Insights into Optical Probes Based on Aggregation-Induced Emission: from Restriction of Intramolecular Motions to Dark State

Since the exposure of the concept of aggregation-induced emission (AIE) to the scientific community in 2001, AIE fluorophores attract much attention for biological imaging, detection, and advanced material fabrications. Some efforts have been devoted to the mechanism studies on the luminescence nature of AIE fluorophores. Restriction of intramolecular motions (RIM) can explain the luminescence mechanism at a relatively large level and has been recognized as the general working mechanism of AIE. To disclose the connotation of the RIM mechanism, an in-depth study to elucidate the dark state of AIE molecules is needed. In this review, the recent progress of luminescence quenching mechanisms for AIE molecules is summarized and compendiously categorized into four parts, which are: restriction of access to dark state (RADS), restricted access to a conical intersection (RACI), restrict molecules from entering twisted intramolecular charge transfer (TICT) state, and excited state intramolecular proton transfer (ESIPT) coupled with TICT state, respectively. These insights and systematical elucidation of the emission quenching in the view of dark state are of great significance for fundamental understanding. It is hoped that this feature article will attract more researcher's interests and open up new vistas for the development of aggregate science.

Automated summary

AIE fluorophores have attracted attention for biological imaging, detection, and material fabrications since the concept was introduced in 2001. The luminescence mechanism of AIE fluorophores is mainly explained by the restriction of intramolecular motions (RIM). Understanding the dark state of AIE molecules is crucial for fundamental understanding and development in aggregate science.