Synthesis of Functionalized Thiophene Based Materials

Functionalized thiophene based materials are promising candidates in many organic electronic applications such as organic field effect transistors, photovoltaic devices, organic light emitting diodes and sensors. Low temperature deposition and solution processing make these materials particularly interesting as their fabrication processes are much less complex than conventional silicon technology. Furthermore, the mechanical flexibility of organic materials makes them well-suited for plastic substrates in light weight and flexible products. Incorporation of different functional moieties can alter the optoelectronic properties of these materials. Attaching stimuli responsive compounds make these materials responsive towards the particular stimulus, and electron donating and withdrawing moieties can be used to tune the HOMO and LUMO energy levels. Spiropyrans are photochromic compounds which shows large structural variation upon absorption of light, and developing new synthetic methodologies to incorporate these units into thiophene based materials via a conjugated pathway is crucial in order to study the effect of photochromism on optoelectronic properties of a conjugated material. Functionalization of thiophene based materials with alkoxy substituents raise the HOMO level of the materials and thus lower the band gap. Application of alkoxy substituted polythiophene on organic electronic devices can demonstrate how charge transportation of the material is affected by the substituent.

Chapter 1 discusses the thiophene based conjugated materials and their electronic properties including band structure, conductivity and charge transport mechanism. The operation mechanism of organic field effect transistors and effect of functionalization of thiophene based materials with photochromic spiropyrans and alkoxy groups with respect to organic electronic applications is discussed.

Chapter 2 demonstrates development of synthetic methodologies to incorporate photochromic spiropyran as a backbone unit into thiophene based polymers via a conjugated pathway.

Chapter 3 illustrates a new synthetic method to incorporate photochromic spiropyran substituents as pendent groups to thiophene repeat units through a conjugated pathway.

Chapter 4 discusses the synthesis of triethylene glycol monomethyl ether substituted polythiophene, optoelectronic properties and the charge carrier mobility with field-effect transistors and in Schottky diode. It also describes the applicability of doped polymer as an alternative to commercially available PEDOT: PSS.