Singlet Fission, Triplet Upconversion, and Thermally-Activated Delayed Fluorescence: Controlling Exciton Dynamics with Metal-Organic Frameworks

理解和控制光与物质的相互作用对于许多技术都是至关重要的，这些技术包括吸收光产生电的太阳能光伏电池和利用电产生光的发光二极管。控制这些现代设备效率的过程取决于许多变量。其中一些变量，比如组成设备的分子结构，我们可以通过分子设计来控制。然而，一些变量仍然难以控制，因为它们取决于分子在空间上的排列方式，而不是每个分子的单个结构。这种超分子排列通常不能由传统的化学合成决定。这个项目得到了材料研究部固态与材料化学项目和电子与光子材料项目的支持，Dinca教授和他的研究小组解决了这个挑战：最终控制分子之间的排列方式，这样当光与这些分子形成的固体相互作用时，形成的能量，称为激子，可以被量化和指导。这提供了对能量如何在固体中传输的更深入的理解，最终为提高现代设备（如有机光伏、发光二极管和其他光学设备）的效率提供了蓝图。作为该奖项的一部分，首席研究员还为研究生和本科生提供与材料合成有关的广泛问题的培训，以及光物理研究和相关分析技术，并参与波士顿地区的推广活动。激子是光与物质相互作用时形成的束缚电子-空穴对。尽管人们对激子的形成和它们在固体中的传播方式了解很多，但对如何控制它们却知之甚少。因此，尽管激子动力学对于确定太阳能电池、发光二极管和有机激光器等一系列技术的效率具有重要意义，但在控制产生激子的有机成分的相对方向方面，还没有明确的合成处理方法。事实上，固态发色团分子之间的距离和角度与激子扩散和寿命密切相关，但目前的技术和材料不允许系统地控制这些指标。该项目由材料研究部固态与材料化学项目和电子与光子材料项目支持，研究一类固体，其中有机分子之间的距离和角度可以系统地调整，即使在亚埃状态下也称为金属-有机框架。Dinca教授和他的研究小组使用金属有机框架来证明控制激子形成和动力学的能力。本项目特别关注涉及激子的三个重要过程：单线态裂变、三重态上转换和热激活延迟荧光。这三个过程主要取决于相邻有机分子的相对取向，以及参与光吸收的特定发色团的分子构象或形状。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。

Non-technical summaryUnderstanding and controlling the interaction of light with matter is of fundamental importance for a number of technologies including solar photovoltaic cells, which absorb light to produce electricity, and light-emitting diodes, which use electricity to produce light. The processes that control the efficiency of these modern-day devices depend on many variables. Some of these variables, such as the structure of the molecules that make up the devices, we can control by molecular design. However, some variables are still difficult to control because they depend on how molecules are arranged spatially with respect to each other, rather than the individual structure of each molecule. This supra-molecular arrangement cannot typically be dictated by traditional chemical synthesis. With this project, supported by the Solid State and Materials Chemistry Program and the Electronic and Photonic Materials Program in the Division of Materials Research, Prof. Dinca and his research group tackle this challenge: to ultimately control how molecules are arranged with respect to each other such that when light interacts with the solids made by these molecules, the energy formed, called an exciton, can be quantified and directed. This provides a deeper understanding of how energy is transported within solids, to ultimately provide a blueprint to increase the efficiency of modern devices such as organic photovoltaics, light-emitting diodes, and other optical devices. As part of this award the principal investigator also provides training for graduate and undergraduate students in issues related broadly to synthesis of materials, as well as photophysical investigations and related analytical techniques, and engages in outreach activities in the Boston area.Technical summaryExcitons are bound electron-hole pairs that form when light interacts with matter. Although much is understood about how excitons form and how they travel within solids, little is known about how to control them. As such, despite the importance of exciton dynamics for determining efficiencies in a range of technologies from solar cells to light-emitting diodes and organic lasers, there are no clear synthetic handles on controlling the relative orientation of the organic components that give rise to excitons. Indeed, the distance and angles between chromophore molecules in the solid state, is intimately involved in determining exciton diffusion and lifetimes, but current techniques and materials do not allow systematic control of these metrics. This project, supported by the Solid State and Materials Chemistry Program and the Electronic and Photonic Materials Program in the Division of Materials Research investigates a class of solids where the distance and the angles between organic molecules can be systematically tuned even in the sub-angstrom regime called metal-organic frameworks. Prof. Dinca and his research group use metal-organic frameworks to demonstrate the ability to control exciton formation and dynamics. In particular, this project focuses on three important processes involving excitons: singlet fission, triplet upconversion, and thermally-activated delayed fluorescence. All three processes depend critically on the relative orientation of neighboring organic molecules, as well as on the molecular conformation or shape of the particular chromophore involved in light absorption.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.