AIE activity, mechanochromic property and solvent inclusion of two β-diketones with tetraphenylethylene unit

Highly twisted molecular conformation easily leads to the loose molecular packing and big voids, which are desirable for mechanochromism and solvent inclusion. Here, TPE-BF and TPE-BT with highly twisted molecular conformation were designed and synthesized by α-substitution of two β-diketonates. TPE-BF and TPE-BT show similar aggregation-induced emission activity, but different mechanochromism. Subsequently, the corresponding internal mechanism are analyzed and discussed in-depth by XRD, DSC, fluorescence lifetime, crystal analysis and theoretical calculation. Compared with crystal TPE-BF, crystal TPE-BT exhibits more obvious mechanochromism (red shift of 12 nm) before/after grinding, which is attributed to EtOAc inclusion and different intermolecular interactions and stacking. Furthermore, wavelength shifts of TPE-BF and TPE-BT do not exceed 35 nm after phase transition from crystalline state to amorphous state. Obviously, highly twisted molecular conformations fail to bring about high-contrast mechanochromism (wavelength shift above 100 nm), whose reason should be the suppressed intermolecular π-π interactions and overlap before/after grinding. Combined with previous research results of our laboratory, the luminogens forming solvent inclusion generally have twisted molecular conformation, and similar structural fragment with solvent molecule, which will provide a potential design strategy for selective solvent inclusion.