A dye, Phloxine B, a common food coloring and one of the active components of a photoreactive insecticide was recently approved by Food and Drug Administration as D&C Red #28 for use in drugs and cosmetics. Phloxine B is also one of the most widely use stain in fluorescence microscopy. However, in spite of the widespread interest in multi-photon spectroscopy and imaging, no information is available on the electronic transitions properties of Phloxine B with red edge fluorescence excitation and with multi-photon excitation.

In the present report we described the steady state and time-resolved fluorescent properties of Phloxine B with up-convert photon excitation and with two-photon excitation. We examined the electronic transitions properties of Phloxine B when was excited by femtosecond pulses from a mode-locked titanium sapphire laser or a mode-locked optical parametric oscillator laser. Phloxine B under excitation wavelengths above 775 nm was found to display two-photon excitation fluorescence with a spectrum maximum at 580 nm, which emission is consistent with one-photon excitation fluorescence spectrum. At the red edge excitation of Phloxine B, from 590 nm to 650 nm, we observed one-photon excitation fluorescence indicating that Phloxine B behaves like upconverting dye with one-photon excitation process.