Controlling the Photophysics, Photochemistry and Solid-State Geometry of Organic Semiconductors with Side Chain - Main Chain Interactions

• Main Author: Pawle, Robert H
• Format: Dissertation
• Language: English
• Subjects: chemistry, inorganic; chemistry, organic
• ISBN: 1303987058; 9781303987052

Conjugated organic materials combine the material properties of plastics with the electronic and optical properties of inorganic semiconductors. While their performance and useful lifetime still lags behind inorganic materials, they represent an attractive alternative due to their low cost, material flexibility and low toxicity. While a large amount of progress has been made in the understanding of these materials and the molecular architecture that controls their optical properties, these studies overwhelmingly focus on the conjugated main chain. Side chains, which impart solubility to conjugated materials, are often viewed as necessary to achieve the favorable materials characteristics but orthogonal to material electronic properties. This research describes the use of side chains as a tool to complement main chain electronic structure, add material functionality, and control solution and solid state optoelectronic properties.
Chapter 2 illustrates the use of non-conjugated side chains to tune the material band gaps. We show that by using terephthalate ester groups as a component of main chain architecture, the band gap of the resulting polymer is sensitive to the inductive nature of the ester alkoxy group. Furthermore, we provide a method to predict the band gap shift a specific alkoxy group will yield.
Chapter 3 describes the use of side chains to control material emissive properties and solubility with light. Installing a photocleavable quenching group onto the material main chain results in a material that responds to irradiation with increased fluorescence. Additionally, the photocleavage reaction results in an acid group on the main chain. Deprotonation of the acid results in an insoluble material. Finally, we show that the control over solubility can be expanded to polymer systems.
Chapter 4 shows that aromatic substituents can control solid state molecular packing. Through the use of aromatic-aromatic side chain\main chain interactions, the planarity of the material main chain can be controlled, resulting in either highly planar main chains or highly twisted main chains, depending on the nature of the aromatic side chain group. These contrasting main chain architectures result in optical transitions that are either more energetic or less energetic than the corresponding solution state properties.