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Abstract:
The aim of the work presented in this thesis is to develop more efficient methods for the synthesis of oligomers and polymers that can adopt stable secondary conformations in solution, to gain a more profound understanding of their folding behavior, and to utilize the reversible helix-coil transition for tubular scaffolding and the design of stimuli-responsive materials.
Chapter 2
The folding of oligo(phenylene ethynylene)s has already been discussed in the general introduction. We aimed to extend this concept to the polymer level. The problems associated with the synthesis of high molecular weight meta-PPEs and relatively few examples in literature motivated us to develop a new synthetic method. Chapter 2 describes this method to access high molecular weight m-PPEs.
Chapter 3
The reversible helix-coil transition in foldamers allows to populate the global minimum structure and therefore provides a means to repair local defects. However, from a materials standpoint this reversibility might also constitute a disadvantage with regard to structural integrity and hence device stability/lifetime under a variety of environmental conditions. Chapter 3 describes the synthesis and post-functionalization of a m-PPE foldamer to furnish covalently stabilized helical structures.
Chapter 4
Identification of new folding backbones and their synthesis present a challenging task. Chapter 4 describes the synthesis of ortho- linked PPEs. The synthesis takes advantage of our method (chapter 2) to synthesize defect free PPEs.
Chapter 5
The helix-coil equilibrium in synthetic foldamers have been governed so far by quality of solvent, temperature, hydrogen bonding and metal complexation. We have demonstrated the possibility of using light as an external stimulus to control the secondary conformation of azobenzene-containing foldamers. Chapter 5 describes the synthesis and photoresponsive properties of these oligomers.
Chapter 6
The electroluminescent and photoluminescent properties of conjugated polymers have made them attractive candidates for organic electronics. However, the presence of defects in a polymer incorporated during synthesis can be harmful to the lifetime and performance of a device. With a good method in hand, Chapter 6 describes our synthesis of site-isolated, defect-free, and water soluble para-linked PPE, which shows remarkable fluorescence efficiency in water.
