Pentacene- and chalcogeneophene-based conjugated compounds as functinonal organic materials

Abstract

Conjugated pi-electron systems have attracted much attention due to their potential application in advanced electronic materials such as light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic photovoltaics (OPV) but also as functional organic compounds capable of two-photon absorption and applicable as nonlinear optics chromophores. The unique electronic properties of organic materials are strongly associated with their pi-electron topology. Alteration of the molecular design of conjugated organic compounds and their functional groups crucially influences electrochemical and photophysical properties (like HOMO/LUMO levels, band gap, quantum yields etc.). Pentacene proved to be a benchmark p-type organic semiconductor, however, its sensitivity to ambient conditions and its low solubility hampers its application in commercial devices. Also, thiophene-based compounds have attracted much attention as advanced electronic materials. Their selenium analogues, selenophene based conjugated pi-electron systems, feature promising materials due to the more electron donating and polarizable selenium. Moreover, selenophenes form more interactive molecular assemblies than their thiophene counterparts. These facts indicate that well-functionalized selenophenes could be utilized as attractive functional materials. However, selenophene-based materials have been little investigated, mainly because of their limited synthetic accessibility. The main goals of the thesis are on the one hand to improve the molecular oxidation stability and solubility of pentacene derivatives by the application of suitable substitutes (e.g. triazoles, isoxazoles and thiophenes) introduced by Copper-catalyzed Azide-Alkyne Huisgen Cycloaddition (CuAAC) or substitution of pentacene-6,13-dione and subsequent reductive aromatization. On the other hand reliable synthetic strategies towards conjugated pi-electron scaffolds based on heteroaromatic moieties (such as triazoles, thiophenes and selenophenes) are presented aiming for improved molecular properties like improved molecular stability, high charge carrier mobility, and enhanced two-photon absorption cross-section. In this context cross-coupling reaction, ring-annulation as well as ring-fragmentation of chalcogenophenes yielding highly conjugated scaffolds are conducted. Moreover, the obtained target compounds are evaluated toward their applicability as functional organic materials.