Mass spectrometric study of chemical reactions, molecular migrations, and interactions in dynamic organic systems

Molecular interactions, recognition, and self-assembly are of central importance for the properties of organic materials and function of biological systems. Currently, there is no experimental method available that allows inter-molecular interactions to be probed at the scale of single molecules in non-crystalline organic matter. Often, molecular aggregation, self-assembly at single-nanometer scales, and nucleation processes remain beyond experimental reach. The presented work demonstrates that statistical molecular interaction probabilities, surroundings, and arrangement can be probed in-situ in organic matter by means of secondary ion mass spectrometry. Supramolecular assemblies containing 10 and more organic molecules linked by hydrogen bonds or dipole-pi interactions are extracted under preservation of chemistry and structure. The compositional distributions of the assemblies extracted reveal molecular self-assembly at length-scales typically not accessible to electron microscopy or X-ray diffraction.
In dynamic organic systems, shifts in the spatial distributions of the different molecules can induce changes in the local chemical equilibria at nanometer lengthscales. Work conducted in this thesis on thin-film organo-electronic devices with sub-100 nm layer thicknesses demonstrates that molecular distribution rearrangements and the resulting adjustments in chemical equilibira can be resolved in time by means of dual-beam depth profiling in secondary ion mass spectrometry and with sufficient depth resolution to resolve the interfacial formation of electric double-layers. The presented approach for the in-situ study of dynamical systems, while limited to thin-film electronics, provides insight into reversible field-induced molecular migrations and chemical processes where until now often only indirect information could be gained by means of e.g. capacitance measurements.