Fine-tuning the mechanofluorochromic properties of benzothiadiazole-cored cyano-substituted diphenylethene derivatives through D-A effect

We synthesized three new benzothiadiazole-cored cyano-substituted diphenylethene derivatives (PT-OMe, PT-H, and PT-CF3) with different methoxy, hydrogen, and trifluoromethyl end groups, and the synthesis confirmed by standard spectroscopic methods. These end groups endowed them with different donor-acceptor (D-A) effects, and they provide them with a peculiar and completely opposite mechanofluorochromic property. Red-shifted mechanofluorochromic features were found in the PT-OMe and PT-H compounds, while on the contrary, PT-CF3 showed blue-shifted mechanofluorochromic behavior. The mechanofluorochromic mechanism was explored and attributed to the metastable state of the ground compounds and the crystalline-amorphous phase transformation between the original and ground states. Moreover, these derivatives showed reversible significant mechanofluorochromic properties and reproducibility between ground and annealed states, making them promising stimuli-responsive and smart luminescent materials for mechanosensors, fluorescence switches and light-emitting device applications. The introduction of the D-A effect strategy demonstrated in this work would provide a new path to fine tune the optical features of mechanofluorochromic materials with unique and diverse fluorescent properties.