Triphenylamine functionalized β-Ketoiminate boron complex exhibiting aggregation-induced emission and mechanofluorochromism

Abstract

A new triphenylamine functionalized β-Ketoiminate boron complex BF2-TPA that bears the electron donor triphenylamine and the electron acceptor β-iminoenolate boron moiety, has been designed and successfully synthesized. The D–π–A type conjugated compound showed obvious intramolecular charge transfer (ICT) properties, which were evidenced by theoretical calculations and spectral analysis. The compound exhibited evident AIE characteristic with high fluorescence quantum yield in the solid state. BF2-TPA was quite weakly fluorescent in THF, while a significant AIE effect was observed in water/THF (fw = 70%) mixtures with a large AIE factor of 188. Interestingly, BF2-TPA possesses the distinct mechanofluorochromic (MFC) behavior. The as-prepared powder of BF2-TPA could emit strong yellow light centered at 549 nm under UV irradiation, and the fluorescence color changed into orange (590 nm) after grinding, a red shift of 41 nm was observed. Such mechanochromism was reversible upon the treatment of grinding and fuming with CH2Cl2. The powder XRD studies showed that the MFC nature is generated through crystalline–amorphous phase transformation under the stimulus of external force. The relationship between the structure and the properties was studied in detail. The results obtained would be of great help in understanding the MFC mechanism and designing new MFC materials.