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

非技术描述：这个项目是对由碳基有机分子组成的晶体的研究，这些分子的导电方式类似于组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是如何受到分子振动的影响的。测量晶体吸收和发射的光的实验与计算晶体中电子的各种能量进行了比较。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，从而对这些材料的电子性质有了基本的了解。该项目的发现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的显示器、光电传感器和太阳能电池。参与该项目的研究生和本科生正在培养宝贵的实验和计算技能，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：有机半导体因其在太阳能电池和光电传感器等光电子应用方面的潜力而引起人们的极大兴趣。电荷转移化合物由两个或两个以上不同的有机分子组成，其中一个物种作为电荷的供体，另一个物种作为受体，它可以提供新的性能或改善性能，以扩大有机半导体的应用范围。本项目的目标是阐明所选电荷转移化合物的激发态动力学，并加深对其中的电子耦合和电子-声子耦合的理解。电荷输运和激发态动力学过程是这些材料在光电子器件中应用的关键，依赖于电子和电子-声子相互作用之间的微妙相互作用。瞬时吸收和荧光寿命测量，当根据各种电子转移过程的速率的计算评估来解释时，允许确定这些材料中激子的衰减模式。共振拉曼实验用于提取弛豫能和传递积分。这些实验结果是根据用各种方法计算的格点能量、电子-声子和电子耦合来解释的，这些方法包括大分子团簇的密度泛函理论计算和基于周期边界条件的计算、半经验方法、紧束缚模型和分子动力学模拟。这种强耦合的一系列实验研究和理论模拟打开了单分子固体中没有表现出来的大范围的功能。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.