Recent progress in covalent organic frameworks as light-emitting materials

As an emerging class of crystalline materials, covalent organic frameworks (COFs) have drawn numerous attentions owing to their light weight and highly ordered porous structure. Compared with one-dimensional conjugated polymers, conjugated COFs are able to extend the conjugation in two- or even three-dimensional directions, which endows them as promising candidates of light-emitting materials. In this review, the recent progress in photoluminescent COFs will be discussed from the mechanisms to the proposed design strategies and finally to the corresponding applications. Most recent developments (especially from 2019 to now) will be highlighted. Moreover, the summary and perspective of COFs as light-emitting materials will be presented, aiming to provide some guidelines for the development of luminescent COFs.