Re-recognizing fluorescence quenching Units: Improve abnormally the luminescent efficiency of AIEgens for fluorescence Sensing, organelle targeted imaging and photodynamic therapy

Fluorescence quenching phenomenon caused by the heavy atom effect and intramolecular charge transfer (ICT) is a classical and generally recognized photophysical phenomenon. However, its universality is not observed in some special aggregation-induced emission luminogens (AIEgens). Herein, a series of cyanostyrene (CST)-based AIEgens were designed and synthesized by coupling different electronic donors and fluorescent quenching groups at both ends of the CST "bridge". By studying clearly of structure-properties relationship of materials, the performance of full-wavelength emission from deep blue to far red could be achieved by regulating the excited state. Intriguingly, the introduction of fluorescent quenching groups of bromine (Br) and nitro (NO2) in the CSTs induced abnormal fluorescence enhancement, which broke the conventional rule of quenching fluorescence brought from the above-mentioned quenching units. In addition, the introduction of quenching groups was beneficial for boosting reactive oxygen species (ROS) generation by activating intersystem crossing (ISC) channel to produce more triplet excitons, effectively. In view of special chemical structure contained alkaline group as well as clear photophysical performances, some representative CST-based emitters were chosen to explore advanced applications such as information encryption, fluorescent sensor of detecting hydrogen chloride and biological amines, cellular fluorescent imaging of simultaneous target to lysosome and mitochondria, and effective photodynamic therapy (PDT) to treat cancer cells. This work revealed that conventional rule of heavy atom effect and strong ICT effect to quench fluorescence is not suitable for some unique CST-based AIEgens, which plays important role in liberating our inherent cognition to design novel special functional materials in the future.