Stimuli-responsive organic materials based on stable free radicals spin switching
The following dissertation explores and describes the research from two main directions: 1) development of stimuli-responsive organic materials based on stable free radicals, and 2) synthesis, reaction scope, and the proposed mechanism of oxidative esterification reaction of cyclohexane hexacarboxylic acid.
Changes in the quantum mechanical property of the electron spin and the responsive changes in physical properties of a material are very intriguing and promising possibilities to investigate. The first part of this dissertation explores stable free radicals spin switching. In particular, Chapter 2 explores strength and nature of the viologen cation radical pi bond. Pi bonds are often exploited in the design of supramolecular assemblies in water. Here, the first systematic investigation of the effect of the viologen cation radical structure on pimer bond has been provided. A library of viologen cation radicals has been synthesized and studied. The findings suggest that the pi bond strength is essentially insensitive to increased conjugation, as well as to substitution with electron-withdrawing or electron-donating groups. Furthermore, the interaction is undiminished by sterically bulky N-alkyl groups, and shows no observable preference for social self-sorting between electron-rich and electron-poor radical cations. Chapter 3 explores switch-on paramagnetic probes based on a covalently linked viologen radical cation dyad. Changes in optical and magnetic properties are observed upon temperature cycling. This reversible thermomagnetic switch in water and cycling between diamagnetic and paramagnetic forms were followed using EPR and UV-Vis spectroscopy.
The second part of this dissertation describes access to previously unknown aryl mellitic acid esters which may be useful in domino self-immolative linkers or as the cores of paddlewheel dendrimers. Chapter 4 explores the scope of the reaction and mechanistic considerations of the one-pot solvent-free oxidative esterification.