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 (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. 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).