mixing of Emissive Ligands in Covalent Organic Frameworks for White Light Emission.

Emissive covalent organic frameworks (COFs) are a promising class of crystalline materials that have demonstrated applications for sensing and light-emitting diodes. However, white light emission from a single COF has not been achieved yet as it requires multicomponent organic chromophores that simultaneously emit blue, green, and red light. In this work, we report the successful synthesis of a single COF with efficient white light emission by utilizing tunable emission properties of 2,1,3-benzothiadazole after incorporating different functional groups on its core structure, which results in the formation of three ligands, i.e., 4',4-(benzothiadiazole-4,7-diyl)-dibenzaldehyde (BTD), 4,4'-(benzoselenadiazole-4,7-diyl)-dibenzaldehyde (BSD), and 4,4'-(naphtho[2,3- c ][1,2,3] selenadiazole-4,9-diyl)-dibenzaldehyde (NSD), that emit in the blue, green, and red regions of the visible light spectrum. We show that white light emission can only occur when BTD, BSD, and NSD are assembled in a single COF structure due to the facilitated energy transfer process from BTD to BSD/NSD. This work demonstrates a unique approach to developing new white light-emitting materials based on the COF structure.