Excellence in Research: Structure and Dynamics of Exciplexes in Thermally Activated Delayed Fluorescence

在这个项目中，由综合活动办公室（OIA），化学系的化学结构，动力学和机制-A（CSDM-A）计划以及材料研究系的电子和光子材料（EMPs）计划共同资助，克拉克亚特兰大大学的塞汉萨尔曼和她的研究小组正在使用理论模型和计算工具来研究电子结构和光学性质。显示热激活延迟荧光（TADF）的有机发光二极管（OLED）材料的特性。该项目旨在根据其电子结构和光学性质，以及与激发态复合物相关的各种过渡过程，大大推进对激发态复合物（激基复合物）的理解。更好地了解这些物种的基本结构和动力学将有助于指导开发用于光学和电子设备的高效新材料，包括OLED，太阳能电池，场效应晶体管，（生物）化学传感器和存储设备。该项目还为来自科学领域代表性不足的群体的学生提供具有挑战性的研究经验和计算材料化学方面的专业培训，这将有助于他们为STEM（科学，技术，工程和数学）劳动力做好准备。该项目的主要目标是阐明基于激基复合物的OLED材料中热激活延迟荧光（TADF）的激发态动力学。这种系统代表了使用有机分子实现高效OLED的最有前途的材料类别之一，并且可以导致与该技术相关的制造成本的显著降低。激基复合物的电子结构和性质受激基复合物态分子间相互作用的影响，激基复合物态分子间相互作用明显不同于基态分子间相互作用，且相对较弱，导致激基复合物具有多种结构构象。激基复合物的电子结构、性质、电荷和能量转移过程的动力学等方面的研究对于其在有机发光器件中的应用具有重要意义。该项目使用最先进的计算方法，目标是量化微观参数并建立这些材料的结构-性能关系。该研究小组使用全原子分子动力学（AA-MD）模拟与密度泛函理论（DFT）计算相结合的综合方法来研究固体基质环境对激基复合物发射特性的影响。他们还在研究高能无序（静态和动态成分）对辐射衰变过程效率的影响。主-客体相互作用的影响以及电荷和能量转移过程的动力学也包括在建模方案中，以考虑系统间交叉和其他辐射和非辐射跃迁。该奖项反映了NSF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。

In this project, jointly funded by the Office of Integrative Activities (OIA), the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, and the Electronic and Photonic Materials (EPM) program in the Division of Materials Research, Seyhan Salman and her research group at Clark Atlanta University are using theoretical models and computational tools to investigate the electronic structure and optical properties of organic light-emitting diode (OLED) materials that exhibit thermally activated delayed fluorescence (TADF). The project seeks to significantly advance the understanding of excited-state complexes (exciplexes) that are responsible for TADF based on their electronic structures and optical properties, as well as the various transition processes associated with the excited complexes. Better understanding of the fundamental structure and dynamics of such species will help guide the development of efficient new materials for applications in optical and electronic devices, including OLEDs, solar cells, field-effect transistors, (bio)chemical sensors and storage devices. The project also provides students from groups that are underrepresented in science with a challenging research experience and professional training in computational materials chemistry that will help prepare them for the STEM (science, technology, engineering and mathematics) workforce.The main goal of this project is to elucidate the excited-state dynamics of thermally activated delayed fluorescence (TADF) in exciplex-based OLED materials. Such systems represent one of the most promising classes of materials for realizing highly efficient OLEDs using organic molecules and could lead to a significant reduction in fabrication costs associated with this technology. The electronic structure and properties of exciplexes are influenced by the intermolecular interactions in the exciplex state, which are markedly different than that in the ground state and are relatively weak, leading to various structural conformations. Further studies of exciplexes, including their electronic structures, properties, and dynamics of charge and energy transfer processes, are needed for their application in OLEDs. This project uses state-of-the-art computational approaches with the goal of quantifying microscopic parameters and establishing structure-property relationships in these materials. The research team uses an integrated approach combining all-atom molecular dynamics (AA-MD) simulations with density functional theory (DFT) calculations to study the effect of the solid matrix environment on the emissive properties of exciplexes. They are also examining the impact of energetic disorder (static and dynamic components) on the efficiency of radiative decay processes. The impacts of host-guest interactions and the dynamics of charge- and energy-transfer processes are also included in the modeling scheme in order to account for intersystem crossing and other radiative and non-radiative transitions.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.