Phase I – Achievements
Phase I – Achievements
During the first funding period, the joint effort and the interdisciplinary interaction between chemists, physicists, materials scientists, chemical engineers and theoreticians involved has proven to be a highly productive and synergistic basis for accomplishing breakthroughs in the field of carbon allotrope research. The overview over some outstanding achievements below documents the effectivity of the broad range of disciplines networking and collaborating at the SFB 953 and shows the pioneering qualities that makes this research program one of the foremost entities of carbon allotrope research in the world.
Both wet-chemical and surface supported approaches have been followed. The highest degree of bulk hydrogenation was obtained in a Birch-type reaction, where frozen water (ice) was used as a gentle proton source. We were able to show, for the first time, that indeed wet chemistry can be used to efficiently generate poly-hydrogenated graphene, which is a milestone achievement on the way to graphane. The reaction product was characterized by statistical Raman spectroscopy and microscopy (SRS, SRM), by IR-spectroscopy, optical spectroscopy (absorption and emission), TGA/MS, and high resolution TEM. For comparison deuterated graphene was also prepared using the same reaction conditions allowing for the unambiguous detection of the expected C-D-vibrations in the respective IR-spectra. The hydrogenated graphene forms a greyish highly fluorescent solid. This indicates rather regioselective hydrogenation with the formation of highly functionalized regions next to isolated islands of intact and fluorescent nanographenes. This assumption is corroborated by HRTEM and also observed in related alkylation reactions. Full single-sided hydrogenation of graphene supported on a surface lead to graphone (single-sided graphane). The thermal stability of the system was investigated with temperature programmed X-ray photoelectron spectroscopy (TP-XPS) and desorption (TPD) and, in conjunction with DFT calculations, a complex coverage dependent hydrogenation and dehydrogenation mechanism was discovered.
The most complete series of extended [n]cumulenes known to date (n = 3, 4, 7, 9) was synthesized. These molecules offer an in-depth analysis of physical, structural, and electronic properties of model compounds for carbyne a new synthetic carbon allotrope. Theoretical aspects of the electronic properties have been unraveled by quantum mechanical calculations and were related to spectroscopic and electrochemical data. The chemical reactivity of new [n]cumulenes has been explored. Next steps towards the formation of stabilized cumulene derivatives involve the prevention of cycloaddition reactions. A general protocol for polyyne and cumulene rotaxanes has been developed, which offers a new stabilization motif for these molecules; likely through preventing intermolecular dimerization. Among the synthesis and characterization of further endcapped carbon-rods, polyynes equipped with pentacene groups represent a particularly interesting class of compounds. Polyyne-pentacene conjugates have been formed, based on di-, tetra-, and hexa-ynes, and explored theoretically and experimentally as molecular wires. Polyynes turned out to provide an ideal molecular wire with a particularly simple vibronic structure in single-molecule experiments. They allowed understanding the all-important interaction of electron motion with vibrations on a single molecule device.