Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts

“United we stand, divided we fall.”–Aesop.Aggregation‐induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non‐emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM‐based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high‐tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed. “United we stand, divided we fall!” Aggregate formation changes non‐emissive luminogens to efficient emitters – this process is referred to as aggregation‐induced emission (AIE). The AIE effect is caused by the restriction of intramolecular motions of luminogens in aggregate state. The AIE materials have found a wide variety of high‐tech applications in the areas of optoelectronics, chemosensors, and biomedical probes.