13
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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 ...
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12
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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 ...
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11
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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 ...
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11
votes
Accepted
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 ...
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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 ...
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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 ...
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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,...
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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......
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7
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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 ...
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7
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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 ...
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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 ...
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6
votes
Accepted
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 ...
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6
votes
Accepted
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 ...
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6
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What are some compounds that do fluorescence but not phosphorescence, phosphorescence but not fluorescence, and 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 ...
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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\...
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5
votes
Accepted
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 ...
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5
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 ...
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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 ...
4
votes
Accepted
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 ...
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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. ...
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4
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 ...
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4
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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 ...
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4
votes
Excited states and emission lifetimes
Thanks @Achem and @porphyrin for your comments. I do not know if an Answer is the right format for this Comment but the comments do not allow enough character to develop my argument.
I think we are ...
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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 ...
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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 ...
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3
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 ...
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3
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 ...
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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 ...
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3
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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 ...
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3
votes
Fluorescence: what mechanism regulates the rate of discharge of energy?
The after-glow is called phosphorescence. Fluorescence stops immediately the moment light is turned off because the process is ultrafast!
Phosphorescence on the other hand requires a change in the ...
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