High contrast mechanofluorochromic behavior of new tetraphenylethene-based Schiff base derivatives

New tetraphenylethene-based Schiff base ligand (TPE-ND) and its corresponding boronated complex (TPE-NDB) with aggregation-induced emission were designed and synthesized. Results showed that the inhibited C=N isomerization by N, O-chelated BF2 caused the significant intramolecular charge transfer features, and more dramatic solvatochromism. In particular, the solid sample of TPE-NDB exhibited an obvious mechanofluorochromic behavior. Upon grinding with a spatula, the as-prepared powder sample illustrated a remarkable red shift of 97 nm, with considerable color contrast from bright green (498 nm) to orange (595 nm). Its fluorescence color can be reversibly switched by repeating the grinding-fuming process. The mechanochromism is attributed to the phase transformation between amorphous and crystalline states. The practical application indicated that TPE-NDB has excellent mechanofluorochromic properties, and it can be utilized as optical recording materials.