Deep-red to near-infrared fluorescent dyes: Synthesis, photophysical properties, and application in cell imaging

• Four deep-red or near-infrared fluorescent dyes were designed and synthesized.
• Carboxylic groups in the dyes improved water solubility and facilitated labeling.
• The photophysical properties of the CPC dyes were investigated in details.
• CPC1E and CPC2E could selectively stain lysosomes with good photostability.

More and more attention has been paid to the design of new fluorescent imaging agents with good photostability and water solubility, especially those with emissions in the deep-red and near-infrared regions. In this work, we designed and synthesized four novel fluorescent dyes with deep-red or NIR fluorescence by hybridizing coumarin and pyronin moieties based on our previous work. Introduction of carboxylic acid in the dyes not only imparted the dyes with water solubility but also provided a versatile sensing platform for designing the fluorescent probes and sensors of biomolecules. The photophysical properties of these new dyes were investigated through absorption and fluorescence spectroscopy. Cell imaging experiments showed that esterification products could selectively stain lysosomes with good photostability, thereby indicating that they could be useful in the development of fluorescent probes for bioimaging.

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