Novel tailor-made externally triggerable single-molecular switches for molecular electronics

Abstract

Molecular electronics marks a highly interdisciplinary scientific field, in which physicists, chemists, and biologist jointly investigate electronic phenomena on a molecular level. Herein, the foremost task of the chemist is the design and synthesis of novel, tailor-made model compounds bearing externally addressable or controllable functions, which are predominantly of electronic nature. This present PhD thesis mainly focusses on the synthetic aspects towards innovative metalorganic coordination complexes, in particular those containing iron(II) species as the central metal ion. One of the very unique properties of iron(II) ions is their potential capability of switching their spin state between a low-spin and a high-spin form. It represents the general, overall target of this work to externally address and control these potential spin switching properties of the incorporated iron(II) centers and to, therefore, create molecular switching entities addressable on a single molecular level. On the pathway towards the ultimate miniaturization of electronic components such single molecular spin switching entities represent one of the inevitable key components. Chapter 1 provides an introduction of the variety of scientific fields, which are of relevance to the work described within this thesis. Herein, at first the field of molecular electronics is introduced by addressing methods used to contact single molecules, important features of molecular charge transport, properties and important previous examples of single molecular switches, and finally by giving a sufficient background about the spin crossover phenomenon. Hereafter, syntheses and applications of terpyridines and their metal complexes are discussed, prior to giving a brief introduction about aryl-aryl bond formation reactions, representing a key task of the synthetic work described throughout this thesis. Finally, with regard to one of the main objectives of this work an introduction is given about azobenzenes and their incorporation into macrocyclic assemblies. Chapter 2 plainly delivers a profound description of the main aims of this PhD work. Chapter 3 describes the molecular design, synthesis, and physical investigation of a new class of electrically addressable, single molecular spin switches relying on the coordination sphere dependent spin state of hexa-coordinate iron(II) bis(terpyridine) complexes. Chapter 4 describes molecular design, synthesis, and physical investigation of a mechanically addressable, single molecular spin switch once more relying on the coordination sphere dependent spin state of hexa-coordinate iron(II) bis(terpyridine) complexes. Chapter 5 describes the conceptual design and synthesis towards optically addressable, molecular switching metalloazobenzenophanes, representing macrocycles including a photosensitive azobenzene moiety in the molecular backbone in addition to a potentially spin-switching iron(II) core ion. Chapter 6 summarizes the present work and gives a brief outlook. Chapter 7 provides experimental details as well as a full characterization of all the compounds described throughout this thesis.