Red and near infrared emission materials with AIE characteristics
Aggregation-induced emission (AIE) materials show faint emission or even non-emission when dissolved in good solvents but strong emission in the aggregate and/or solid states. Owing to the bright solid-state luminescence and a unique emission “turn on” process, AIE materials have captured scientists' intensive attention since the report of the AIE phenomenon in 2001. A great quantity of AIE molecules have been synthesized and widely applied in many areas such as organic light-emitting devices (OLEDs), chemical sensors, fluorescence bioimaging and diagnosis. Whereas, the vast majority of AIE luminogens are blue or green emissive, only few emit red light. However, red and near infrared (NIR) emissive AIE materials are highly important in the fields of full-color display and bioimaging. As one of the three primary colours, red is an indispensable element in the areas of full-color display systems and white-light lightings. Besides their application in optoelectronic devices, red/NIR-emitting materials are promising fluorescence probes in biology due to their large penetration depth, faint background autofluorescence and trivial irradiation harm to cells. The nanoparticles based on red/NIR emissive AIE materials possess high resistance to photobleaching, low toxicity and efficient emission, which are expected to be alternatives to inorganic quantum dots in the fields of biological assays and bioimaging. Therefore, the design and preparation of red/NIR emissive AIE materials have recently become a hot topic. This review summarizes the advances in red/NIR emissive AIE materials from the viewpoint of molecular design, and puts forward proposals for the future development of red/NIR emissive AIE materials.