Fundamental principles of AIE

A rational decipherment of AIE mechanisms is of great importance to understand luminescence processes, design novel luminogens, and explore advanced practical applications. Initially, a number of possible working mechanisms were hypothesized, such as restriction of intramolecular rotation (RIR), J-aggregation, conformational planarization, E/Z isomerization, twisted intramolecular charge transfer (TICT), and excited-state intramolecular proton transfer (ESIPT). However, most of them were only applicable to limited AIE systems. Thereafter, the restriction of intramolecular vibrations (RIV) was also proposed to explain some AIE processes. In this chapter, the two main mechanistic causes of AIE effects are summarized, RIR and RIV, which could be unified as a restriction of intramolecular motion (RIM). Some experimental and theoretical works are also elucidated to provide solid evidence.