Optoelectronic processes in covalent organic frameworks

Covalent organic frameworks (COFs) are crystalline porous materials constructed from molecular building blocks using diverse linkage chemistries. Their modular construction system allows not only for tailor-made design but also for an immense variety of building blocks, opening the door to numerous different functionalities and potential applications. As a consequence, a large number of building blocks that can act as light-harvesters, semiconductors, ligands, binding sites or redox centers have recently been integrated into the scaffolds of COFs. This unique combination of reticular chemistry with the molecular control of intrinsic properties paves the way towards the design of new semiconducting materials for (opto-)electronic applications such as sensors, photocatalysts or -electrodes, supercapacitor and battery materials, solar-harvesting devices or light emitting diodes. With new developments regarding the linkage motif, highly stable but still tunable COFs have been developed for applications even under harsh conditions. Further, the molecular stacking modes and distances in the COFs have been investigated as a powerful means to control optical and electrical characteristics of these self-assembled frameworks. Advanced understanding of optoelectronic processes in COFs has enabled their implementation in optoelectronic devices with promising potential for real-world applications. This review highlights the key developments of design concepts for the synthesis of electro- and photoactive COFs as well as our understanding of optoelectronic processes in these frameworks, hence establishing a new paradigm for the rational construction of well-defined novel optoelectronic materials and devices.