Dimensionality‐Dependent Pressure‐Induced Emission Memory in Covalent Organic Frameworks

Stimuli-responsive luminescent materials with memory effects hold significant promise for advanced applications in optical data storage and pressure sensing. We present the first crystalline covalent organic frameworks (COFs) exhibiting a pressure-induced emission memory effect, characterized by persistent pressure-induced emission enhancement (PIEE) that remains after decompression. Through the synthesis of a dimensional series of tetraphenylethylene-based COFs-JUC-730 and JUC-731 (one-dimensional, 1D), JUC-732 (two-dimensional, 2D), and JUC-733 (three-dimensional, 3D)-we systematically investigated how framework dimensionality governs photophysical responses under hydrostatic pressure. Remarkably, the 1D COFs exhibit pronounced PIEE, with JUC-730 retaining a 2.4-fold fluorescence enhancement post-decompression, representing the first observation of an emission memory effect in COFs. In situ FT-IR, powder X-ray diffraction (PXRD), and DFT analyses demonstrate that this memory effect originates from anisotropic unit-cell contraction, facilitated by conformational locking of flexible aryl-O-aryl (C-O-C) linkages in JUC-730, which results in a binding energy of ∼4.79 eV that stabilizes the emissive state. By contrast, the 2D and 3D COFs either undergo fluorescence quenching or fail to retain emission enhancement due to irreversible structural changes. These results establish a clear structure-dimensionality-function relationship and provide a design strategy for mechanically programmable luminescent materials with tailored pressure-responsive properties.