Aggregation-induced emission fluorophores towards the second near-infrared optical windows with suppressed imaging background

Fluorescence bioimaging in the second near-infrared (NIR-II) region can visualize deep bioinformation in real time with high sensitivity. Especially, NIR-IIa (1300–1400 nm) and NIR-IIb (1500–1700 nm) windows possess extremely low imaging background and have attracted much research interest recently. Towards the two imaging windows, NIR-IIa or NIR-IIb emissive fluorescent probes for biomedical research and translational applications have been increasingly explored, along with which the enough integrated NIR-IIa or NIR-IIb fluorescence intensities become one of the key points. Among many NIR fluorescent materials, organic fluorescent nanoprobes with aggregation-induced emission (AIE) properties are widely used in biomedical imaging research due to the tunable spectral responses, high brightness, and low biological toxicity. This review focuses on the structure design of AIE molecule with ultra-bright NIR-IIa or NIR-IIb emission and the AIE fluorophores assisted NIR-IIa or NIR-IIb bioimaging applications. In addition, the development prospects and current challenges in this new field are given. It is hoped that this review can encourage more innovative designs of NIR-IIa or NIR-IIb luminescent materials and meaningful bioimaging applications.