Question

what is the effect of pH on fluorescence intensity and wavelength maximum for fluorescein

Answer 1

pH may have a significant effect the fluorescence intensity and wavelength maximum for fluorescein. Since in some cases the protonated form of weak bases and or the unprotonated form of weak acids may be non-fluorescent.

For example:

Although commonly referred to as fluorescein, the dye used for fluorescein angiography is actually fluorescein sodium (C₂₀ H₁₀ Na₂ O₅).Itis the water-soluble salt of fluorescein, a member of the xanthene group of dyes, it is a highly fluorescent chemical compound synthesized from the petroleum derivatives resorcinol and phthalic anhydride.

Fluorescein sodium absorbs blue light, with peak excitation occurring at wavelengths between 465-490 nm. The resulting fluorescence occurs at the yellow-green wavelengths of 520 to 530 nm. pH can affect the intensity of fluorescence. Maximum fluorescence occurs at a pH of 7.4, but the pH of fluorescein sodium for angiographic use is adjusted to a range of 8 to 9.8 for stability.