Date: Thursday, April 7, 2022
Time: 11:00 am - 12:30 pm EST

Plenary Lecture

Speaker: Dr. Linda Shimizu

Affiliation: Professor of Chemistry, University of South Carolina

Title of Talk: Exploring electron transfer and polymerization reactions within self-assembled bis-urea macrocycles.

Abstract: Porous organic crystals have applications as nanocontainers for reactions, in sensing, and for molecular separations. The Shimizu group utilizes the columnar assembly of bis-urea macrocycles to afford porous molecular crystals. Herein, we will examine the effect of organizing triphenylamines (TPAs) into the bis-urea macrocyclic building block to give functional materials, in which redox active TPA reside within the walls of the nanotubes. Upon activation, these crystals undergo guest exchange in single-crystal-to-single-crystal transformations, which generates a series of isoskeletal host-guest complexes that can be directly compared. This presentation will examine the loading of guests that have favorable reduction potentials and probe the electron transfer from host to guests. In addition, monomers that can undergo polymerization reactions to afford conjugated polymers within the narrow cylindrical nanochannels will also be explored. Overall, these studies give insight into the design of functional host-guest complexes for potential applications in sensing and molecular electronics.

Time: 11:00 am

Short Talks

Speaker: Dr. Thomas Schroeder

Affiliation: Postdoctoral Fellow, Harvard University

Title of Talk: Spatiotemporal control over crystal growth via hydrogel patterning

Abstract: Crystalline materials are ubiquitous, making crystal growth a fundamentally important process. Polymer additives are frequently used to control crystal growth, both in engineered contexts and in biology. Here, I will demonstrate that polymerization patterns within metastable hydrogels can exert profound influence on the exothermic growth of salt hydrates commonly used as “phase change materials” for thermal energy storage. Crystals grow faster in unpolymerized domains than in the polymerized bulk, on the order of millimeters per second, imparting control over both the timecourse of the material’s solidification and the resulting grain size distribution. This faster growth is accompanied by commensurately fast heat release, leading to “hotspots” in the unpolymerized domains where the temperature can exceed that of the bulk by 15˚C. This temperature difference can be harnessed to selectively activate downstream thermoresponsive processes in desired regions, enabling the engineering of complex, dynamic energy transduction cascades.

Time: 11:30 am

Speaker: Sylvia Hanna

Affiliation: Ph.D. Graduate Student, Northwestern University

Title of Talk: Discovery of spontaneous de-interpenetration through charged point-point repulsions

Abstract: Energetically driven reduction of porosity through entanglement is ubiquitous in nature and synthetic systems. This entanglement decreases valuable internal pore space useful for applications, such as catalysis, storage, and sensing. Here, I will describe our discovery of spontaneous de-interpenetration in a 6-fold interpenetrated uranium-based metal-organic framework (MOF), NU-1303-6. De-interpenetration transforms NU-1303-6 (14.2 and 19.8 Å pores) to its larger pore (40.7 Å) non-interpenetrated counterpart, which possesses a record-high void fraction and pore volume. Density functional theory calculations reveal that charged point-point repulsions between anionic, closely positioned uranium-based nodes drive this phenomenon. These repulsions compete with water molecules that hydrogen bond nearby networks together, favoring interpenetration. Controlling the interplay between these intermolecular forces enables the reversal of omnipresent energetic equilibria, leading to thermodynamically favored open pore structures. The discovery of charged point-point repulsion will likely lead to the re-evaluation of non-interpenetrated network design, synthesis, and wide-reaching applications.

Time: 12:05 pm EST