Lavender violet, blue and pink: A new type of benzo[a]phenoxazine-based dipolar, red-emitting dyes

•A new type of red-emitting benzo[a]phenoxazine-based dyes has been developed, namely Lavender Violet, Blue, and Pink.•The new dyes are dipolar analogues of Meldola's Blue and structurally relevant with Nile Blue and its derivatives.•One of the Lavender Violets emits in the far-red region and shows bright cellular images as observed by CLSM.

A new type of the red-emitting benzo[a]phenoxazine-based dyes, dipolar analogues of Meldola's Blue, are synthesized by condensation of p-nitrosoanilines or p-nitrosophenol with 7-(alkylamino)naphthalen-2-ol in good yields. Their photophysical properties are characterized by the donor substituents introduced, offering dyes of lavender violet, blue, and pink colors. These dyes exhibit high absorptivity, marginal-to-good optical brightness, good photostability, and show large Stokes shifts in aqueous solution. One of the dyes emits bright red fluorescence inside cells, as observed by confocal laser scanning microscopy (CLSM). The new dyes thus have potential to be used for staining purposes including cellular imaging.

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