Collaborative Research: Excited-State Dynamics in Organic Charge-Transfer Compounds: An Experimental and Theoretical Study

非技术性说明：该项目是一项研究由碳基有机分子组成的晶体，其导电方式类似于构成计算机芯片的硅的行为。 该项目旨在更全面地了解这些有机材料如何对光做出反应，以及通过它们的电流如何受到分子振动的影响。 测量晶体吸收和发射的光的实验与晶体中电子的各种能量的计算进行了比较。从这些实验和计算中，现在可以确定分子的振动如何影响负责电流的电子，从而获得对这些材料的电子特性的基本理解。 该项目的研究结果有助于确定用于制造更高效，更便宜的电子设备的最佳材料，如平板电视和其他媒体，光电传感器和太阳能电池的显示器。 参与该项目的研究生和本科生正在培养实验和计算方面的宝贵技能，同时为满足国家和全球社会对更高效和可持续技术的需求做出贡献。技术描述：有机半导体由于其在太阳能电池和光电传感器等光电应用方面的潜力而受到极大关注。 由两种或更多种不同的有机分子组成的电荷转移化合物，其中一种物质作为电荷供体，另一种物质作为受体，可以提供新的性质或改进的性能，以增加有机半导体的应用范围。该项目的目标是阐明选定的电荷转移化合物的激发态动力学，并深入了解其中的电子耦合和电子-声子耦合。 电荷输运和激发态动力学过程对于这些材料在光电器件中的应用至关重要，并且取决于电子和电子-声子相互作用之间的微妙相互作用。 瞬态吸收和荧光寿命的测量，当解释在光的各种电子转移过程的速率的计算评估，允许在这些材料中的激子的衰变模式被确定。共振拉曼实验被用来提取弛豫能和转移积分。 这些实验结果解释光的网站能量，电子-声子和电子耦合计算使用各种方法，包括密度泛函理论计算的大分子团簇和那些基于周期性边界条件，半经验的方法，紧束缚模型，和分子动力学模拟。 这一系列强耦合的实验研究和理论建模打开了一个大范围的功能不表现在单分子固体。这些发现最终有助于满足国家和全球社会对更高效和可持续技术的需求。

Non-technical description: This project is a study of crystals made up of carbon-based organic molecules that conduct electricity in a way similar to the behavior of the silicon that makes up computer chips. The project aims to develop a fuller understanding of how these organic materials respond to light, and how the flow of electricity through them is affected by the vibrations of the molecules. Experiments that measure light absorbed and emitted by the crystals are compared to calculations of the various energies of the electrons in the crystal. From these experiments and calculations it is now possible to determine how the vibrations of the molecules affect the electrons that are responsible for the flow of electricity, thus gaining fundamental understanding of the electronic properties of these materials. The findings of this project help determine the best materials to use to make more efficient and cheaper electronic devices such as displays for flat-screen TVs and other media, photosensors, and solar cells. Graduate students and undergraduates participating in the project are developing valuable skills in experimentation and computation while contributing to fulfilling a national and global societal need for more efficient and sustainable technology.Technical description: Organic semiconductors are of significant interest due to their potential for opto-electronic applications such as solar cells and photosensors. Charge transfer compounds, which are made of two or more different organic molecules in which one species acts as a donor of electric charge and the other as an acceptor, could provide new properties or improved performance to increase the range of application of organic semiconductors. The goals of this project are to elucidate the excited-state dynamics of selected charge transfer compounds and develop a deep understanding of electronic couplings and electron-phonon couplings in them. Charge transport and excited-state dynamical processes are critical to applications of these materials in opto-electronic devices, and depend on a subtle interplay between electronic and electron-phonon interactions. Transient absorption and fluorescence lifetime measurements, when interpreted in light of computational evaluation of the rates of various electron-transfer processes, allow the decay mode of excitons in these materials to be determined. Resonant Raman experiments are used to extract relaxation energies and transfer integrals. These experimental findings are interpreted in light of site energies, electron-phonon and electronic couplings computed using a variety of methods, including density functional theory calculations of large molecular clusters and those based on periodic boundary conditions, semi-empirical approaches, and tight-binding models, and molecular dynamics simulations. This strongly-coupled series of experimental investigations and theoretical modeling opens a large range of functionalities not manifest in monomolecular solids. The findings ultimately contribute to fulfilling a national and global societal need for more efficient and sustainable technology.