Aromatic sulfonium polyoxometalates as photochromic materials and self-separating (PhD)

Abstract

The design and development of molecular materials that exhibit two or more properties of interest are gaining attention in recent years. These materials are often built on platforms like metal nanoparticles, metal organic frameworks, polymeric materials, and nanocomposites. Polyoxometalates (POMs), discrete, anionic metal oxide clusters of early transition metal ions, represent a vast class of inorganic materials possessing enormous diversity in their size, structure and properties which make them suitable in the field ranging from optical, magnetic, catalytic, biological and electronic applications. It is well-known that the properties of a hybrid POM can be engineered by systematically varying its organic counterions. These organic counterions can be fine-tuned through various substitutions like change of functional group, by introducing electron releasing and electron withdrawing group on the substituents, increasing the resonance in organic molecule or increasing and decreasing of chain length. The present thesis is focused on the two diverse materials properties of the POM organic hybrids. These properties are photochromism and self-separating catalysis. POMs owing to their ability to accept and release electrons make them attractive compounds for the development of photochromic materials. In POM-based photochromic materials, the photo-excitation leads to electron transfer from the cluster oxygen to metal ion generating reduced metal centers. The reduced metal centers in turn lead to the coloration of the material through various electronic transitions. In this regard, the organic counter cations of the anionic POM cluster play significant roles in deciding the photochromic properties of a POM hybrid. Organoammonium cations (OACs) are the common class of cations used in POM chemistry and a vast majority of the known photo-chromic POM materials are those containing OACs. Meanwhile, self-separating catalysts, which combine the properties of homogeneous and heterogeneous catalysts in a single entity, are becoming important in many industrial applications. It has advantages of both heterogeneous catalysts which include easy separation and recyclability, and homogenous catalysts which offer relatively high activity and improved