Functionality and versatility of aggregation-induced emission luminogens

Breakthrough innovations in light-emitting materials have opened new exciting avenues for science and technology over the last few decades. Aggregation-induced emission (AIE) represents one of such innovations. It refers to a unique light-emitting phenomenon, in which luminescent materials that are non-emissive in molecular state can be induced to emit efficiently in aggregated state. The design and development of AIE luminogens (AIEgens) have overcome technical and fundamental limitations that exist in conventional light-emitting materials, and thus generate great opportunities for various applications. In this review, we aim to introduce the wonderful world of AIE to scientists from different disciplines by summarizing the recent progress made in this exciting research field. The mechanistic analyses and the working principles of the AIE processes are first elaborated, which reveal the restriction of intramolecular motions as the main cause for the AIE effect. The different molecular engineering strategies for the design of new AIEgens are subsequently discussed with examples of various AIEgen systems. The recent high-tech applications of AIEgens as optoelectronic materials, chemical sensors, and biomedical probes are presented and discussed. We hope that this review will stimulate more research interest from physics, chemistry, life science, and biomedical fields to this wonderland of AIE.