Spin, Exciton and Chemical Dynamics in Crystalline Solids

晶体固体中的自旋、激子和化学动力学

• 批准号: 2154210
• 负责人: Miguel Garcia-Garibay
• 金额: $ 60万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-15 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2154210&HistoricalAwards=false
• 关键词: Spin; Exciton; Chemical; Dynamics; Crystalline

With support from the Chemical Structure, Dynamic & Mechanism B Program of the NSF Chemistry Division, Professor Miguel A. Garcia-Garibay of the Department of Chemistry and Biochemistry at UCLA will investigate the use of light and crystals to explore a new platform for Quantum Information Science (QIS). Crystals make it possible to design chemical processes and reactions that cannot occur in liquids or in gases. They open the door for a deeper understanding of reaction mechanisms and for the exploration and design of solvent-free synthesis and applications in materials science. While molecules in crystals do not have the freedom of motion that is expected for chemical reactions to take place, reactions in crystals can be engineered in a reliable manner by taking advantage of a strategy used by nature based on biological structures that can capture and guide the energy contained in sunlight. Examples of such sunlight-induced, or “photobiological” processes include photosynthesis, DNA repair, and the biological compasses used by birds to guide their navigation across the planet. Similar to those systems, reactions in crystals rely on the capture of light to generate excited states that go on to form highly reactive intermediates, whose fate is controlled by the crystal’s rigidity, homogeneity, and order. Pulsed lasers aimed at selected crystalline ketones will be used to generate relatively long-lived magnetic species known as “triplet radical pairs”. These consist of two extremely close unpaired electrons formed by the cleavage of a single chemical bond, which causes their magnetic spins to be strongly entangled and be relatively impervious to external magnetic perturbations. These characteristics endow them with great potential for applications in Quantum Information Science (QIS). The second part of this project explores a relatively exotic type of chemical reaction where a single light particle, or “photon”, leads to many chemical events. These so-called quantum chain reactions are enabled by the strong energetic interactions between neighboring molecules, which lead to the transformation of photons into “excitons” and are helped by reactants that contain and unleash large amounts of energy. The third objective of this project is to provide a multi-disciplinary training ground for students who will contribute to the intellectual and human infrastructure needed to support our country’s academic and industrial enterprises. The PI will lead the annual UCLA Physical Sciences Fair, “Exploring your Universe,” which attracts ca. 7,000-10,000 visitors to campus, and group members will have a booth to share with the public the exciting things that can be done with crystals and light.The Garcia-Garibay group has established the structural and energetic requirements needed to engineer a number of photochemical reactions in the crystalline solid state. For the intellectual merit of this project, they will take advantage of nanocrystals (ca. 200 nm) suspended in water in order to detect the absorption spectra and decay kinetics of triplet excited states and triplet radical pairs to explore two photochemical processes that can only occur in crystalline solids: (1) the chemical and spin dynamics of highly entangled triplet radical pairs as a potential platform for quantum information science (QIS), and (2) the potential of quantum chain reactions with triplet chain carriers as a powerful signal amplification mechanism. With triplet excitons providing efficient energy delocalization mechanisms, these reactions are expected to reach chain lengths with as many as 106-109 reactions per photon absorbed, depending on the lifetime of the triplet excited states. For the first part, they take advantage of a series of 1,1-diphenyl-2-propanones and 1,1,1-triphenyl-2-propanones with a variety of substituents at C3 to study the kinetics of intersystem crossing of triplet radical pairs. While ketones with radical stabilizing substituents at C3 are known to lose CO to form triplet alkyl-alkyl radical pairs that go on to give products from a radical-radical combination reactions, ketones with high C2-C3 bond dissociation energies can only undergo an alpha-cleavage of the C1-C2 bond to form triplet acyl-alky radical pairs. These intermediates go back to the starting material after intersystem crossing to the corresponding singlet acyl-alkyl radical pairs. Much of what it is known about intersystem crossing in radical pairs comes from experiments where long inter-radical distances lead to weak exchange interactions with dominant hyperfine coupling (hfc) intersystem crossing mechanisms. By contrast, radical pairs in crystalline solids offer the opportunity to explore a new frontier: one where rigid radicals are highly entangled as a result of a very large singlet-triplet gap. Long triplet lifetimes are observed despite having the two electrons within van der Waals distance as the result of (a) inefficient hfc, (b) unfavorable geometries for spin-orbit coupling (SOC), and (c) spin-lattice relaxation slowed down by crystal rigidity. Long-lived entanglements makes these crystal-trapped radical pairs excellent qubit pair candidates for applications in quantum information science. For the exploration of a triplet exciton-enabled quantum chain reaction, this research will study solid state reactivity of crystalline sensitized Dewar benzenes. These are known to undergo an efficient triplet state adiabatic reaction where the triplet state Hückel benzene photoproduct is a competent energy donor that can carry out a quantum chain. Altogether, the work covered by this project is expected to improve basic understanding of reaction mechanisms and chemical reactivity in rigid materials and provide students the opportunity to receive a highly interdisciplinary training.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在美国国家科学基金会化学部化学结构、动态和机制B项目的支持下，加州大学洛杉矶分校化学和生物化学系的Miguel a . Garcia-Garibay教授将研究光和晶体的使用，以探索量子信息科学（QIS）的新平台。晶体使设计不能在液体或气体中发生的化学过程和反应成为可能。它们为更深入地了解反应机制以及探索和设计无溶剂合成及其在材料科学中的应用打开了大门。虽然晶体中的分子不具有化学反应发生时所期望的运动自由，但晶体中的反应可以通过利用基于自然的生物结构的策略以可靠的方式进行设计，这种策略可以捕获和引导阳光中所含的能量。这种由阳光引起的或“光生物学”过程的例子包括光合作用、DNA修复和鸟类用来引导它们在地球上导航的生物指南针。与这些系统类似，晶体中的反应依赖于光的捕获来产生激发态，这些激发态继续形成高活性的中间体，其命运由晶体的刚性、均匀性和有序性控制。脉冲激光瞄准选定的晶体酮将被用来产生寿命相对较长的磁性物质，称为“三联体自由基对”。它们由两个非常接近的未配对电子组成，这些电子是由单个化学键的裂解形成的，这导致它们的磁自旋强烈纠缠，并且相对不受外部磁扰动的影响。这些特性赋予了它们在量子信息科学（QIS）中的巨大应用潜力。该项目的第二部分探索了一种相对奇特的化学反应类型，其中单个光粒子或“光子”导致许多化学事件。这些所谓的量子链式反应是由相邻分子之间的强能量相互作用实现的，这种相互作用导致光子转化为“激子”，并在含有和释放大量能量的反应物的帮助下实现。该项目的第三个目标是为学生提供一个多学科的培训基地，这些学生将为支持我国的学术和工业企业所需的智力和人力基础设施作出贡献。PI将领导一年一度的加州大学洛杉矶分校物理科学博览会，“探索你的宇宙”，吸引大约7,000-10,000名游客到校园，小组成员将有一个展位与公众分享可以用晶体和光做的令人兴奋的事情。Garcia-Garibay小组已经建立了在晶体固体状态下设计许多光化学反应所需的结构和能量要求。为了这个项目的智力价值，他们将利用悬浮在水中的纳米晶体（约200纳米）来检测三重态激发态和三重态自由基对的吸收光谱和衰变动力学，以探索两种只能发生在晶体固体中的光化学过程：(1)高度纠缠的三重态自由基对的化学和自旋动力学作为量子信息科学（QIS）的潜在平台；(2)三重态链载体作为强大信号放大机制的量子链式反应的潜力。由于三重态激子提供了有效的能量离域机制，这些反应有望达到链长，每个光子吸收多达106-109个反应，这取决于三重态激发态的寿命。在第一部分中，他们利用一系列1,1-二苯基-2-丙烷和1,1,1-三苯基-2-丙烷在C3上具有多种取代基来研究三重态自由基对的系统间交叉动力学。在C3上具有稳定自由基取代基的酮会失去CO，形成三联体烷基-烷基自由基对，并在自由基-自由基结合反应中生成产物，而具有高C2-C3键解离能的酮只能经历C1-C2键的α -裂解，形成三联体烷基-烷基自由基对。这些中间体在系统间交叉成相应的单线态酰基-烷基自由基对后回到起始物质。关于自由基对的系统间交叉的大部分知识来自于实验，在实验中，较长的自由基间距离导致弱交换相互作用与主导的超精细耦合（hfc）系统间交叉机制。相比之下，晶体固体中的自由基对提供了探索新领域的机会：由于非常大的单重态-三重态间隙，刚性自由基高度纠缠。由于(a)低效率的hfc， (b)自旋-轨道耦合（SOC）的不利几何形状，以及(c)自旋-晶格弛豫被晶体刚性减慢，尽管两个电子处于范德华距离内，但仍观察到较长的三重态寿命。长寿命的纠缠使这些晶体捕获的基对成为量子信息科学应用的优秀量子比特对候选者。为了探索三重态激子激活的量子链反应，本研究将研究晶体敏化杜瓦苯的固态反应性。已知它们可以进行有效的三重态绝热反应，其中三重态h<s:1>克尔苯光产物是可以进行量子链的合格能量供体。总而言之，本项目所涵盖的工作有望提高对刚性材料的反应机制和化学反应性的基本理解，并为学生提供接受高度跨学科培训的机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Kinetics of Photoreactive 4,4′-Dimethylbenzophenone Nanocrystals: Relative Contributions to Triplet Decay from Intermolecular H-Atom Transfer and Reductive Charge Transfer Quenching

光反应性 4,4-二甲基二苯甲酮纳米晶体的动力学：分子间氢原子转移和还原电荷转移猝灭对三重态衰变的相对贡献

• DOI: 10.1021/acs.jpca.3c03828
• 发表时间: 2023
• 期刊: The Journal of Physical Chemistry A
• 作者: King, Jared;Garcia-Garibay, Miguel A.
• 通讯作者: Garcia-Garibay, Miguel A.

Reaction amplification with a gain: Triplet exciton–mediated quantum chain using mixed crystals with a tailor-made triplet sensitizer

带增益的反应放大：使用带有定制三重态敏化剂的混合晶体的三重态激子介导的量子链

• DOI: 10.1073/pnas.2401982121
• 发表时间: 2024
• 期刊: Proceedings of the National Academy of Sciences
• 作者: Paul, Indrajit;Konieczny, Krzysztof A.;Chavez, Roberto;Garcia-Garibay, Miguel A.
• 通讯作者: Garcia-Garibay, Miguel A.

Exceptionally Long Lifetimes of Strongly Entangled Acyl–Trityl Radical Pairs Photochemically Generated in Crystalline Trityl Ketones

结晶三苯甲基酮中光化学产生的强缠结酰基-三苯甲基自由基对的寿命极长

• DOI: 10.1021/jacs.2c11787
• 发表时间: 2023
• 期刊: Journal of the American Chemical Society
• 影响因子: 15
• 作者: Hipwell, Vince M.;Meyer, Alana Rose;Garcia-Garibay, Miguel A.
• 通讯作者: Garcia-Garibay, Miguel A.