Dibenzthiophene and carbazole modified dicyanoethylene derivative exhibiting aggregation-induced emission enhancement and mechanochromic luminescence

A novel D-A type dicyanoethylene derivative DBT-Cz-DCN was designed and synthesized using dibenzthiophene, dicyanoethylene and carbazole as raw materials. Photophysical studies indicated that the luminogen DBT-CzDCN possessed unique intramolecular charge transfer (ICT) characteristic from electron donating carbazole unit to electron accepting dicyanoethylene moiety and aggregation-induced emission enhancement (AIEE) property. Theoretical calculations indicated that DBT-Cz-DCN exhibited a highly twisted conformation due to the steric hindrance effect of the dicyanoethylene unit. It was worth noting that DBT-Cz-DCN also exhibited distinct mechanochromic luminescence property. Specifically, when the pristine powder of DBT-Cz-DCN underwent grinding, the emitting color shifted from yellow to orange-yellow. The emitting color and wavelength could be restored to the pristine state after fuming with dichloromethane vapor. Powder X-ray diffraction confirmed that the transformation between the amorphous state and the crystalline state under external force stimuli was the reason for the MCL (mechanochromic luminescent) behavior of DBT-Cz-DCN. The current work not only developed a novel molecular structure with AIEE characteristic and MCL behavior, but also laid the foundation for the development of MCL materials with high contrast, high luminescence efficiency and good reversibility.