AIE Characteristics of Closely Packed Benzylidene Dimethylbarbituric Acid Derivatives

Usually, solid-state fluorescence quenching is thought to be caused by pi-pi interaction. Hence, the common design strategies for materials with high-brightness solid-state luminescent rely on incorporating molecular rotors to weaken the intermolecular pi-pi packing. In this work, four types of BAs with the performance of solid-state fluorescence and without molecular rotors have been synthesized. Among them, B-4 was found to be a typical AIE compound and had a close cofacial packing mode, while it emitted strongly fluorescence in the solid state. The AIE characteristics of B-4 was attributed to more electron-donating groups and extended pi-conjugation. However, the other three BAs showed almost no fluorescence emission due to their more closed face-to-face packing mode or less electron-donating groups. These results indicated that tight stacking mode unnecessarily lead to fluorescence quenching. This study suggests there may be fewer constraints to develop new AIE materials, and there might be a large number of tightly packed AIE molecules.