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

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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.