A new approach to switchable photochromic materials by combining photochromism and piezochromism together in an AIE-active molecule

A carbazole containing triphenylethylene derivative (TrPEBCar) has been designed and synthesized, which combines aggregation-induced emission (AIE), piezochromism and photochromism together. In the crystalline state, an intensive emission band at 448 nm was detected. After pressing the crystalline solid, a [crystalline–amorphous] morphological transition takes place, in which the resulting amorphous state of TrPEBCar exhibits a different color and a red-shifted emission band at 470 nm. Photochromic behavior of TrPEBCar is achieved by utilizing a stilbene-type intramolecular photocyclization in the crystalline state. In addition, we report for the first time morphology-dependent photochromism, in which the photochromic properties of TrPEBCar are only observed in the crystalline state but not in the amorphous state. Therefore, the methods of pressing/fuming and heating/fuming act as gates to switch the photochromic properties by changing the aggregation states between the crystalline and amorphous states. By combining the piezochromic properties with the photochromic properties, the ON/OFF states of TrPEBCar can easily be observed by the different colors and emission properties. The triphenylethylene derivative with simple molecular structure provides a new approach for gated photochromic materials with both switch and indicator.