Intracellular imaging of organelles with new water-soluble benzophenoxazine dyes

Five new water-soluble derivatives of Nile Red 1–5 were prepared. These benzophenoxazine dyes fluoresce between 640 and 667 nm with quantum yields of 0.17–0.33 in pH 7.4 phosphate buffer, and at slightly shorter wavelengths and higher quantum yields in EtOH. Two dyes, 3 and 4 permeated into Clone 9 cells and selectively stained mitochondria and golgi, respectively.