Antiaromaticity, s-Indacene, and Molecular Electronics

Abstract

Almost 100 years ago, the publication of Hückel’s [4n +2] π-electrons rule for identifying aromatic compounds piqued the interest of theorists and experimentalists alike. F. London published his quantum theory of interatomic currents in aromatic compounds, commonly referred to as London diamagnetism only one year later. The idea in a nutshell, is that the delocalized ring current of π-electrons found in aromatic molecules behaves like a conductive metal wire. In the 1950’s R. Breslow, proposed the idea of antiaromatic [4n] π-electron molecules, (formally referred to as pseudo aromatic) as potentially much more conductive molecular wires. Significant developments in synthetic organic chemistry methodology and techniques over the last 75 years have facilitated the study and isolation of a multitude of antiaromatic and aromatic-antiaromatic hybrid molecules. The valuable molecular properties associated with this class of molecules (such as a small HOMO-LUMO gap, amphoteric redox properties, and low energy absorbance) has motivated further investigation due to their potential materials applications in organic electronics. Antiaromatic molecules have maintained a fundamentally interesting status within the chemistry community because they are extremely reactive, difficult to isolate, and possess interesting electronic properties. In this dissertation I will discuss conductive materials composed of organic molecules, conductivity as it applies to molecular circuits, molecular wires, the structure-property relationships of antiaromatic heterocycle-fused-s-indacene derivatives, and the synthesis and study of donor-acceptor heterocycles fused across s-indacene in a set of structural isomers. Chapter I is a historical review of conductive organic materials, electrical conduction in molecular wires, and explanation of the relationship between paratropic ring current strength and diradical character in antiaromatic molecules. Chapter II describes the synthetic methodology of s-indacene derivatives developed by the Haley lab, the effect of heterocycle fusion on the magnetic properties of s-indacene, and rationalization of such based on physical organic principals and the rule of topological charge stabilization. Chapter III details the synthesis and effects of asymmetric donor-acceptor heterocycle fusion on the s-indacene core and explains the potential impact of this work with reference to superconductivity. Chapter IV is a conclusion. This dissertation includes previously published and unpublished co-authored material.