Probing redox and photoredox activity in metal-organic frameworks.

NON-TECHNICAL SUMMARY: This project, supported through the Solid State Materials and Chemistry Program in the Division of Materials Research, focuses on studying metal-organic frameworks, a class of porous materials with diverse potential applications ranging from fuel cell technology to industrial chemical production to solar energy conversion. Despite significant advancements in designing and developing novel frameworks for these purposes, there remains a significant gap in understanding how these materials function. This research employs several X-ray and optical characterization tools to gain fundamental insights into the properties and processes behind the applications, including how charges move and are distributed throughout these frameworks. The outcome of this work is essential for facilitating the rational design of the next generation of these materials with improved performances, thereby impacting a broad range of energy and environmental sustainability efforts. Furthermore, as part of a broader mission to integrate research in education, the outreach component of the project provides hands-on research experiences for high school science teachers in the Newark region and a mechanism for translating those experiences into meaningful high school science curricula that meet the specific needs of the students in this urban community. This outreach initiative has a large impact on the students in these schools by directly engaging their educators. TECHNICAL SUMMARY: The research in this project, supported through the Solid State Materials and Chemistry Program in the Division of Materials Research, targets an understanding of fundamental structure/function relationships in redox and photoredox active metal organic frameworks (MOFs), a class of hybrid materials composed of metal ions or clusters connected by organic molecules to form crystalline microporous networks. Their inherent porous nature and tunable architecture and composition of these frameworks allow electronic structure (i.e.bandgap) manipulation, selective guest species interaction and the incorporation of redox active components and other synergistic characteristics. These multifaceted framework functionalities invariably give rise to complex structure-function relationships, involving electronic rearrangement, charge delocalization and cooperative interactions of the framework host and guest species. Redox active MOFs therefore not only engender emerging technological interest but serve as a unique and fascinating platform for fundamental studies of host-guest chemistry, electron transfer and organometallic photophysics in 3D coordination space. The project focuses on MOF systems that exhibit electron reduction and oxidation (redox) behavior in the ground state, excited state and/or associated with donor-acceptor host-guest interaction. The principal objective in studying these systems is to investigate the nature of electron transfer in these systems, including the role of electronic delocalization and/or cooperativity among and between metal sites, organic linkers and molecular guest species. To accomplish this goal, a targeted set of optical, vibrational and X-ray spectroscopy methods are employed in combinations of steady state, in situ, and in some cases time-resolved studies of MOF systems to garner real time information on their electronics, photophysics, host-guest interactions and molecular level structure changes with respect to the overall framework structure. Correlating these insights with their observed performance (or some proxy of their performance) in terms of conductivity, catalytic, electrocatalytic or photocatalytic behavior reveals the mechanisms behind their redox behavior and establish design principles for improved functionality in applications such as (photo)electrocatalysis. 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.