New repertoire of 'donor-two-acceptor' NIR fluorogenic dyes.

Dye molecules with various fluorescent wavelengths are widely used for diagnostic and optical imaging applications. Accordingly, there is a constant demand for fluorogenic dyes with new properties. We have recently developed a novel strategy for the design of long-wavelength fluorescent dyes with a turn-ON option. The design is based on a donor-two-acceptor π-electron system that can undergo an internal charge transfer to form a new fluorochrome with an extended π-conjugated system. Here, we describe a series of such dyes based on two novel latent donors, naphthol and hydroxycoumarin. One of the dyes has showed excellent near-infrared fluorescent characteristics and specifically was demonstrated as a mitochondrial imaging reagent in live cells. This unique strategy for fluorogenic dye design has opened new doors for further near-infrared fluorescence probe discovery.