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Recent Advances in Two‐Photon AIEgens and Their Application in Biological Systems

Two‐photon fluorescence imaging technology has the advantages of high light stability, little light damage, and high spatiotemporal resolution, which make it a powerful biological analysis method. However, due to the high concentration or aggregation state of traditional organic light‐emitting molecules, the fluorescence intensity is easily reduced or disappears completely, and is not conducive to optimal application. The concept of aggregation‐induced emission (AIE) provides a solution to the problem of aggregation‐induced luminescence quenching (ACQ), and realizes the high fluorescence quantum yield of luminescent molecules in the aggregation state. In addition, two‐photon absorption properties can readily be improved just by increasing the loading content of AIE fluorogen (AIEgen). Therefore, the design and preparation of two‐photon fluorescence probes based on AIEgen to achieve high‐efficiency fluorescence imaging in vitro/in vivo has become a major research hotspot. This review aims to summarize representative two‐photon AIEgens based on triphenylamine, tetraphenylethene, quinoline, naphthalene and other new structures from the past five years, and discuss their great potential in bioimaging applications.