Fullerenes and Caps By Sequential HF Elimination from F-PAHs

Thursday, 28 May 2015: 16:20
Lake Erie (Hilton Chicago)
A. Böttcher, J. Weippert, S. Ulas, P. Weis, J. F. Greisch (Karlsruhe Institute of Technology (KIT)), K. Amsharov (Friedrich-Alexander-Universität Erlangen-Nürnberg), and M. Kappes (Karlsruhe Institute of Technology (KIT))
Appropriately functionalized planar fluorinated polycyclic aromatic hydrocarbons (FPAHs) can be efficiently converted into curved carbon structures via a sequence of thermally activated, regioselective HF elimination steps. [1] On surfaces, such HF elimination is associated with a “planar-to-cap transition” which has been studied by scanning probe methods. [2] The resulting caps have recently been applied to the controlled growth of chirality-selected SWCNTs. [3]  We have studied the mechanism of planar-to-curved conversion  in a variety of active model FPAHs (C26H14F2, C36H15F3 and C60H21F9) using both laser induced desorption (LID) as well electron-impact ionization/heating/fragmentation (EIIHF). For all precursors, we observe sequential HF elimination to be the dominant fragmentation channel. Experiments performed on deposited products of the fragmentation cascade (e.g. C26H12), suggest that the pentagon-hexagon structure of the original FPAH carbon network rearranges during fragmentation. The energy flux deposited into the FPAHs is larger in LID than for EIIHF.  As a result, the sequence of regioselective HF elimination steps can to be taken to completion - to form closed fullerene cages and/or fluorine-free carbon caps depending on the precursor FPAH. By combining LID with ion mobility measurements supported by DFT calculations, we have been able to determine the molecular structure of the (intermediate) fragments along the reaction path thus obtaining insight into the fragmentation mechanism.

[1] M. Kabdulov, et al. Chemistry - A European Journal 19 (2013) 17262

[2] K. Amsharov, et al. Angew. Chem. Int. Ed. 49 (2010) 9392

[3] J.R. Sanchez-Valencia, et al. Nature 61 (2014) 512