Effect of molecular conformation-changing on mechanochromism in tetraphenylethene substituted carbazole units

Mechanochromism material is an important branch of intelligent materials. But it appears late and its development has encountered a bottleneck due to the low fluorescence quantum yield in solid-state and unclear color-changing mechanism. In this work, we proposed a molecular conformation-changing strategy for preparing mechanochromism materials with high solid-state luminescent efficiency. And three compounds (CPE-1, CPE-2, and CPE-4) with tetraphenylethene (TPE) and carbazole units were synthesized. Thanks to the aggregation-induced emission luminogen (AIEgen) TPE unit, CPE-1, CPE-2, and CPE-4 had robust solid-state emission. CPE-4 showed excellent mechanochromism characteristic, which was better than that of CPE-2 and CPE-1. It may be that the relatively large size of carbazole could tune the twisting in the molecules, which further affected the molecular arrangements. Density Functional Theory, Scanning Electron Microscope, and X-Ray Diffraction results showed that mechanochromism characteristic is related to the alterations of molecular conformations and packing modes under mechanical stimuli. Finally, CPE-4 with reversible mechanochromism property was successfully applied in fluorescence writing, which illustrated the success of molecular conformation-changing strategy.