Vibrational and electronic spectroscopy of diamondoid cations and their clusters

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Diamondoids are a recently established new class of stable, strain-free, rigid, aliphatic cycloalkanes, representing sp3-hybridized carbon at the molecular nanometer scale. With their unique and strongly variable properties, they are promising building blocks for new nanomaterials with tailored mechanical, electronic, optical, chiral, chemical, and pharmaceutical properties. Variation of these properties is achieved by chemical functionalization, doping, hybrid formation, and solvation, making them candidates for applications in materials and polymer science, molecular electronics, biomedical sciences, and chemical synthesis. Furthermore, diamondoids and nanodiamonds are abundant in interstellar environments, carrying a substantial fraction of cosmic carbon. In many aspects, this novel sp3-based carbon material is complementary to the well-studied sp2 forms graphene and fullerenes, for which Nobel prizes were awarded in physics (2010) and in chemistry (1996). Despite the importance of diamondoid cations, their spectroscopic properties are essentially unknown. However, detailed knowledge of their geometric, electronic, optical, and (bio)chemical properties is required for a deep understanding at the molecular level. To this end, in this renewal project we continue our successful and pioneering initial efforts to characterize the geometric, electronic, optical, chemical, and pharmaceutical properties of simple diamondoid cations, their derivatives and solvated clusters using state-of-the-art laser spectroscopy (IR and optical), mass spectrometry, photoelectron spectroscopy, and quantum chemical methods. Laboratory spectra are required for comparison with astronomical data to improve our understanding of their production in interstellar media and to potentially identify them as carriers of the long known but yet unassigned diffuse interstellar bands and the unidentified infrared emission bands. In addition, the study of derivatives allows for the modulation of their optical and chemical properties. Microsolvation of diamondoid cations with nonpolar and polar ligands sheds light on central properties of these highly reactive intermediates, providing molecular-level insight into reaction mechanisms important for developing novel routes in the organic synthesis and selective functionalization of stable diamondoids and their hybrids. Finally, electronic spectra of diamondoid cations will provide fundamental experimental benchmarks for developing and testing quantum chemical approaches for the reliable calculation of their challenging excited state spectra, which are often complicated by vibronic coupling.