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.