Understanding Excimers in Molecular J- and H-aggregates: A Holstein-Peierls Approach

了解分子 J 和 H 聚集体中的准分子：荷斯坦-佩尔斯方法

• 批准号: 2221923
• 负责人: Francis Spano
• 金额: $ 38.1万
• 依托单位: Temple University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-01 至 2026-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2221923&HistoricalAwards=false
• 关键词: Understanding; Excimers; Molecular; aggregates; Holstein

NONTECHNICAL SUMMARY This award supports theoretical/computational research and education on how light interacts with semiconductor materials made of organic molecules. The more familiar semiconductors like silicon, which is widely used in microelectronics and computer chips, are inorganic. However, semiconductors based on organic molecules offer advantages such as less expensive materials processing and more favorable mechanical properties. Organic materials continue to make inroads into commercial devices, such as organic light-emitting diodes or OLEDs used in displays (the “OLED” TV), solar cells, which convert sunlight into electrical energy, and even “wearable” electronic devices and sensors. The PI and his research team will investigate fundamental processes such as light absorption and light emission in organic crystals and aggregates, as well as how the energy from light absorption is transported between molecules - similar to what occurs in plants during the process of photosynthesis. The research team will conduct a theoretical investigation by solving equations based on quantum mechanics which describe how organic molecules respond to light. The equations will be solved using sophisticated computer algorithms. Of particular interest are certain electronic excited states known as excimers, which emit light of longer wavelengths and convert electronic energy into light energy less efficiently. The PI and his team will study how such excimers form and ultimately how to design molecular aggregates which avoid excimer formation. The proposed activities will also enhance research infrastructure through collaborations with experimentalists such as Professor Libai Huang at Purdue University, who will employ state-or-the-art experimental techniques to probe energy transport in organic films. Overall, this research effort should contribute to a blueprint for the next generation of electronic devices based on organic materials.TECHNICAL SUMMARY This award supports theoretical and computational research and education on how light is absorbed or emitted from semiconductor materials made of organic molecules. Solid phases of pi-conjugated molecules and polymers continue to receive widespread attention as semiconducting materials in field effect transistors, light emitting diodes, and solar cells. However, despite the more than five decades of intensive experimental and theoretical research following Kasha's pioneering work on molecular H- and J-aggregates, important questions remain regarding the fate of photo-excitations and how their spectral signatures depend on crystal packing and morphology. The PI’s group has extended Kasha’s model, which is predicated entirely on long-range Coulombic coupling, to include short-range (super-exchange) coupling arising from intermolecular charge-transfer, as well as local coupling to the vinyl-stretching mode responsible for pronounced vibronic progressions in the UV-Vis spectra of a great many conjugated molecules. Although the model can predict with quantitative accuracy details of the absorption spectral line shape and correlate spectral features to the nature of the underlying excitons, it is limited in its ability to describe photoluminescence and energy transport, processes which often require the inclusion of excimers. Excimers, common in pi-conjugated molecules, arise when an electronic excited state relaxes along a “slow” intermolecular (phonon) coordinate resulting in featureless, red-shifted emission. In this project, the next generation of molecular H- and J-aggregate models will be developed which account for excimer formation and emission. The approach is based on a Holstein-Peierls Hamiltonian which includes electronic coupling along the slow-coordinate, is particularly strong in closely packed systems like π-stacks, where the intermolecular electron and hole transfer integrals are hypersensitive to small, sub-Angstrom, changes in the relative orientation of neighboring chromophores. The Holstein-Peierls approach enables all of the important physical processes to be treated on equal footing and fully quantum-mechanically. The model will be employed to account for the absorption and photoluminescence spectral line shapes in excimer-forming perylene diimide dimer complexes and larger π-stacks. The ability of excimers to function as energy traps will be investigated through analysis of the density matrix equations of motion. Libai Huang at Purdue University will collaborate and provide experimental validation by conducting spectroscopic measurements and femtosecond-resolved transport measurements of several perylene diimide derivatives which display varying degrees of excimer emission. The PI’s approach may enhance the likelihood for discovering new and potentially useful physical phenomena, as well as design strategies for controlling excimer formation for device applications.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.

非技术摘要该奖项支持理论/计算研究和教育有关光与有机分子制成的半导体材料相互作用的教育。更熟悉的半导体（如硅）是无机用于微电子和计算机芯片的硅。但是，基于有机分子的半导体具有较低的材料加工和更有利的机械性能等优点。有机材料继续侵入商业设备，例如显示器中使用的有机发光二极管或OLED（“ OLED”电视），太阳能电池，它们将阳光转化为电能，甚至是“可穿戴”的电子设备和传感器。 PI和他的研究团队将研究有机晶体和聚集体的光吸收和光发射等基本过程，以及分子之间如何传输光吸收的能量 - 与光合作用过程中植物中发生的能量相似。研究小组将通过基于量子力学的方程来进行理论投资，以描述有机分子如何对光的反应。方程将使用复杂的计算机算法解决。特别感兴趣的是某些称为准分子的电子激发态，它们会发出更长的波长，并将电子能量转换为光能的效率较低。 PI和他的团队将研究这种兴趣者如何形成，并最终如何设计避免质数形成的分子聚集体。拟议的活动还将通过与普渡大学的Libai Huang教授等实验者合作来增强研究基础设施，后者将采用国家或艺术实验技术来探测有机膜中的能源运输。总体而言，这项研究工作应该为基于有机材料的下一代电子设备的蓝图做出贡献。技术摘要该奖项支持理论和计算研究以及有关如何从有机分子制成的半导体材料中吸收或发射光的理论和计算研究。 PI共轭分子和聚合物的固体相继续受到宽度的关注，因为在现场效应晶体管，发光二极管和太阳能电池中的半导体材料。然而，尽管在Kasha开创了有关分子H和J聚集的开创性工作之后进行了五十多年的深入实验和理论研究，但有关光兴趣的命运以及它们的光谱特征如何取决于晶体包装和形态学，仍然存在重要的问题。 The PI’s group has extended Kasha’s model, which is predicted entirely on long-range Coulombic coupling, to include short-range (super-exchange) coupling arising from intermolecular charge-transfer, as well as local coupling to the vinyl-stretching mode responsible for pronounced vibronic progressions in the UV-Vis spectra of a great many conjugated molecules.尽管该模型可以通过定量准确性的细节进行抽象光谱线形状和相应的光谱特征进行预测，但它具有基础激子的性质，但其描述光量和能量传输的能力限制，即通常需要包含进券的过程。当电子激发态沿“缓慢”的分子间（声子）坐标放松而导致无特征，红移发射的“慢速”坐标时，将产生在PI共轭分子中常见的准分子。在该项目中，将开发下一代分子H和J聚集模型，以解释准分子的形成和排放。该方法是基于荷斯坦 - 佩尔斯·哈密顿（Holstein-Peierls Hamiltonian），其中包括沿慢速坐标的电子耦合，在π堆积的近距离系统中尤其强，其中分子间电子和孔传递积分对小型，子角的高度敏感，对邻近发色光的相对定向的变化。 Holstein-Peierls方法使所有重要的物理过程都可以在相等的基础上和机械量子上进行处理。该模型将用于解释精确二二烯二酰亚胺二聚二聚体配合物和较大的π堆的吸收和光致发光光谱线形状。准分子充当能量陷阱的能力将通过分析密度矩阵方程进行研究。普渡大学的Libai Huang将通过进行光谱测量值和飞秒分辨的运输测量来合作并提供实验验证，该测量表现出不同程度的进二二酰亚胺衍生物。 PI的方法可能会增强发现新的和潜在有用的物理现象的可能性，以及用于控制设备应用程序的Excimer形成的设计策略。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛的审查标准通过评估来通过评估来获得的支持。