Date of Award
Doctor of Philosophy (PhD)
Dr. Sourav Saha
Dr. Julia L. Brumaghim
Dr. Stephen E. Creager
Dr. William T. Pennington
Metal-organic frameworks (MOFs), a class of porous materials made of organic ligands linked by metal ions or cluster nodes, are well known for their highly ordered crystalline structure and chemical and structural tunability. Due to their porous nature, MOFs can encapsulate guest molecules inside the cavities. The tunable structures, compositions, porosity, and surface area make MOFs useful for various applications, such as gas storage and separation, chemical sensing, catalysis, optoelectronics, and drug delivery.
In chapter 2, I present a new luminescent metal-organic framework (LMOF) featuring energy transfer and stimuli (Hg2+) responsive capabilities. The two fluorophoric ligands incorporated in the LMOF framework have complementary absorption and emission, which allows ligand-to-ligand energy transfer. Therefore, upon excitation, the donor transfers the excitation energy to the acceptor chromophore via Fӧrster resonance energy transfer (FRET), and as a result, the MOF emission stemmed from the lower energy emitter (acceptor chromophore). In addition to this, our MOF displayed significant red-shift and quenching of its photoluminescence in the presence of Hg2+ solution while only a modest fluorescence quenching but no spectral shifts in the presence of other transition metal ions. Moreover, the framework structure remained intact after exposure to Hg2+ and other transition metal ions, and its original photoluminescence spectrum could be restored by simple washing, making it a promising reusable Hg2+ sensor. These studies demonstrate the light-harvesting and toxic Hg2+ sensing capabilities of a new luminescent MOF.
Chapter 3 focuses on the tuning of the optical and electrical bandgap of a MOF-74 analog. The MOF-74 was constructed from an electron-deficient naphthalene diimide-based ligand containing two salicylic acid groups to coordinate with Zn2+ metal ion. To tune the bandgap of this MOF-74, an electron-rich guest (tetrathiafulvalene; TTF) guests are encapsulated along the wall of the framework. This arrangement of the TTF in the framework increases the electron delocalization via π-π stacking, resulting in the reduction of the bandgap of the MOF by approximately 1 eV.
Studies presented in chapter 4 investigate the improvement of the electrical conductivity of an insulating MOF by introducing conductive polymers inside the MOF cavities. In this study, the MOF was loaded with the monomers (EDOT and Py) of the respective conductive polymers (PEDOT and PPy), and polymerization was carried out in the presence of an oxidant (iodine). The resulting MOF-polymer composites exhibit a significantly higher conductivity in comparison to the pristine insulating MOF.
Khatun, Amina, "Stimuli-Responsive and Electrically Conductive Metal-Organic Frameworks" (2021). All Dissertations. 2961.