13 votes

How does molecular structure contribute in the property of fluorescence?

Keep in mind a few things that must happen for an absorption process to result in fluorescence: (1) the initial transition is to an excited electronic state that observes certain rules regarding the ...
Buck Thorn's user avatar
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12 votes

What is special about the molecule luciferin that it can emit light?

[...] the protein luciferin is oxidized by the enzyme luciferase Luciferin is not a protein, but a benzothiazole with a thiazole attached to the carbon atom between nitrogen an sulfur. Upon ...
Klaus-Dieter Warzecha's user avatar
11 votes

Why do glow-in-the-dark substances dim gradually?

There are two potential questions here: one is why is dimming a slow drawn-out process (incoherent, unlike a "switch"). The second question is why different stars may appear to lose their intensity at ...
Buck Thorn's user avatar
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10 votes
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Lifetime components in phosphorescence decay

Phosphorescence should be at a longer wavelength than any fluorescence so carefully using a filter or grating should remove any fluorescence. Also measuring at different wavelengths will change ...
porphyrin's user avatar
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9 votes
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Why do different substances containing saturated hydrocarbons burns with different flame?

LPG is propane, butane or a mixture of both. Paraffin candle wax is $(CH_2)_n$ typically $C_{31}H_{64}$ (other, nonparaffin, waxes are also used in candles, like stearin, beeswax, etc.) However, LPG ...
James Gaidis's user avatar
9 votes
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Why is collagen fibre autofluorescent?

Two proteins, collagen and elastin, are giving autofluorescence and both have a Pyridinoline compound as a cross linker, deoxypyridinoline in collagen and desmosine in elastin: Thus, these two ...
Mathew Mahindaratne's user avatar
8 votes
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Why are glow-in-the-dark things usually green?

The human eye is most sensitive in green wavelengths. Therefore, if one were to put the same amount of light energy into different wavelengths, the green portion of the spectrum would appear brightest,...
DrMoishe Pippik's user avatar
7 votes

What is special about the molecule luciferin that it can emit light?

Klaus gave a nice summary on luciferin. The second part of your question was: Also, are there any chemical reactions which produce high energy electromagnetic waves, such as X-Rays? Any energy ...
Jan's user avatar
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7 votes
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Is it right to say that fluorescent lamps are actually fluorescent?

Fluorescent lamps do primarily work by fluorescence. According to this Wikipedia article: "The inner surface of the lamp is coated with a fluorescent (and often slightly phosphorescent) coating......
airhuff's user avatar
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7 votes

Absorption and emission at same wavelength?

Yes it is very common particularly in the more rigid type of molecule. The best example is chlorophyll and this overlap of absorption and emission leads to energy transfer in photosynthesis. The ...
porphyrin's user avatar
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7 votes

Why do different substances containing saturated hydrocarbons burns with different flame?

I have read some answers on web which says that it is due to the insufficient supply of oxygen, so I tried burning candle beside LPG ( so there is no difference in supply of oxygen for both candle and ...
AChem's user avatar
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7 votes

Compounds with fluorescence and/or phosphorescence, what can do both?

An excited state has initially five possible fates, (1) internal conversion to a state of the same spin, (2) intersystem crossing to a state of different spin (e.g. singlet to triplet) (3) emission to ...
porphyrin's user avatar
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6 votes
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Nitrogen dioxide fluorescence quenching and lifetime

You are looking for the rate constant $1/\tau^0=k_2$. The rate equation for the $\ce{NO2^*}$ is (using $N^*$ for $\ce{[NO2^*]}$ and N for ground state NO2), $\displaystyle \frac{dN^*}{dt}=-k_2N^*$ and ...
porphyrin's user avatar
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6 votes
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Is the XRF spectroscopy equally sensitive for every element?

In a very very broad reasoning, XRF is much more sensitive to the "mid-range" elements. Elements below Na are generally not detectable. The x-ray tubes must have a beryllium window to seal the ...
MaxW's user avatar
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5 votes
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What makes scorpions glow under UV light?

As mentioned in this comment, which links to this paper, and this comment, which links to this Wired article, there are at least two molecules: $\beta$-carboline: 4-methyl-7-hydroxycoumarin: $\tiny\...
pentavalentcarbon's user avatar
5 votes
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Deriving fluorescence intensity equations

Concentrating on fluorescence intensity for the moment the equation becomes $I_O = I_D $ where $I_O$ is that for the free dye and $I_D$ for that bound to the DNA. If $\alpha$ dissociates the ...
porphyrin's user avatar
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5 votes
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Why do some molecules show non-symmetric absorption and emission bands?

Mirror image spectra are only observed in solution and then only if the ground and excited state potential energies have almost exactly the same shape. Thus in rigid molecules such as anthracene a ...
porphyrin's user avatar
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5 votes

What chemical(s) in peanut butter cause it to glow under UV light?

Many natural oils from vegetable sources show intense fluorescence under UV. Olive oil glows brilliant red under UV. In the peanut butter case, my first guess was turmeric, the yellow spice, because ...
AChem's user avatar
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4 votes

What makes a species "fluorescence quencher"?

A fluorescence quencher is any species that causes your fluorophore to stop fluorescing. There are several ways this can happen, but there are two broad categories: chemical reactions and energy ...
Ben Norris's user avatar
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4 votes
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Why does aqeous fluorescein shine when exposed to UV light?

The process is called fluorescence. Some substances, such as calcium sulfide, $\ce{CaS}$, absorb light and release it slowly in a process called phosphorescence, glowing for some time after the source ...
DrMoishe Pippik's user avatar
4 votes
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Why do glow-in-the-dark substances dim gradually?

Source of light I imagine that the cause of the stars becoming dimmer is that some electrons are relaxing down before others. This statement could be interpreted in two different ways, one ...
Karsten's user avatar
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4 votes

How to calculate molecular emission spectra?

As you mentioned, Gaussian can do it but is proprietary. I believe ezSpectrum (https://github.com/iopenshell/ezSpectrum) might be able to do what you are looking at but I have not used it myself so ...
Michael Banck's user avatar
4 votes

What fluorescent materials absorb visible light and emit UVC light?

If you want to convert visible light into UV, you have two options. Two-photon excited fluorescence. The process is inherently wasteful, but the field is studied due to applications in microscopy. ...
permeakra's user avatar
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4 votes

Why do different substances containing saturated hydrocarbons burns with different flame?

A propane molecule $\ce{C3H8}$ in the gas phase must find $7$ molecules $\ce{O2}$ to burn totally. A wax molecule $\ce{C_{31}H_{64}}$ must find $63$ molecules $\ce{O2}$ to burn completely. During its ...
Maurice's user avatar
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4 votes
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Excited states and emission lifetimes

Yes, singlets fluoresce and triplets phosphoresce. So the singlet lifetime is the fluorescence lifetime and is the inverse of singlet excited state decay rate constant and similarly for ...
porphyrin's user avatar
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4 votes

How are these green, blue, and purple markers fluorescing under monochromatic 589nm (yellow) light?

This is an interesting observation and one can appreciate that the OP thought about two photon absorption as a. A couple of observations first that challenge the hypothesis. Ordinary sodium lamps or ...
AChem's user avatar
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3 votes

What fluorescent materials absorb visible light and emit UVC light?

It is not possible in a single molecule as energy conservation will forbid it. There is not enough thermal energy, $k_BT \approx 210 $ wavenumbers, visible to uv thousands of wavenumbers. It is sort ...
porphyrin's user avatar
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3 votes

Measuring a high Michaelis constant using fluorescence

Based on your description, it sounds like you are measuring the production of hydrogen peroxide by an oxidase enzyme. In that case, it is not necessary for the Amplex Red to be at the same ...
Andrew's user avatar
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3 votes
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Are there any (simple) molecules with very different absorption and emission dipole directions?

In part of the naphthalene molecule you draw you indicate a transition moment. This is the direction for absorption into the lowest excited state $S_1$. As naphthalene is highly symmetric the ...
porphyrin's user avatar
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3 votes

Why do some molecules show non-symmetric absorption and emission bands?

From the Jablonski diagram, The mirror image is only true if you are talking about transitions from $S_0$ to $S_1$ (absorption) and $S_1$ to $S_0$. Also read about Kasha's rule. Quinine is the ...
AChem's user avatar
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