This project focused on understanding fundamental structure/function relationships in an emerging class of hybrid materials called metal organic frameworks (MOFs). Composed of metal ions or clusters connected by organic molecules to form crystalline microporous networks, MOFs possess unique adsorption and electronic properties that not only engender emerging technological interest but serve as a fascinating platform for fundamental studies of host-guest chemistry and organometallic photophysics. The research primarily focused on MOF systems that allowed the exploration of several exploitable MOF properties ranging from gas adsorption to heterogeneous catalysis to light harvesting and photocatalysis. The objectives in studying these systems were to expose pertinent electronic and molecular level structural changes associated with the observed properties and use these insights to help better understand their functionalities. To accomplish these goals, the research portion of this project examined several of these unknown and underexplored fundamental aspects using a targeted set of vibrational, optical, and X-ray spectroscopy methods. These electronically and structurally sensitive spectroscopy methods were employed, often times through in situ or time-resolved means, in the studies of MOF systems to garner real time information on the important host-guest interactions and structural changes.

Intellectual Merit outcomes:

This multipronged spectroscopic approach enabled us to pinpoint or confirm specific gas or other guest molecule adsorption sites within the material and determine the associated molecular level structural changes of the frameworks for gas separation applications for example.  Other spectroscopic interrogations, using a combination of vibrational, X-ray absorption and X-ray emission spectroscopy revealed the role of MOF pore size restrictions on specific host guest interactions, which, in turn can effectively be used to control framework metal oxidation and/or spin state. These fundamental investigations provided new insight on MOF design for the type of controlled reactivity needed in next generation catalysts. The project also included spectroscopic studies of photo-active MOFs, namely those potentially undergoing light-induced charge transfer events. The presence of long-lived photo-induced charge-separated excited states in MOFs, as in other materials, can enhance their photocatalytic activity by increasing the probability of transferring the charge to adsorbed reactants rather than recombine to its original unaltered electronic state. Some MOF materials had been studied as photocatalyst but the charge separated nature of the excited state had not been definitively assigned.  In this project, we used element specific time-resolved X-ray spectroscopy methods to unambiguously determine the involvement of the framework metal node sites in the light-induced charge separation processes and confirm the long lifetime compared to molecular analogues. The results of this project on host-guest interactions and photoactivity of MOF materials not only provided new molecular level insights that have relevance to their reported catalytic/photocatalytic behavior, but also established the feasibility, advantages, and in some cases limitations, of the different spectroscopy methods used for advanced molecular level characterization of these materials. In other words, this project laid the important foundation for applying these methods to MOF and related hybrid materials in future work.

Broader impact outcomes:

Enhanced understanding of MOF behavior afforded by this research project has far reaching implications for a broad range of MOF applications ranging from industrial chemical production to solar energy conversion. Furthermore, as part of a broader mission to integrate research in education, the professional development program from the outreach component of this project provided hands-on research experiences for a total of 6 different high school chemistry teachers from public school districts in the Newark, NJ region over the course of 5 summers. These teachers then translated those experiences into meaningful high school science curricula for their classrooms. This outreach initiative had a large impact on the students in these schools since it directly targeted their educators.

Last Modified: 08/05/2021
Modified by: Jenny V Lockard