I've had about one liter of fluorescein solution setting on the shelf for at least several years and one day noticed that it suddenly lost its characteristic green color. It's now a light yellowish-green solution that seems to have lost the property of fluorescence altogether.

The container is a reagent bottle with a leak-proof cap so I doubt that the solution reacted with anything in the atmosphere other than maybe 100 mL of air that was in the bottle to begin with.

The bottle was exposed to direct and indirect sunlight on a daily basis.

Does it have to do with the decomposition of the fluorescein, and if so, what are the expected decomposition products?

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    $\begingroup$ Have you investigated what happens if you add a little NaOH to some of the solution? If the color and fluorescence is restored, it might have been a change in pH, perhaps caused by the very slow reaction with a glass container. Good question! Please post your findings. $\endgroup$ Feb 15, 2015 at 22:34
  • $\begingroup$ @DrMoishePippik I will try that and get back to you. Thanks for the idea. $\endgroup$
    – docscience
    Feb 15, 2015 at 23:44
  • $\begingroup$ @DrMoishePippik That was a no-go on the NaOH. Increasing the pH did not restore the fluorescence. $\endgroup$
    – docscience
    Feb 16, 2015 at 23:24

1 Answer 1


Yes, Fluorescein decomposes due to exposure to light.

See The Conservative Behavior of Fluorescein for quantitative data.


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