Schiff base particles with aggregation-induced enhanced emission: random aggregation preventing π–π stacking

Three Schiff bases containing phenylbenzoxazole were synthesized and characterized, which exhibited distinct aggregation-induced enhanced emission (AIEE) behavior in THF-water. However, the single-crystals of L3 show obvious pi - pi stacking that would induce fluorescent quenching in the solid state. In order to further gain insight into the AIEE mechanism of the three compounds, the size and growth process of particles with different water fractions were studied using SEM, TEM and DLS. The results show that the molecules of compounds can slowly assemble in an ordered fashion to form more-crystalline but less-emissive particles in the THF-water mixtures with low water contents, while in mixtures containing very large amounts of water, the molecules of compounds abruptly agglomerate to form less-crystalline or even amorphous but more-emissive clusters, which effectively avoid pi - pi stacking.