Macrocycles based on pyrene and ferrocene for molecule-based (spin-)electronics

  • Makrozyklen auf Basis von Pyren und Ferrocen für die molekülbasierte (Spin-)Elektronik

Metzelaars, Marvin; Kögerler, Paul (Thesis advisor); Albrecht, Markus (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

At the core of molecular spintronics is the prospect to surpass conventional materials in information technologies in terms of integration density, energy efficiency, and performance. The realization of molecule-based, (spin-)electronic devices that are of practical relevance requires a solid understanding of the underlying charge transfer/transport processes and the precise engineering of the interactions at the interface between molecules and metal electrodes. The design of novel materials and model compounds is central to meeting these requirements and draws upon the core potential of chemistry to craft molecular structures with well-defined function. Ferrocene and pyrene are two versatile functional groups with unique assortments of properties that justify their application in a large array of different applications. In this thesis, ferrocene and pyrene are utilized as building blocks to construct novel cyclophanes and macrocycles with distinctive structural, optical, chiral, and redox characteristics that are of relevance for the advancement of molecule-based (spin-)electronics. In the first part of this thesis, it is illustrated how chemical design can contribute to the understanding of complex magnetic phenomena at molecule-metal interfaces. The synthesis, characterization, and crystallographic analysis of a pyrene- and ferrocene-based cyclophane is presented. This "pyrenophane" represents a discrete, 3D π-aromatic stack with an interplanar distance of ~3.52 Å and was sublimed onto ferromagnetic Co(111) islands and non-magnetic Cu(111) surfaces. Spin polarized scanning tunneling microscopy (SP-STM) was used at low temperature under ultrahigh vacuum conditions to measure the spin-resolved electron transport efficiency across this pyrenophane and to explore 3D spin interfaces at the molecular level. In the second part of this thesis, I report the one-pot preparation of a chiral, redox active macrocycle that consist of three 2,7-pyrenyl groups that covalently link three 1,1'-ferrocenyl units into a triangle. This novel macrocycle inherits the optical characteristics and π-surface of pyrene and the rotational flexibility and redox behavior of ferrocene. The electron transfer performance within the generated mixed-valence triangle was investigated via electrochemical methods and absorption spectroscopy in solution. Recently, it has been shown that ansa-bridged ferrocene groups show intriguing dynamic conformational changes when integrated into macrocycles. This motivated the investigation of the dynamic chirality of the ferrocene-triangle via variable temperature (VT) NMR experiments and DFT analysis.In the third part of this thesis, it is demonstrated how the modular one-pot approach based on Suzuki-Miyaura coupling that has proven successful in the synthesis of the above mentioned ferrocenyl-pyrenyl cyclophane and triangle can be extended to synthesize gigantic pyrene-based macrocycles. These "pyrenocycles" comprise 2,7-pyrenyl groups that are linked by ortho-phenylene vertices into triangles, squares, envelopes, and figures of eight whose conformers were analyzed by NMR and DFT. In the last part of this thesis, the current literature achievements for the construction of curved aromatic macrocycles are reviewed and DFT calculations aid the critical assessment of synthetic routes toward curved nanobelts and saddles of unprecedented size starting from the synthesized pyrenocycles precursors.

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