Cyclo-Ketal Xanthene Dyes: A New Class of Near-Infrared Fluorophores for Super-Resolution Imaging of Live Cells.

Newly emerging super-resolution imaging techniques provide opportunities for precise observations on cellular microstructures. However, they also impose severe demands on fluorophores. Here, we develop a new series of NIR xanthene dyes, named as KRhs, by replacing the 10-position O of rhodamines with a cyclo-ketal. KRhs display an intense NIR emission peak at 700 nm with fluorescence quantum yields up to 0.64. More importantly, they, without the aid of enhancing buffer, exhibit stochastic fluorescence off-on switches to support time-resolved localization of single fluorophore. KRhs are functionalized into KRh-MitoFix, KRh-Mem and KRh-Halo that demonstrate mitochondria, plasma membrane and fusion protein targeting ability, respectively. Consequently, these KRh probes demonstrate straightforward usage for super-resolution imaging of these targets in live cells. Therefore, KRhs merit future development for fluorescence labeling and super-resolution imaging in the NIR region.