Annihilation upconversion in ambient atmosphere
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| License | CC Attribution - NoDerivatives 4.0 International: You are free to use, copy, distribute and transmit the work or content in unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
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Transcript: English(auto-generated)
00:09
Hello, my name is Stanislav Beloushev, I am a project leader in the group from Professor Katerina Langfester, Max Planck Institute for Polymer Research in Mainz, Germany. Triplet-triplet annihilation photon energy upconversion.
00:23
Behind these high scientific words, the fascinating interplay between the organic chemistry and the soft-matter photophysics of dense populated organic triplet state is covered. With other words, upconversion, this is a physical process where the emission photons
00:44
is strongly blue-sheeted regarding the excitation photons, or the emission photons has energy which is uphill regarding the excitation photon. There are many processes in which you can observe upconversion,
01:00
for instance, sequential photon absorption or two-photon absorption or second harmonic generation. What is crucial for this process is that always you need a virtual state like in two-photon absorption process or two visual states like in second harmonic generation. For using virtual states you have to pay with excitation intensity.
01:21
That means you need watt, megawatt per square centimeter excitation intensity and also the spectral power density of your optical source must be huge, that means watt per nanometer. And the last, but not the least point, that definitely you need a coherent light. And what about the Sun? Sun is non-coherent light source,
01:43
the spectral power density is in order of 100 micro watts per nanometer and the excitation intensity on one Sun is on the level of 100 milliwatt per square centimeter air mass 1.5. And how the process of triplet-triplet annihilation upconversion works will be explained from my colleague Dr. Christian Von Haas.
02:04
Hello, my name is Dr. Christian Von Haas, I'm a postdoc in the group of Katarina Landfester and I'm explaining you the triplet-triplet annihilation upconversion process. Triplet-triplet annihilation upconversion describes the interaction of two organic molecules with different photophysical and chemical properties called sensitizer and imager.
02:24
The sensitizer is a metalated microcycle with a very high intersystem crossing rate and therefore known to be strongly phosphorescent. In contrast, the intersystem crossing rate of the imager, mostly an aromatic hydrocarbon, approaches zero. In consequence, the fluorescence quantum yields of the imager molecules are higher than 90%.
02:45
The question is, what happens if you mix such different molecules? The usage of an energy scheme will help to explain the important steps of the upconversion process. It starts with the optical excitation of the sensitizer by absorption of one single photon,
03:01
which means excitation of the ground state to the first excited singlet state. But, due to the fact that the intersystem crossing rate is almost unity, the long-living triplet state of the sensitizer populated very fast, let's say within several nanoseconds. Up to this point, we are still in the field of the classical photophysics.
03:21
Let's come to the part of the imager molecules, which are also part of the system. The triplet state of the imager is overlapping with the triplet state of the sensitizer. The energy is still stored in the triplet state of the sensitizer. It is now transferred to the triplet state of the imager. This process is called triplet-triplet energy transfer.
03:41
In the triplet state of the imager, no intersystem crossing takes place, so the energy could not be lost easily. In summary, highly populated long-living triplet states are created by means of the absorption of single photons. The next step in the story is the process of the triplet-triplet annihilation. If two emitters populated in the triplet state interact, they exchange energy.
04:03
One emitter molecule relaxes to the ground state, while the second one collects the whole energy and is lifted up into the first excited singlet state. In the classical photophysics, this state is only reached by excitation with high energy photons. By relaxation from the excited singlet state to the ground state, we obtain the delayed upconversion fluorescence.
04:27
Finally, we detect the emission of one photon of high energy respectively blue or green light, after the absorption of two photons of lower energy respectively red or near-infrared light. Let's discuss about one problem of the upconversion process, oxygen.
04:46
If the oxygen is in the system, the energy cannot be transferred from the sensitizer to the imager. The energy from the sensitizer is taken up by the oxygen, so the upconversion process is completely quenched.
05:00
To solve this crucial problem of oxygen quenching, we investigated a new media where the triplet-triplet annihilation upconversion process can take place. My name is Frederick Womm, I'm a project leader at the Max Planck Institute, and this is Filippo Marsico, one of my PhD students. And as Christian just mentioned, that oxygen is a big problem in the upconversion,
05:20
we cannot perform the reaction in open air. We have developed a general protocol for the synthesis of oxygen scavenging matrices, which are typically based on simple organic esters of inorganic acids, just as sulfuric or phosphoric acid, having carbon-carbon double bonds, which are precisely placed in these structures,
05:41
and Filippo is now going to present us an experiment how to synthesize these matrices. Now I'm going to synthesize one of our oxygen scavenger matrices by using, in this case, the chemistry based on phosphorous. Direction occurs quite under melt conditions
06:01
by using the appropriate alcohol, a base and dry condition. Now I'm going to place in the dropping funnel a functional oxychloride.
06:50
So here the liquid is ready and we can go up together upstairs for the laser measurements. A possible application for the triplet-triplet annihilation photon energy upconversion.
07:03
The materials, which were demonstrated in the chemical lab, now are prepared in a glass sandwich with a thickness of 400 micrometer. We have a scanning laser machine with a Galvo scanner and 20 mW intensity of the laser beam, and we have the new upconversion display,
07:22
which has no problem with the quenching by oxygen. Enjoy!
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