Thermal Decomposition of the Fullerene Precursor C₆₀H₂₁F₉ Deposited on Graphite

Abstract

Specially fluorinated polycyclic aromatic hydrocarbons (F-PAHs) are of interest as precursors for transition metal catalyzed CVD growth of chiral-index pure singlewalled carbon nanotubes as well as for the rational synthesis of fullerenes. Laser desorption/ ionization of a prototypical F-PAH has recently been shown to lead to C 60 via a sequence of regioselective intramolecular cyclodehydrofluorination steps: C 60 H on graphite under UHV conditions toward exploring the extent to which such intramolecular dehydrofluorination can also occur on a hot chemically inert surface and to what extent intermolecular interactions influence such transformation processes. C 60 H 21 F 9 films were probed in situ by ultraviolet photoionization, X-ray ionization, Raman spectroscopy, and thermal desorption mass spectrometry, as well as by ex situ atomic force microscopy. Heating multilayer films results first in C 60 H 21 F 9 emission from the bulk (peaked at ∼630 K) followed at higher temperatures by desorption from the interface region (in the range 750−850 K). Sublimation from the interface region is also associated with some on-surface cyclo-dehydrofluorination as indicated by C 60 H 21−n F 9−n , n = 1, 2, 3 emission. C 60 was not observed in the desorbed material suggesting that complete cage closure cannot be achieved on HOPG. Furthermore, C 60 H 21 F 9 deposits cannot be fully removed from HOPG. Instead, competing on-surface polycondensation of reactive intermediates yields a fluorinated carbon phase, which remains stable up to at least ∼1000 K. To complement these studies we have also used mass selective ion beam soft-landing to probe the desorption properties of monodispersed films consisting of mass-selected C 60 H 21−n F 9−n fragments, n = 1, 2.

From Planar to Cage in 15 Easy Steps: Resolving the C60H21F9– → C60– Transformation by Ion Mobility Mass Spectrometry

“…In previous work focusing on the thermal stability of solid C 60 H 21 F 9 , we have demonstrated that up to three of these sequential HFelimination steps can already be induced on-surface simply by heating. 3 Therefore, it is possible that, besides unimolecular fragmentation in gas the phase, on-surface reactions (e.g., as mediated by a previous laser pulse) could also be contributing to the fullerene anion signals observed here. Specifically, recombination of smaller polycyclic fragments either on-surface or in the high density region of the desorption plume might be involved.…”

“…We have recently shown that energization by electron-impact can be used for this purpose. 3 More conventionally, the transformation is activated thermally, e.g., by flash vacuum pyrolysis (in the gas phase) or laser-induced desorption or by heating precursors on (catalytically active) surfaces under ultrahigh vacuum conditions. 4,5 When heating appropriately designed quasiplanar PAH adsorbates on atomically clean flat surfaces, a sequence of such thermally activated on-surface cyclodehydrogenations can lead to increasing curvature and associated strain sufficient to cause carbonaceous caps to form.…”

Combinatorial approach for the synthesis of precursors for chirality-controlled synthesis of SWCNTs

“…Furthermore, after cyclodehydrogenation on a catalyst surface, the respective seed molecules can be elongated a multi‐thousands fold during the SWCNT growth, necessitating only milligram amounts of the respective precursor molecules for the multi‐gram or even kilogram scale production! Taking into account that the present state‐of‐the‐art of MS‐based deposition allows depositing of up to 1 μg of the sample , the gram scale SWCNTs production does not appear to be elusive anymore. In general, the presented synthetic strategy can be further extended to the synthesis of SWCNT precursors for many other chiralities by utilizing various building blocks and other alternative cores.…”

“…As a result of high‐molecular weight such precursors cannot be deposited by molecular beam epitaxy without remarkable decomposition. Nevertheless these difficulties can be overcome by using ion beam deposition . In contrast to molecular beam deposition, mass spectrometric deposition allows not only to deposit extra‐large precursors, but also to perform a post synthetic “purification” of the sample .…”

“…Nevertheless these difficulties can be overcome by using ion beam deposition . In contrast to molecular beam deposition, mass spectrometric deposition allows not only to deposit extra‐large precursors, but also to perform a post synthetic “purification” of the sample . Among various methods suitable for the synthesis of extra‐large PAH molecules, the aldol trimerization of cyclic ketones was found to be very prolific .…”