Porphyrin Based Metal Organic Frameworks for Photocatalysis and Gas Adsorption Supported by EPR Study

Abstract

Porphyrin based metal organic frameworks (PMOFs), a subset of metal organic frameworks (MOFs), are crystalline porous materials with unique features. Since their initial introduction, PMOFs have garnered increasing research attention due to the distinctive electronic, chemical, and physical attributes of metalloporphyrins. Over recent years, there has been a growing number of intricately designed PMOFs that exhibit captivating chemical and physical characteristics. This makes them promising candidates for various applications, such as artificial light-harvesting systems, photocatalysis reactions, gas storage/separation, sensing, photodynamic therapy, and more. This thesis focuses on studying photocatalytic organic transformations and binding of small molecules (O2, CO, NO) in porphyrin MOFs by employing EPR. During this PhD research, the fundamental features of porphyrin frameworks, as well as their practical applications, have been investigated. For example, the synthesis and properties of porphyrin metal organic frameworks using elongated porphyrin linkers coordinated to stable secondary building units like zirconium or hafnium have been studied. Zr-PMOFs, for example, showed high porosity and stability, allowing for using them in heterogenous photocatalysis reaction for benzene hydroxylation. In addition, Hf-PMOF exhibited high stability due to its interpenetrating structure, which allows the recycling of the frameworks after being used for photoreduction of nitroaromatics. Their features were improved by doping metal ions into the porphyrin core, resulting in high photocatalytic activity and ability for gas adsorption. Electron paramagnetic resonance spectroscopy (EPR) study was involved to probe the reaction mechanism during the transformation of organic substrates. Further, the coordination of small gaseous molecules, such as O2, CO, and NO, with the Co metal ion in the centre of the porphyrin MOF probed via EPR as the changes in the electronic structure of both the metal centre and the gaseous species could be detected.