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Date of Award

2-2013

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemistry

First Advisor

Sankaran Thayumanavan

Second Advisor

Dhandapani Venkataraman

Third Advisor

Min Chen

Subject Categories

Chemistry | Inorganic Chemistry

Abstract

High temperature anhydrous proton conducting polymer and optoelectronic based organic compounds are promising materials for use in renewable energy applications. Fundamental understanding of better proton and charge transport properties are required to achieve desirable alternative energy materials.

In this thesis, we focus on molecular design, synthetic approaches, and understanding structure-property relationships to improved proton conductivity and optoelectronic properties. In proton conducting polymers, we tethered N-heterocycles (imidazole and benzotriazole) as proton carrier in two polymer systems; dendritic-linear block copolymers and helical polymers. Dendritic-linear block copolymers functionalized with imidazole and benzotriazole are designed to self-organize into nano scale assemblies that would increase local charge density and enhance proton conductivity. We found that microphase separation within disordered structure of imidazole-based block copolymers could relate to the higher conductivity compared to benzotriazole-based block copolymers that do not have phase separation in the same length scale.

In the second system, we have focused on effect of chirality on proton conductivity in helical polymer. We functionalized L-histidine and histamine on poly(phenylacetylene) and poly(4-vinylbenzoate). Poly(phenylacetylene) is known as dynamic helical polymer while poly(4-vinylbenzoate) is a random polymer. Effects of backbone chirality, side chains and doping acids on proton conductivity are evaluated in this work. We found that a single handed conformation of poly(phenylacetylene) bearing L-histidine can enhanced proton conductivity compared to those of containing histamine. Whereas, vinyl backbone, poly (4-vinylbenzoate) bearing L-histidine exhibited lower conductivity due to a higher T g of the polymer.

Cyclopentadithiophene (CPDT) derivatives are often used as an active layer in optoelectronic devices. However, CPDT is known to have a low absorption at the lower energy band. To solve this issue, we proposed to change the conformation of heteroatom at the bridgehead. We incorporated ketone and imine functionalities at the bridgehead positions, anti and syn. We found that by changing heteroatom position to syn-position increased absorption intensity in the lower energy band. Incorporation of a ketone at anti-position provides good mobility of 0.003 cm 2 /Vs while, changing the ketone group at the syn-position significantly decrease charge mobility.

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