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Projekt Druckansicht

Elektronische Struktur und Dynamik angeregter Zustände von reinen und funktionalisierten Diamantoiden, Diamantoid Aggregaten und Hybriden

Fachliche Zuordnung Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Förderung Förderung von 2010 bis 2017
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 120401550
 
Erstellungsjahr 2017

Zusammenfassung der Projektergebnisse

In this project, the electronic structure and photophysical properties of diamondoids, various diamondoid derivatives as well as diamondoid – metal hybrid particles were studied. (1) The UV absorption and fluorescence emission, as well as the excited state fluorescent rates of pristine diamondoids were spectroscopically investigated. We determined that in these systems, the fluorescent rates scale with particle size, due to the increased number of degrees of vibrational freedom in larger systems. The fluorescence emission spectra were analyzed together with the absorption spectra, in close collaboration with the theory project I. We could determine that the seemingly simple vibrational structure of the diamondoids is much more complex than first expected, and composed of a number of vibrational overtones and population of various vibrational coordinates. For some diamondoids, where the HOMO-LUMO transition is dipole forbidden, relaxation from LUMO to HOMO could be observed in spite of this fact, which promted us to include Herzberg-Teller effects into the spectral analysis. This proved to be a fruitful starting point also for the later analysis of the more complex diamondoid derivatives. (2) A number of diamondoid derivatives (doped diamondoids, functionalized diamondoids and electronically blended diamondoids) were investigated in a fashion similar to the pristine diamondoids, in order to draw conclusions on how these modifications systematically affect the basic electronic properties. In addition, we also analyzed these systems using valence photoelectron spectroscopy, in order to determine their ionization potentials. We could determine that the type of functionalization is the major influence on the ionization potential, while other parameters are less important. For the blended systems, it was determined that the HOMO is always localized to the sp2 hybridized bridge between diamondoid moieties, which is interesting in the context of sp2 impurities in bulk diamond. Investigating the fluorescence, we determined that even though the HOMO-LUMO gap can be tuned as predicted by modifying the diamondoids, strict criteria for when fluorescence occurs apply. In fact, the only type of diamondoid derivative that was found to be a good UV emitter was methylated adamantanes, where quantum yields were even higher than in pristine diamondoids. This is an important stepping stone for tailoring diamondoid systems for future applications. (3) Combining thiolized diamondoids and metal clusters, we performed proof-of-principle experiments where diamondoid – metal cluster hybrids were produced in situ. The photoion yield of these systems was subsequently investigated, and we could determine that the quasi-total fragment ion yield reflects the photodepletion signal perfectly in most cases. This implies that it reflects the proper absorption cross-section, which is a very important result for further investigations using this technique. Primarily, the focus was on investigating aluminium hybrids, due to their predicted plasmonic activity, and on investigating silver and gold hybrids due to their apparent comparability. In the former case, it was determined that already for very small systems, plasmon-like transitions contribute significantly to the overall absorption. For the latter, we found that even though silver and gold are similar in many respects, the hybrid systems behave very differently, with silver showing many discreet states and gold having a more or less continuous absorption in the whole spectral range. Lastly, we have commissioned a 3D ion trap for fluorescence measurements. This set-up provides a range of interesting future possibilities to use the experimental equipment built up during the project duration for direct studies of plasmonic enhancement and quenching effects in well defined gas phase systems. This promises to be an avenue to gain much improved understanding of plasmonic phenomena on the quantum mechanical level, rather than in the macroscopic limit, thereby enabling more efficient design of plasmonic systems than before possible.

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