About the event
Speaker: Matthew J. Hurlock
Presentation Title: Study of the Structures and Properties of Tetraphenylethene-Based Coordination Polymers
Porous materials can be used to help some of the most pressing issues such as carbon capture, energy storage, and the detection of environmental hazards.1-3 Amongst porous materials Metal–Organic Frameworks (MOFs), a type of coordination polymer, stand out due to periodic structures and facile tunability. However, it is not always easy to predict how structural changes will affect the photophysical properties of the MOF. The luminescence of MOFs is complex and includes metal-based emissions, guest-based emissions, and ligand-based emissions. Tetraphenylethene-based ligands are ideal candidates for exploring the relationships between structure and photophysical properties in luminescent MOFs. This is due to ease of functionalization, high quantum yields, and luminescence in the solid-state. This talk will explore the synthesis and characterization of a series of tetraphenylethene-based luminescent MOFs. Using the tetra-carboxylate ligand, p-ETTC (Figure. 1, top left), a zirconium MOF was synthesized.4 This MOF has an interpenetrated structure and displays a yellow-green ligand-based emission. The tunability of the luminescence was studied through post-synthetic modification of the structure. This was accomplished by inserting two different dicarboxylate ligands. In both cases, the secondary ligands caused a dramatic shift in emission (Figure 1). This shift could be further tuned by functionalization of the inserted ligands. The ligand, m-ETTC (Figure 1, bottom left), was synthesized to explore ligand geometry effects on structure and luminescence. A zirconium structure was not achievable with this ligand, so other metals that would allow ligand-based luminescence were investigated. A cadmium–m-ETTC structure was synthesized and though it is luminescence, it is not porous owing to the dense structure.5 To enhance the porosity, a pillar ligand was added during synthesis. This caused coordination changes to the cadmium leading to a different structure that contains pores and red-shifted the emission (Figure 1).
Another method to affect the luminescence of MOFs is changing the origin of the emission, such as metal-based emissions. Lanthanides have well-studied luminescence that is characterized by distinct narrow emissions but low absorptions. To mitigate these adsorption issues, organic chromophores can be used as an antenna. MOFs make ideal scaffolds for this effect. Using the tetraphenylethene-based ligand, m-ETTC, a series of MOFs have been synthesized with the entire lanthanide series, not including promethium. A variety of structures have been synthesized and all but one of these structures are 2-dimensional. Interestingly, the luminescence of the ligand dominates and no lanthanide luminescence has been observed. Ongoing work is being done to elucidate the origins of this phenomenon. In this presentation key structural modifications and their effects on photoluminescence and other properties will be discussed.