Confinement fluorescence effect (CFE): Lighting up life by enhancing the absorbed photon energy utilization efficiency of fluorophores

The absorption photon energy utilization efficiency of small molecule fluorophores can be enhanced only through the conformational change of a single molecule (without destruction/aggregation/assembly/packing). Therefore, the so-called confinement fluorescence effect (CFE) can be used as an used as a useful sensing strategy for bio-sensing/imaging probes to light up life without a change in molecule structure. So far, many scientists have carried out a great proportion of their work making use of this property of fluorescent molecules. In recent years, vibration-induced emission (VIE), dissociation-induced emission (DIE), rigidification-induced emission, changes in motion-induced change in emission (MICE), assembling-induced emission, molecular binding set identification characteristics (MUSIC), especially the term used for the generation of emission by aggregation (aggregation-induced emission, AIE), have contributed to a better understanding of fluorescence sensing mechanisms. However, as a universal concept, the CFE has not been systematically summarized. Herein, we focus on describing the concepts and characteristics of CFEs, demonstrate their various applications, present unique advantages of CFE-based organic small molecule fluorophores, and discuss the technical challenges encountered in this area of research. We hope that the review will promote a deeper comprehension of CFEs, enable the construction of strategies for various luminescent materials, and facilitate the development of advanced fluorescent functional materials.