Highly photostable ketopyrrolyl-BODIPYs with red aggregation-induced emission characteristics for ultrafast wash-free mitochondria-targeted bioimaging

Subcellular organelle-specific probes, including mitochondria-targeted fluorescent probes, have attracted enormous research interests because they can monitor or visualize the morphology or biological activities of specific organelles and play an indispensable role in disease diagnosis. To follow the process, highly specific and photostable fluorescent probes are in demand. However, commercially available mitochondria probes normally suffer from poor photostability under laser irradiation and aggregation caused quenching (ACQ) in the aggregate state. In this work, two simple aggregation-induced emission(AIE)-active meso-2-ketopyrrolyl BODIPYs were developed via a convenient one-pot synthetic procedure from 2-methylpyrrole and corresponding pyrrolyldiketone in the presence of BF₃·OEt₂. The two AIE luminogens (AIEgens) both show very weak fluorescence (maximum emission peaks at 545 and 559 nm, respectively) in DMSO and strong near-infrared solid-state emission. The fluorescence was dramatically intensified and redshifted to 635 and 643 nm, respectively, when water fraction was increased up to above 95% in the DMSO/water mixtures. Both AIEgens were found to specifically “light up” the cell mitochondria with high biocompatibility. Interestingly, the staining process can be shortened for less than a minute after the addition of the AIEgens and without the involvement of a washing procedure, indicating an ultrafast and easy-to-operate staining protocol. Furthermore, their fluorescent images in deep tissue penetration were captured with a satisfied signal-to-noise ratio at a depth of 20 and 30 μm along the direction of the z-axis. Importantly, both AIEgens exhibit high photostability under harsh continuous laser irradiation, demonstrating their potential application as in visualizing and tracking specific mitochondria-associated dynamic changes.