QnAs with Miguel A. Garcia-Garibay
Miguel Garcia-Garibay has made many advances in the field of physical organic chemistry, with a particular focus on the organic chemistry of crystalline solids. Among his many contributions to the field is the term “amphidynamic crystals,” and he has led the way in the study of this class of condensed phase matter that combines crystalline lattice-forming elements and dynamic parts. Now a professor of chemistry and biochemistry at the University of California, Los Angeles, Garcia-Garibay was elected to the National Academy of Sciences in 2023. In his Inaugural Article, Garcia-Garibay describes recent advances in using mixed crystalline materials for chemical amplification of photons with high quantum yield (1).
PNAS:
How did you become interested in the chemical amplification of photons in a crystalline solid?
Garcia-Garibay: This paper represents the evolution of work going on in our group for about 15 years. We had an opportunity to look at what we call a quantum chain reaction on a system that was quite controversial in the literature. One way to test the controversy was to demonstrate that a quantum chain reaction could occur. This is a system where a molecule can be excited and then it reacts in the excited state so that you end up with an excited product, and then that product can transfer excitation to a new reactant molecule so that it becomes like a domino effect.
What we found… was that the time scale for the reaction and the lifetime of the excited state [were] extremely short, on the order of about 6 picoseconds, which is about six-billionth of a second. So a quantum chain reaction couldn’t be shown because 6 picoseconds is not enough time to transfer energy from one product molecule to a reactant molecule. What we then decided to do based on our expertise is to do this in a crystalline solid, where molecules pack close together and energy transfer is known to be extremely fast.
PNAS:
What did you find?
Garcia-Garibay: In some preliminary work, we were able to show that this reaction indeed occurs—where the excited state reactant goes into the excited state product that in the crystal is able to transfer energy to another molecule and set up a chain reaction. One of the limitations of that work was that because the excited state was so short, there were a limited number of transfers, so the length of the chain was very small, somewhere between three to maybe 10 to 12 molecules per photon.
In the Inaugural Article, we decided to look for a system where now the excited state would be much, much longer lived. We were looking for something that would live at least a few microseconds, and this paper represents the execution of that idea, to have an opportunity to have this quantum chain reaction with many, many more events occurring per photon. Most interactions between matter and light involve one photon for one event. In this particular case, we can amplify the effects of one photon many-fold, and we’re reporting in this paper over 500 reactions per photon absorbed.
PNAS:
How did you achieve this?
Garcia-Garibay: The necessary design element was to create a crystal where we have the reactant that is going to demonstrate this amplification process and have an antenna molecule that would be responsible for absorbing the light and starting the chain reaction. It is what we call a “tailormade” sensitizer, so this particular antenna would nicely fit into the crystal lattice of the reactant. In our current design, we also selected a molecule that exists in what is called a triplet excited state, which is an excited state that is relatively long-lived.
PNAS:
What are some of the applications of this work?
Garcia-Garibay: We think that we will be able to adapt the principles of this chain reaction to amplify signals, for instance in detectors such as those used for high-energy particle physics. By tweaking the system, we might be able to improve the detection of particles that are captured from cosmic, solar, and other types of radiation. We think that it can be used to also increase the sensitivity of sensors. If you develop a sensor where you can have one photon translating to hundreds or perhaps even thousands of events, then you really have an opportunity to amplify very rare events. It could also have applications in biological systems.
PNAS:
What follow-up experiments do you plan to do?
Garcia-Garibay: From this study, we learned that the limitation really is the lifetime of the excited state product, so we will be looking for systems where the excited state product has longer lifetimes. In this particular example, our excited state product has a lifetime on the order of about 1 microsecond. We know chemical systems where the excited state lifetime can extend into the millisecond and second time scales. We believe that there is an opportunity to amplify the chain by perhaps up to six orders of magnitude or more, so we might be able to get more than 1 million reactions per incident photon.
PNAS:
What were some challenges you faced in this work?
Garcia-Garibay: The primary challenge is that we’re looking at chemical reactions in crystalline solids, which is the area of expertise of my group. While chemistry has been extensively developed in the gas phase and in liquids, chemical reactions in solids remain one of the frontiers of chemical reactivity. We’ve been making progress in the understanding of what types of molecules will crystallize and react in the crystalline state. One of the main challenges is to understand and develop the rules of these chemical reactions that can happen in the solid state.
PNAS:
What was your takeaway from this project?
Garcia-Garibay: For me, personally, the takeaway is that chemistry continues giving us opportunities to look to new directions to explore and develop. There is a sense that we already know a lot…but I think there are still things out there that remain to be discovered.
Reference
1
I. Paul, K. A. Konieczny, R. Chavez, M. A. Garcia-Garibay, Reaction amplification with a gain by a triplet exciton-mediated quantum chain using a tailor-made triplet sensitizer in mixed crystals of a dewar benzene. Proc. Natl. Acad. Sci. U.S.A. 121, e2401982121 (2024).
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© 2023. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Submission history
Published online: April 3, 2024
Published in issue: April 9, 2024
Notes
This is a QnAs with a member of the National Academy of Sciences to accompany the member’s Inaugural Article, e2401982121 in vol. 121, issue 14.
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QnAs with Miguel A. Garcia-Garibay, Proc. Natl. Acad. Sci. U.S.A.
121 (15) e2404940121,
https://doi.org/10.1073/pnas.2404940121
(2024).
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