Talk:Fluorescein

message: 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)
replies: text: 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)
thread_title:  what causes fluorescence? 

message: 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)
thread_title:  SMILES 

message: 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)
thread_title:  different abs and em peak positions 

message: 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 71.59.70.21 (talk) 21:41, 17 March 2007 (UTC)
replies: text: I was also missing information about that, good point. 141.84.139.181
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)
thread_title:  Toxicity? 

message: 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)
thread_title:  2',7' Fluorescein Derivatives 

message: 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)
thread_title:  Published Synthetic Procedures for Fluorescein and FITC 

message: 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)
thread_title:  As an additive 

message: 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 152.77.24.38 (talk) 09:12, 22 August 2012 (UTC)
thread_title: Fluorescein "absorption" spectrum

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thread_title:  External links modified 

message: 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?
35.8.27.21 (talk) 12:10, 25 September 2018 (UTC)
replies: text: 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)
thread_title:  Pictures on this page differ 

message: 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)
thread_title:  Use by plumbers