Aggregate Science: Much to Explore in the Meso World

Summary Researchers face challenges and opportunities in assembling microscopic molecules into macroscopic substances, during which original properties may disappear and new properties may emerge. To understand the science in the middle, studies on mesoscopic aggregates are needed. Research on aggregation-induced emission (AIE) is an ideal entry point for scientists to explore and unravel the mysteries of the meso world, because AIE is a typical phenomenon showing a non-linear property change from molecules to aggregates. AIE luminogens often show no emission in solutions at the molecular level but become brightly emissive when they form mesoscopic aggregates. Aggregation processes generally involve the interplay of competitive or cooperative effects, and new structures, properties, and functions usually appear and diversify in aggregates. In this perspective, four effects, including antagonism, synergism, emergence, and divergence, are abstracted out and instanced by different AIE systems to develop aggregate science and stimulate new ideas from a broad readership.