Blooming of Diverse Photocatalytic Reaction Strategies by a Heterogeneous Platform of Covalent Organic Framework

Ayan, Jati (2024) Blooming of Diverse Photocatalytic Reaction Strategies by a Heterogeneous Platform of Covalent Organic Framework. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Ayan Jati (19RS035)) 19RS035.pdf - Submitted Version Restricted to Repository staff only Download (70MB)

Abstract

Catalysis plays an indispensable role in the advancement of new pharmaceuticals, agrochemicals, cutting-edge materials, and fine chemicals. Decades of meticulous research have enabled the precise description and customization of active sites in both homogeneous and enzyme catalysis, unlocking a new level of control and efficiency. Today’s focus on designing robust and selective catalysts has become pivotal in addressing critical global challenges such as sustainability, economic constraints, and waste reduction. Catalyst engineers are now tasked with the delicate art of designing the "active site" to interact optimally with specific molecular groups throughout the reaction cycle, thereby enhancing efficiency, minimizing waste, and ensuring high product selectivity. In recent years, remarkable strides have been made in mild and greener strategies by a photocatalytic platform. A variety of photocatalytic reactions, including cross-coupling and small molecule synthesis, have advanced significantly through innovative approaches in photoredox and transition-metal dual catalysis. In advanced homogeneous catalysis, photosensitizers and redox catalysts are often employed separately, frequently requiring external ligands to drive the reaction. However, the heavy reliance on costly, non-recyclable noble-metal-based photocatalysts undermines the sustainability of these processes. Moreover, the lack of synergy between the distinct catalysts introduces additional complexities in reaction design. Multinuclear catalyst deactivation, such as the formation of nickel black, exacerbates these challenges, leading to high catalyst loading requirements and compromised reproducibility. Semi-heterogeneous strategies, which combine the benefits of both homogeneous and heterogeneous catalysis, have recently gained traction. Reusable organo-semiconducting materials are increasingly being explored as photosensitizers, yet the redox catalyst remains non-recyclable, limiting the overall sustainability of these systems. In this evolving landscape, covalent organic frameworks (COFs) have emerged as exceptional contenders in heterogeneous catalysis. These porous, crystalline materials can be meticulously engineered to provide structural stability while incorporating highly active catalytic sites, with fine-tuned control over their function. The π-extended structures of COFs grant them natural light-harvesting and energy-transfer capabilities, which can be enhanced through pre- or post-synthetic modifications. While current research in COF-based photocatalysis is primarily concentrated on solar energy harvesting for processes like proton and carbon dioxide reduction, COFs also hold immense promise as platforms for anchoring redox-active precatalysts. Their ability to function as sustainable sensitizers in light-driven fine chemical synthesis could revolutionize the field. My research aims to introduce COFs as a new class of photocatalysts for the efficient and sustainable synthesis of fine chemicals. To this end, I have employed several innovative strategies, which are explored in detail in the following chapters of my thesis. Though this work, I hope to contribute to the growing body of knowledge in photocatalysis, paving the way for more sustainable and economically viable catalytic processes.

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