Large organic molecules for quantum interference experiments

Matter-wave dualism is a fundamental concept in quantum physics. The observation of wave properties of heavy organic molecules can be used to approach the borderline between classical and quantum physics. Up to which mass and size do particles or molecules still have wave properties? This question is subject to be answered within this thesis and as part of the international nanoquestfit-project where many researchers of different disciplines are involved.
This thesis is a summary of the work done within a research collaboration between the group of Prof. Dr. Marcel Mayor (University of Basel) and the group of Prof. Dr. Markus Arndt (University of Vienna). The work is mainly focused on the development of novel quantum interference experiments that imply the development of new synthetic strategies towards tailor-made molecules. Novel interferometers have been developed by the Arndt group and therefore the molecular requirements changed strongly within the past years. The syntheses of these tailor-made molecules were performed by the author in the laboratories of Prof. Mayor in Basel. Quantum interference experiments and the preliminary investigations described within this work, namely the thermal stability test, the desorption studies and the laser-induced acoustic desorption have been performed by the Arndt group in Vienna.
Investigations at the interface of quantum and classical physics are a fascinating part of the research. The final goal is to approach the quantum-to-classical transition by the observation of quantum properties of large and complex molecules. In order to study the wave nature of such particles—a purely quantum mechanical phenomenon—synthetic procedures towards tailor-made compounds are developed to improve the observation of this phenomenon through matter-wave experiments.
At the starting point of this work, a series of highly fluorinated porphyrin-monomers set a new benchmark in high-mass quantum interference experiments. The highest masses of particles used in quantum interference experiments were around 10’000 g/mol. Thus, our objective was to reach masses up to 25’000 g/mol with the suitable features for the quantum interferometry experiments.
In the first chapter of this thesis, the principle of interferometry, the development and evolution of this technology are presented. In the subsequent chapters, the different synthetic approaches of the tailor-made molecules designed to improve the measurements and achieve the goal of this thesis are described.
The main part of this thesis is focused on the synthesis of tailor-made molecules for quantum interference experiments. In a first part, the synthesis of a novel, more massive fluorinated phthalocyanine is presented. That phthalocyanine was used in far-field quantum interference experiments. Unfortunately, the molecular requirements could not been tuned to observe wave-particle duality in these experiments. The second part focuses on the synthesis of three different molecular libraries. Molecular libraries are mixtures of molecules having the same core but a to some extent random number of long perfluorinated chains. The individual members within the library were observable in MALDI-TOF mass spectrometry. We attached the chains to three different cores to obtain three different molecular libraries. To produce a first generation of libraries we used diacetylene bond porphyrin-dimer. The rather limited reaction scope of diacetylene bond porphyrins was enhanced by the second generation of tetramers and pentamers. To compare the modularity of the synthesis of oligo-porphyrin systems two additional cores, a porphyrin-dimer and a porphyrin-trimer, have also been synthesized. The possibility to produce a molecular beam with the three molecular-libraries has been investigated by thermal studies, desorption experiments and laser-induced acoustic desorption.
The last part of the thesis is focused on the synthesis of photocleavable tags that can be attached to model compounds. These tags are synthesized since novel quantum interference experiments are based on light gratings where a mass difference is supposed to be observed at the detector level upon cleavage. The final idea is, in the near future, to attach these molecules to large particles, such as metal-nanoparticles, clusters or proteins. It is expected to enable the detection of mass differences of the intact clusters and the clusters with the cleaved tags. Three different model compounds have been synthesized. The cleavage of the tags was proven in solution upon irradiation of UV-light in solution, where a constant and reproducible decay was observed. In future quantum interference experiments, the cleavage should be performed in gas-phase as a final prove of concept. The molecules are currently under investigations in the Arndt group.