Column chromatography of a small part of the previously done reaction. The test tubes and the column looks like I’ve been purifying fluorescein if it is viewed under UV light.

With this method I am able to separate the fluorescent compound from the other compounds what are present in the reaction mixture and it will be possible to find out that what have formed in the flask yesterday. The good point is, that it is not a black gunk(:


Removing fluorescein from the organic phase. During the reaction an amide of fluorescein was made what doesn’t have a color and it does not fluoresces under these conditions. So hopefully, the transparency of the upper layer means something good.

The bottom layer is a dilute (1M) sodium hydroxide solution what reacts with the fluorescein to form the highly fluorescent fluoriescein sodium salt what produces this intense green color in the aqueous phase.

Interesting fact: the acid form of the fluorescein does not emit the characteristic intense green color under UV light, it only emits a yellowish-orange color in high concentrations.

There was a reaction what produced an intense fluorescent side product what I purified by column chromatography a week ago. After the purification I ended up with this oil what looks like this under UV light. It is simply fascinating, it looks adorable, or at least I think this about this small flask with the few mg of purified compound in it.

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Something strange happened here. The compound what I started from fluoresces with a deep green color and the compound what I am making fluoresces under UV light with a deep blue color and not this intense yellowish-green color. Conclusion: a side reaction happened and according to the TLC something went really wrong.

Let’s find out that what was produced from this reaction… I hope that nobody added some fluorescein to my reaction while I was not in the lab…


Fluorescein sodium salt and a little Rhodamine 6G in a glass tank. This is not interesting at all, the only “special” about this is that I got a flashlight for a few day from a friend and I tried it out with this. 

The flashlight is a cheap Yongnuo YN-460 (~50 USD on eBay) what also emits some UV light what produces this nice green/red fluorescence with the fluorescent dyes.

Well, when I washed the previously made red dye (what is not fluorescent at all) with some tetrahydrofuran (THF) a highly fluorescent solution was obtained what had a fluorescense almost as intense as fluorescein.

Another interesting thing was, that when I diluted this green fluorescent solution with water, the green color faded and a faint blue fluorescense could be seen under a UV lamp. 

And the third thing what is quite strange, that according to the analysis what was done with this compound, the green fluorescent thing is the same as the red dye at the top of the fritted glass funnel.


The 850.-th post on the blog is from things what never-ever gets boring: fun with fluorescent dyes!

The red color is emitted by a fairly common dye: Rhodamine B. The green color is a bit more interesting, it is emitted by merbromin, an organomercury chemical: 

External image

Merbromin is one of the best antiseptics and it is still used in several countries, but because of its mercury content, it is no longer sold in the United States, Germany, or France. When used as a topical antiseptic, it stains the skin bright red and it is quite hard to remove. Luckily it is only used as a 2% solution, or more dilute, and since it is not readily absorbed by the skin, it is perfectly safe to use.

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A solution of ditosyl erythritol under UV light. As the reaction completes the green color should fade, since it is caused by the not yet reacted ditosyl compound. 

It could be pretty useful if one of the compounds what you work with fluoresces under UV light, since it could be detected in no time with a simple UV lamp, that is is present if the reaction or not.

Two pieces of fluorite under UV light.  

Fluorite (CaF2) is naturally occurring mineral, it is the far most common and well-known fluorine containing mineral found on earth. When pure, it is completely colorless and transmits light from 200 nm what means it lets through UVA, UVB and some of the UVC photons.

But when it is contaminated with other elements, usually with yttrium, cerium, iron, sodium, barium, aluminium, ect. it could change the color of the mineal and could also cause a fluorescence under UV light, just as in this case. Originally the fluorite on the right had a green color, but it emits strong blue light under UVB.

I know, that this is not strictly chemistry, but is there anyone who would like to see some mineral related posts on the blog in the future?


Not from the lab,  but something interesting (or at least it’s interesting for me). 

I tried, that various photographic lenses how will behave under UV light and got quite interesting results. I borrowed a few lenses from a really good friend and started to do some experiments. Some of the lenses fluorescence under UV light with blue/green/yellow/ect. color. 

Why do they glow under UV? Depending on the composition of the glass, it could easily contain mixtures a few rare earth elements, usually Lanthanum, Cerium and sometimes Thorium (yes, that radioactive thing at the bottom of the periodic table). These elements are added to the glass, since if they are present, the glass has a higher refractive index what means, that better optics could be made from them, with lower chromatic aberration.

What is chromatic aberration? It’s also called achromatism or chromatic distortion, is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have different refractive indices for different wavelengths of light. The refractive index decreases with increasing wavelength. An example.

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One of the most simple tests to show an organic compound present in a reaction mixture is irradiating the sample with UV light. If you know, that the product of the reaction should fluorescence blue, while the starting materials do not emit any light after irradiating the sample with UV, could help a lot while doing a reaction. 

In this case a side product formed from the reaction above 130 °C, while the desired product formed at 100 °C. The starting material and the product did not emit any light under UV, while the side product did. So after taking the picture, I was sure, that the reaction is ready.

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Guest post:   We were working on amides with fluorescent probes attached to them. They only fluoresce when dilute as well!   Top-left: Column chromatography of reaction which is being monitored with UV, extremely easy to collect fractions! Top-Right: final product under UV. Bottom-Left:Concentrated fluorescent amide, when even more concentrated it looked like BBQ sauce! Bottom-Right: fluorescent amide in syringe ready for use!

Credit: Thomas and Sam(The Red Devil)