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Fluorescein colour[edit]

In slit lamp, based on an article from the NIH MedlinePlus medical encyclopedia, it is stated that flourescein is orange-coloured, but in this article it is used to colour a river green? Which is it? Dewet 15:34, 16 May 2005 (UTC)Reply[reply]

It's both. :) Pure fluorescein is a red-orange crystalline substance. In water or ethanol solution, it's green or yellow-green depending on the solvent and pH. --TenOfAllTrades (talk/contrib) 16:07, 16 May 2005 (UTC)Reply[reply]
Actually even in solution fluorscein is orange (just have a look at the picture included in the article). The greenish look it has, is it's fluorescent light emission. Chris
Ah, many thanks, then. I'll leave it as is. Dewet 16:59, 16 May 2005 (UTC)Reply[reply]
At lower concentrations (uM), a fluorescein solution has a green yellowish color. As the dye concentration increases (mM), the solution appears orange. KingHanneman (talk) 04:57, 1 February 2008 (UTC)Reply[reply]

I'm pretty sure the wavelengths here are wrong. I think the absorption wavelength is 488 nm and emission 520nm. I haven't changed it as someone might change it back straight away :-) Dwayne Dibly 00:26, 21 December 2005 (UTC)Reply[reply]

Close Dwayne. I have some results of my own: abs = 491nm and emission = 514nm. It's probably better to find a literature value though. Tomid 16:38, 18 July 2006 (UTC)Reply[reply]
It's solvent dependent. Both the excitation and emission peaks shift a little based on solvent and pH. 490/520 nm are pretty accepted general areas, though. chihowa 01:44, 14 March 2007 (UTC)Reply[reply]

what causes fluorescence?[edit]

In the articles that I've looked at, they talk about how Fluorochromes, based on their chemical makeup, are able to absorb short wavelengths of light and emit long wavelenths of light, which then are visible. Why is this so? What is different about the structure of, for example, isothiocyanate, that it does emit light at longer wavelengths? Why do other compounds not do this? For example, why do some organisms, such as Cyanobacteria, fluoresce while others do not?

For answers to general reference questions, might I suggest placing a note at Wikipedia:Reference desk? More editors are likely to see your question there, and it's a more appropriate forum—the article Talk pages (like this one) are better suited for discussion that directly relates to the content of each article. With regard to your question, I'd also recommend starting with our article on fluorescence, and start following links from there. It's a pretty big topic. TenOfAllTrades(talk) 19:33, 9 August 2005 (UTC)Reply[reply]
Fluorescence of this dye is primarily due the fluorone segment, which is highly conjugated and increases the probability that relaxation from the excited state occurs through fluorescence. The isothiocyanate group on fluorescein is typically used for covalent attachment to polymers and in biology. As for the isothiocyanate group by itself, if it doesn't fluoresce, then it would primarily undergo non-radiative relaxation pathway(s) from the excited state. I think less than 10% of molecules fluoresce; even less fluoresce well (ie have a high quantum yield). KingHanneman (talk) 05:10, 1 February 2008 (UTC)Reply[reply]


Okay, I added the SMILES string, but it's pretty large and makes the chembox look ugly. I'm not very good at formating in Wikipedia so hopefully someone with more skill will be able to clean it up and make it look nice. :) Mrestko 21:23, 4 July 2006 (UTC)Reply[reply]

different abs and em peak positions[edit]

there are two different sets of adsorption and emission peak wavelengths mention in the article. Are the values under "chemical properties" related to FITC and not fluorescein? Benkeboy 10:39, 6 September 2006 (UTC)Reply[reply]


Apparently all the folks involved in using fluorescein dyes know that it has a low toxicity; presumably it wouldn't be poured into a river or injected into the bloodstream for eye photography if it were toxic. However, does it not bear comment in the article that such a dramatically colored chemical is harmless? Yes, it obviously is a relevant issue that should be explicated. I, for one, am curious about its toxicity thresholds. -PLK —The preceding unsigned comment was added by (talk) 21:41, 17 March 2007 (UTC).Reply[reply]

I was also missing information about that, good point.

Fluorescein may have low toxicity but that does not make it harmless. In some people, exposure triggers anaphylaxis. --Una Smith 03:09, 18 August 2007 (UTC)Reply[reply]

2',7' Fluorescein Derivatives[edit]

I don't know if this is useful or not, but in the work I'm doing now with fluorescein, I've read that the pKa of the dye can be controlled by the substituents in the 2' and 7' positions. For example, an electron withdrawing group decreases the pKa. The pKa for dichlorofluorescein is 5, and the pKa for difluorofluorescein (aka Oregon Green 488) is 4.7. Likewise, an electron donating group increases the pKa. An ethyl group increases the pKa 0.2-0.3 pH units, and a hexyl group increases the pKa to 8.4. Also, in water, the absorption and emission maxima shift a bit (~10 nm). KingHanneman (talk) 05:19, 1 February 2008 (UTC)Reply[reply]

Published Synthetic Procedures for Fluorescein and FITC[edit]

I was reviewing the publications cited on the Fluorescein page, and I could not find the published paper cited in reference 2 (Yuichiro Ueno, Practical Synthetic Procedures, etc.). I did find a preprint on the TAMU.EDU site, but I could not find the actual version as published. Could someone direct me to the proper page? Also, I thought I would add a reference for the synthesis of FITC, but I cannot find that reference. I find hundreds of papers on the preparation of FITC derivatives but none on the preparation of FITC itself. Could someone help me track that down? Thanks very much! RHWoodman (talk) 05:07, 10 September 2009 (UTC)Robert WoodmanReply[reply]

As an additive[edit]

The article doesn't mention its use as an additive to radiator coolant and perhaps some hydrocarbon fuels and oils, for leak detection. (Here is a reliable citation.) David Spector 02:54, 11 February 2010 (UTC)Reply[reply]

Fluorescein "absorption" spectrum[edit]

I've just noticed the spectra presented in this article are a bit odd. First the text underneath the graph states "absorption and emission" while the blue line is the excitation spectrum. Though absorption and excitation spectra are closely related, they are not equivalent. More importantly, a peak appears at 520 nm, which doesn't exist in the absorption spectrum of fluorescein. The reason for this is that the excitation spectrum was recorded for an emission wavelenght of 520 nm : this peak is due to the apparatus recording its own signal.

In my opinion, this graph should be removed and maybe replaced with normalised absorption/emission spectra (with precisions about medium and pH) rather than exctiation/emission. Julien (talk) 09:12, 22 August 2012 (UTC)Reply[reply]

External links modified[edit]

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Pictures on this page differ[edit]

The two structures shown for fluorescein on this page are quite different. I'm pretty sure the first one is incorrect. Can someone confirm and correct this? (talk) 12:10, 25 September 2018 (UTC)Reply[reply]

I agree, it is slightly confusing. Actually both forms are correct as fluorescein is pH sensitive and can exist in the colourless "spirolactone" form and the ring opened lactone form depending on the pH. See also leuco dye although that doesn't mention fluorescein. From memory at pH 7.4 the lactone is favoured so I will change the image to be more clear. Aloneinthewild (talk) 19:55, 27 September 2018 (UTC)Reply[reply]

Mistaken Structure[edit]

Upon googling and finding other sources, most other sources disagree with the structure shown here. instead of that Fluorescein in its raw form contains an ester instead of the carboxylate and a OH instead of a ketone. the molecule that seems to be shown is the intermediate when sodium fluoresite is neutralized into Fluorescein. The compound is ph sensitive shouldn't both structure be shown? please feel free to correct me I am not a professional only a hobby chemist and would love to understand

Use by plumbers[edit]

Plumbers use this dye to detect leaks in pipes. This should be mentioned.Wastrel Way (talk)Eric Wastrel Way (talk) 14:11, 11 November 2023 (UTC)Reply[reply]