Conjugated polymers and designed interfaces : conformational analysis and applications

Abstract

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.Cataloged from PDF version of thesis. Pages 160 and 161 are blank.Includes bibliographical references.The conformations of conjugated polymers can be altered by nearby environments. The intrapolymer conformation and interpolymer assemblies have a crucial impact on a variety of properties such as absorption, energy migration, and fluorescence. In this dissertation, the conformational changes and their effects on photophysics in different environments will be discussed. In Chapter 1, the basic principles to understand this thesis will be reviewed, including the processes of absorption and emission, exciton migration, the Langmuir-Blodgett technique, and interfacial phenomena. In Chapter 2, the conformational control and alignment of conjugated polymers at the air-water interface and how this alignment of polymers can lead to new emissive aggregates will be presented. The emission has the characteristics of excimers with the improved fluorescence quantum yields. The transfer of the aligned aggregates to glass substrates is attempted and these excimer films undergo reorganization upon exposure to solvent vapors, which triggers the fluorescence color change from yellow to cyan, leading to fluorescence-based chemical sensors. In Chapter 3, exciton migration to low-energy emissive traps at amphiphilic interfaces will be discussed. This chapter will deliver the design of interfaces and how the exciton migration can occur at the air-water interface and the hydrocarbon-water interface in lyotropic liquid crystals. To expand this interfacial exciton migration to more generalizable interfaces, Chapter 4 will show the fabrication of oil-in-water emulsions and how exciton migration in oil-in-water emulsion can produce distinct fluorescences between solution and interfaces. Chapter 5 will discuss the structural variations of novel functional conjugated polymers and how substituents can change the conformation of the polymer backbones. Additionally, how this conformational change affects the electronic and optical properties of polymers will be examined.by Byungjin Koo.Ph. D