Boosting Covalent Organic Framework Luminescence by Suppressing Nonradiative Pathways†

Abstract

The construction of luminescent two-dimensional (2D) imine-linked covalent organic frameworks (COFs) is a formidable challenge due to the strong interlayer stacking and bond rotations that typically suppress intramolecular charge transfer (ICT), leading to nonradiative energy dissipation. Herein, three COFs with tailored interlayer distances and bond rotations are designed to modulate the ICT behaviours. The targeted COF (TPAZ-TPE-COF) achieved a significantly enhanced photoluminescence quantum yield (PLQY) of 21.22% in the solid state by restricting bond rotation and enlarging the layer distance. This represents a 3.5-fold and 530.5-fold improvement over TPAZ-PYTA-COF (6.15%), which has a shortened interlayer space, and TPAZ-PATA-COF (0.04%), which exhibits strong bond rotations, respectively. Importantly, TPAZ-TPE-COF also exhibits exceptional sensing performance for iron ions, with a detection limit at the ppb level. Both experimental and theoretical analyses reveal that the prominent luminescent performance of TPAZ-TPE-COF is assigned to the effective suppression of nonradiative pathways, especially those arising from interlayer stacking and bond vibrations. These findings pave the way for deliberate construction of imine-linked 2D COFs with high PL intensity, thereby expanding the portfolio of luminescent COFs with potential applications in sensing and optoelectronics.