Research on the Mechanism of Aggregation-Induced Emission through Supramolecular Metal-Organic Frameworks with Mechanoluminescent Properties and Application in Press-Jet Printing

This study investigates the mechanism of AIE in the solid state through supramolecular metal-organic frameworks and mechanoluminescent materials for the first time. Herein, four novel differently substituted Schiff base building blocks, SB1-SB4, exhibit typical AIE properties with various fluorescence emissions from yellow to green. SB1-SB4 are linked through C-H···O hydrogen bonding interactions to construct supramolecular metal-organic frameworks (SMOFs): namely, SMOFSB1-SMOFSB4. Particularly, among these SMOFs, SMOFSB3 is observed to have micropores in the 3D supramolecular structure and exhibits mechanoluminescent properties (grinding). An emission turn-on mechanism occurs with destruction of micropores by grinding and blockage of intramolecular rotations of the methyl and acetonitrile in the micropores, resulting in emission turn-on in SMOFSB3. Single-crystal X-ray structures, powder X-ray diffraction, emission spectra at room temperature, temperature-dependent emission spectra, DFT calculations, and a charge separation hypothesis well demonstrate the emission turn-on mechanism, which is consistent with the mechanism of AIE. More importantly, the molecules demonstrated potential application for press-jet printing.