Photoresponsive Stable Organic Radicals

Jana, Palash (2024) Photoresponsive Stable Organic Radicals. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Palash Jana (19RS072)) 19RS072.pdf - Submitted Version Restricted to Repository staff only Download (16MB)

Abstract

The thesis primarily aims to address the light-mediated control over the molecular spin state of the dimethyldihydropyrene-based stable organic radicals. The later part of the thesis also contributes to a new problem associated with machine learning in chemistry and its application in the development of a cross-reactive sensor array designed to detect and discriminate among biologically important analytes using the principles of multivariate analysis. The research involved the synthesis, characterization, and detailed photophysical studies of the synthesized systems. The introductory chapter, Chapter 1, covers the principles and recent examples of all-organic radical/radicaloid systems that undergo light-driven spin state switching. It also addresses the challenges associated with the design principles and practical implementation of these systems and explores prospects for improved understanding and manipulation. Chapter 2 deals with a diradicaloid system on Boekelheide’s dimethyldihydropyrene (DHP) scaffold where the aromaticity of the 14π DHP system was perturbed through the construction of the corresponding quinoidal form. The aromaticity was subsequently restored as the system underwent a transition to a biradical structure centered on two exocyclic carbons. Upon photoexcitation, the system could be converted to a radical anion and di-anionic form easily when dimethylformamide was used as a solvent. Chapter 3 demonstrates the synthesis of aryldicyanomethyl-based stable organic radicals on the photoswitchable dimethyldihydropyrene (DHP) scaffold. The photoisomerization of the DHP moiety leads to reversible generation and extinction of radicals via the dissociation and formation of the sigma bond, respectively. The magnetism of the systems investigated by electron paramagnetic resonance (EPR) displayed that switching from a non-magnetic closed-shell to a magnetic open-shell structure could be achieved by the photoisomerization of the DHP photoswitch. Chapter 4 focuses on the selective detection of adrenaline hormone via the formation of a donor-acceptor Stenhouse adduct (DASA) in the presence of an activated furfural. Furthermore, error-free detection and quantitative prediction of epinephrine concentration with high precision were achieved using machine learning techniques. Chapter 5 deals with a two-component aggregation-induced emissive (AIE) probe capable of interacting with sialic acid (SA) and other saccharides via noncovalent interactions, producing unique emission fingerprints. Analysis of the output signals enabled the reliable detection and clear discrimination of SA in the presence of other saccharides with high accuracy. Additionally, the potential application of this probe in cellular glycan mapping was explored through fluorescence imaging and surface-enhanced Raman scattering with human breast cancer cells.

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