# Tag Info

29

Klaus Warzecha's answer pretty much answers your question. But I know that this subject is easier to understand if supported by some pictures. That's why I will take the same route as Klaus at explaining the concept behind why the absorption in conjugated systems is shifted to higher wavelengths but I will provide some pictures on the way. In a conjugated ...

26

It is possible, but impractical. You can "upconvert" light. This effect, as Wikipedia relays, is due to the sequential absorption of two photons per emitted photon. This is certainly possible to make in a fluorescent / phosphorescent light scenario, but the engineering challenges (or, more specifically - the cost) involved in such a solution would be steep. ...

18

Yes it is possible for molecules to absorb a single photon at a longer wavelengths than some of those that they emit at. If the molecules are thermally isolated from their surroundings then the result is that these molecules will be cooled. The effect is, however, small. The effect is caused when the fluorescence and absorption spectra overlap to a ...

17

Absorption of a photon typically results in a vibrationally excited higher electronic state of the same multiplicity. $$\ce{S_0 ->[h\nu_\mathrm{ex}] S_1}$$ In most cases, the excited state deactivates through internal conversion in a radiationless process via vibrational energy exchange with solvent molecules. No light is emitted here, but the ...

17

Yes, it is all about the absorption of light at specific wavelength. Azobenzene, the parent compound has an absorption maximum around $\lambda$= 430 nm in the visible spectrum. The interesting part is: The absorption can be tuned by substitution of the arenes. This is done before the azo coupling. Some examples are Allura Red (1), Chrysoine Resorcinol (2),...

12

Rose bengal (pictured below) is a member of the fluorescein family. (image source: wikipedia) There are 3 steps in the process where rose bengal sensitizes the formation of singlet oxygen.. \begin{gather} \ce{RB ->[$h\nu$]\ ^1RB}\tag1\\ \ce{^1RB ->T[ISC]\ ^3RB}\tag2\\ \ce{^3RB + ^3O2 ->T[sensitization]\ ^1RB + ^1O2}\tag3\\ \end{gather} In the ...

12

[...] 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 oxidation at the thiazole ring, an oxetanone is formed. This four-membered ring breaks, releases carbon dioxide and turns the thiazole into a thiazolone. The resulting ...

12

Conversion of D to L isomer or vice versa is about the last thing to worry about in this situation, even if it may be facilitated by sunlight to a significant extent (which I doubt). Also, storage of chemicals in dark coloured bottles is by no means limited to compounds that have optical isomers, or even to drugs in general. Other examples are numerous; ...

11

What is the origin of colours? Most of the colours that we perceive are originate by the selective absorption of some spectral bands and the reflection of the others wavelength, some times with the contribution of fluorescence from the absorption at a higher wavelength. If we exclude colour due to interference (e.g. some butterfly wings!) all the other ...

11

are there other classes of compounds responsible for the red and yellow colors found in flowers? Interest in colors, specifically dyes, was a real motivator for serious chemical work. Some of the early efforts were aiming to mimic Tyrian purple, also known as Royal Purple, because in antiquity it was worth its weight in gold. Two classes of molecules come ...

11

Admittedly, I'm having a professional photochemical bias when it comes to the generation of singlet oxygen! A rather safe and simple approach - even in home experiments - is the use of air, sunlight and a sensitizer (rose bengal, methylene blue, or even chlorophyll from natural resources, such as Spirulina). Here, the sensitizer is irradiated and excited ...

11

Isomerism is only one (and probably a minor) pathway. Many substances have chromophores that absorb light. Absorption leads to a high energy intermediate that is more reactive and able to access degradation pathways that were unavailable from the ground state. This is different from thermal excitation because the energizing photon carries a lot more energy ...

10

The image shows the absorption and emission spektra of molecules. For isolated atoms, you would indeed observe sharp lines. Think in the Fraunhofer lines. UV/VIS absorption of molecules In the case of molecules, absorption occurs from the vibrationally relaxed electronic ground state ($S_0$) to various vibration levels of the electronically excited $S_1$ ...

10

The effect is already "visible" on the comparison of ethene ($\ce{H2C=CH2}$) and 1,3-butadiene ($\ce{H2C=CH-CH=CH2}$). Let's build butadiene by combination of the molecular orbitals (MOs) of of ethene. Combination of the $\pi$ orbitals gives one new occupied MO without a nodal plane (this is lower in energy than the $\pi$ orbital of ethene) and another ...

10

Even if the UV light idea doesn't work out very well I still want a way to do this With some photochemical background, I suggest to forget about running such a UV lamp Remember that your plasma will be formed in air. For every molecule of ozone formed, there are much more harm- and odourless $\ce{O2}$ molecules around. If you cleave $\ce{O3}$ \[\ce{O3 + ...

10

You're right that ground state $\ce{^3O2}$ doesn't undergo this reaction. There is no direct excitation of oxygen either. The key in these processes is the electronic excitation of tetraphenyl porphyrine (TPP). The excited singlet state of the dye undergoes intersystem crossing to a triplet state. The latter interacts with ground state oxygen and generates ...

9

The spontaneous emission of light by a substance not resulting from heat is luminescence (a type of cold-body radiation). $\ce{^1}$ A few types of luminescence are: Bioluminescence: Made by living creatures such as fireflies, glow-worms, and many marine creatures. Chemoluminescence: made by a chemical reaction. Glow sticks work this way. ...

9

The obvious Star Wars puns aside, I have never heard about the dianion of a carbon dioxide dianion and/or that it was named carbonite. However, the carbon dioxide radical anion, $\ce{CO2^{.-}}$, is experimentally available. Typically, it is generated by hydrogen atom abstraction from formate, $\ce{HCOO-}$, using $\ce{HO^.}$ radicals. The $\ce{HO^.}$ ...

8

In the production of white paper, the bleached pulp is often treated with optical brightening additives (OBA), that absorb in the uv and emit in the blue range. If I remember correctly, a typical example is 4,4'-diaminostilbene-2,2'-disulfonic acid. Here's an article from The Open Textile journal (OA) in which the compound mentioned above is used as a ...

8

Let's have an extreme example of 9 conjugated double bonds. That makes your $\pi$ HOMO orbital. The LUMO, $\pi^\star$, has one node, the middle double bond being antibonding, so it will consist of two times 4 conjugated $\pi$ bonds. To say, the difference in energy between HOMO and LUMO is quite small, therefore the excitation energy is low.

8

Consider that when $1$ molecule of glucose forms, this happens at the cost of $6$ molecules of $\ce{CO2}$ and $6$ molecules of $\ce{H2O}$ : $\ce{6CO2(g) + 6H2O(l) -> C6H12O6(s) + 6O2(g)}$ Considering that at $25\ \mathrm{^\circ C}$ and $1\ \text{atm}$ $\Delta H_{\text{f},\ce{CO2}}^\circ=-393.5\ \text{kJ/mol}$ $\Delta H_{\text{f},\ce{H2O}}^\circ=... 8 The key issue here that we are comparing excited states. So let's begin by defining Singlet and Triplet Excited States. Singlet and Triplet Excited States: A singlet or a triplet can form when one electron is excited to a higher energy level. In an excited singlet state, the electron is promoted in the same spin orientation as it was in the ground state (... 8 I see a couple of problems here: Beam diameter vs volume of the beverage The volume of the sample that is actually hit by a narrow laser beam is very small, as compared to the total volume of the sample (= the drink). As a consequence, only a very small amount of the dye in drink will undergo a transformation. A wide beam of a switchable light source ... 8 Rigidity is definitely an important factor. At$295\ \mathrm{K}$, indeno[2,1-a] has a fluorescence quantum yield$\Phi_F$of 0.94, (DOI). In an organic glass at$77\ \mathrm{K}$, even (E)-stilbene, which hardly shows any fluorescence at room temperature, exhibits a$\Phi_F$of 0.75. Vibrational stretching of$\ce{C-C}$bonds in substituents can ... 8 Azobenzenes are one of the most widely used moietes in photochemically switchable systems. Nevertheless, the pathways for the E-Z isomerisation of azobenzene in the$S_1$and the$S_2$state have been in debate for decades and I'm not quite sure whether this is finally solved. However, in the$n \rightarrow \pi^*$excited state ($S_1$), the rotation is ... 8 Such materials not only exist but are common Most people will have seen an actual demonstration of materials that exploit the phenomenon of a substance that absorbs NIR light and emits visible light. Most Green laser-pointers are based on their use. These usually rely on a semiconductor laser outputting near-infra-red (NIR) light at 1063nm wavelength ... 7 I would say it would be much easier to try to keep the area oxygen free. Atomic oxygen (i.e.$\ce{O}$) is a highly reactive radical. This would react either with another$\ce{O}$, or an$\ce{O_2}$. It is hard to avoid this unless you can get rid of the$\ce{O_2}$. Not sure what kind of a geometry you are thinking of, but purging the volume with$\ce{N_2}\$ ...

7

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 released with an emitted photon must previously have been added into the molecule (or atom) in question. For example, if singlet oxygen is created chemically, it ...

7

There are indeed: we use them in "Laser Viewing Cards" to be able to see IR Laser. An example of such a card is presented below: When illuminated with IR light, it emits visible light. The principle is that the molecule are trapped in an excited state that requires an IR photon to de-excite. These cards need prior charging but it last several hours.

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