Aggregation-induced emission
Aggregation-induced emission (AIE) is an abnormal phenomenon that is observed with certain organic luminophores (fluorescent dyes). Most organic compounds have planar structures and higher photoemission efficiencies in solution than in the solid state. Otherwise said, these fluorophores or fluorescent dyes are much more emissive in solution compared to just the solid form, in that the intensity of their emission is greater in solution. However, some organic luminophores have freely-rotating groups (rotational degrees of freedom), when these molecules are excited instead of releasing that energy as light they relax back down through these rotations. When these  luminophores aggregate or crystallize, which restricts those rotations, they can become very fluorescent or emissive, and the photoluminescence efficiency (i.e. quantum yield) increases. Aggregation-induced emission enhancement. The phenomenon in which organic luminophores show higher photoluminescence efficiency in the aggregated state than in solution is called aggregation-induced emission enhancement (AIEE). Some luminophores, e.g., diketopyrrolopyrrole-based and sulfonamide-based luminophores, only display enhanced emission upon entering the crystalline state. That is, these luminophores are said to exhibit crystallization-induced emission enhancement (CIEE). Luminophores such as noble metallic nanoclusters show higher photoluminescence efficiency in the aggregated state than homogenous dispersion in  solution. This phenomenon is known as Aggregation-Induced Emission (AIE). Aggregation-induced emission Polymer. Fluorescence-emission Polymer is a kind of polymer which can absorb light of certain frequency and then give out light. These polymers can be applied in biomaterial area. Due to their high biocapacity and fluorescence, they can help researchers to find and mark the location of proteins. And polymers with property of aggregation-induced emission can also help to protect the healthy tissues from the harm of the medicines.