Solid-State Photoluminescent Imine-Linked Two-Dimensional Covalent Organic Frameworks

The development of efficient solid-state luminescent covalent organic frameworks (COFs) is crucial for advancing applications in sensing, imaging, and optoelectronics. However, achieving high photoluminescent quantum yields (PLQY) in imine-linked COFs remains challenging due to the presence of complex nonradiative quenching pathways. Here, the design and synthesis of a novel series of solid-state photoluminescent imine-linked 2D covalent organic frameworks (2D COFs) are reported through condensation of rigid building blocks. These COFs display high crystallinity and porosity, and with a remarkable PLQY of up to 39% in the solid state. The high luminescent efficiency is attributed to the donor-acceptor-donor structure within the aldehyde moieties, which facilitates selective charge transfer excitation between the donor moiety, triphenylamine, and the acceptor moiety, benzothiadiazole, bypassing the imine bonds, suppressing nonradiative quenching pathways associated with imine bond rotation in the excited states. Furthermore, the obtained COF shows potential for bioimaging applications.