Fluorescence Visualization of Strain by Tetraphenylethylene/Ruthenium Complex Three-Dimensional Covalent Organic Framework Assemblies

Dynamic visualization of strain and its distribution in materials are still challenging. Herein, dual-fluorophore three-dimensional covalent organic frameworks (3D-COFs) and the PEGylated 3D-COFs (PEG-3D-COFs) were synthesized for the construction of physically interacted assemblies to realize fluorescence imaging on not only strain distribution but also strain-related surface friction and flow velocity distributions in various media including polymer elastomers, organic or aqueous dispersions. The responsiveness arises from the controllability of the aggregation structure of 3D-COFs and PEG-3D-COFs, showing concentration-dependent morphology and photoluminescence, and meanwhile having a concentration-deformation equivalence on the structural evolution dynamics which drives the color change of the COF emission in the solids and liquids with high sensitivity and reversibility, whenever the superstructure of the COF assemblies is affected by the applied strain on the matrices. The report will inspire further efforts to construct responsive COFs for optical measurement aims.