Fluorinated phenothiazine derivatives: Photophysical properties, mechanochromism and thermochromism

Three fluorinated phenothiazine compounds (P-1, P-2, P-3) were synthesized and characterized. It was found that all of them displayed significant solvatochromism and aggregation-induced emission behaviors. It was worth noting that P-1 and P-2 exhibited obvious mechanochromic properties compared to P-3. Specifically, P-1 displayed two different colors upon grinding and smashing, and emission bands showed different shift direction. P-2 exhibited polymorphic emission, its powder emitted yellow fluorescence, whereas crystal emitted orange fluorescence. After grinding, these two states had red shifts of 76 nm and 35 nm, respectively. But P-3 only presented a red shift of 10 nm. In addition, P-1 and P-2 also had thermochromic properties. After heating, their maximum emission wavelengths all would red-shift, and the maximum red shift can be up to 71 nm. These results can be explained by wide-angle X-ray diffraction, the differential scanning calorimetry and single crystal diffraction analysis. This work provided a new idea for the preparation of materials with both mechanochromic and thermochromic characteristics.