Restricted Intramolecular Rotations: a Mechanism for Aggregation-Induced Emission

This chapter reviews restricted intramolecular rotation (RIR), the mechanism model for the aggregation-induced emission (AIE) phenomenon. The structural features of 2,3,4,5-tetraphenylsiloles, the protocol AIE molecules, are analyzed. Key experimental results that supported the RIR model are discussed, and RIR was found to play a crucial role in the light emissions of small silole molecules and silole-containing polymers. The RIR mechanistic picture predicts that the AIE effect should not be a special attribute of silole-based molecules and polymers but a common property of many luminogens with similar structural features. Moreover, based on the RIR mechanistic picture, AIE luminogens have found many important applications, such as in chemical sensors, biological probes, smart nanomaterials and solid-state emitters in organic light-emitting diodes (OLEDs), where the manner of restriction or activation of the intramolecular rotations would be the major concern.