On-Surface Hydrogenation of Buckybowls: From Curved Aromatic Molecules to Planar Non-Kekulé Aromatic Hydrocarbons

Abstract

Functionalization of surfaces with derivatives of Buckminsterfullerene fragment molecules seems a promising approach towards bottom up fabrication of carbon nanotube modified electrode surfaces. The modification of a Cu(100) surface with molecules of the buckybowl pentaindenocorannulene has been studied by means of scanning tunneling microscopy, carbon monoxide-modified non-contact atomic force microscopy, time-of-flight secondary mass spectrometry and quantum chemical calculations. Two different adsorbate modes are identified, in which the majority is oriented such that the bowl cavity points away from the surface and the convex side is partially immersed into a fouratom vacancy in the Cu(100) surface. A minority is oriented such that the convex side points away from the surface with the five benzo tabs oriented basically parallel to the surface. Thermal annealing leads to hydrogenation and planarization of the molecules in two steps under specific C-C bond cleavage. The benzo tabs of the convex side up species serve as hydrogen source. The final product has an open shell electron structure that is quenched on the surface.

On‐Surface Hydrogen/Deuterium Isotope Exchange in Polycyclic Aromatic Hydrocarbons

“…[35] Consistent with previous in situ SIMS studies, SIMS induced hydrogenation is not observed. [13,20] After annealing in D 2 gas, Figure 1 a), shows that superhydrogenation (i.e. formation of C 24 {H,D} n with n > 12), as observed in case of exposure to atomic hydrogen, [36,37] does not occur.…”

“…+ peaks with integer n originate from intact GNR oligomers and that they do not originate form the SIMS induced fragmentation of longer GNRs. The low intensity half-integer n signals themselves may originate from the presence of a minor bromoanthracene impurity in the DBBA starting material or from rarely occurring CÀC bond breaking [20] induced by atomic hydrogen released during cyclodehydrogenation. An improbable SIMS-induced fragmentation pathway of longer GNRs can also not be excluded.…”

“…[11][12][13] Although atomic hydrogen on coinage metal surfaces desorbs already below room temperature by recombination to H 2 , [14,15] it can induce reactions such as desorption of Br as HBr, [11,13,16] undesired passivation of the active sites in on-surface polymerization, [16,17] cleavage of cyano groups as HCN, [18] conversion of surface copper oxide to water [19] or CÀC bond cleavage and hydrogenation. [20] Externally produced atomic hydrogen has been used to selectively deactivate active sites in on-surface polymerization chemistry, [21] to deliberately clean-up Br, [21,22] and to induce C À C coupling. [23] Despite the nobleness of gold, [24] its surface has the ability to dissociate H 2 , most likely at undercoordinated Au atoms.…”

On‐Surface Hydrogen/Deuterium Isotope Exchange in Polycyclic Aromatic Hydrocarbons

“…Many important reactions, such as cyclodehydrogenation chemistry or metalation reactions, yield adsorbed atomic hydrogen [11–13] . Although atomic hydrogen on coinage metal surfaces desorbs already below room temperature by recombination to H 2 , [14, 15] it can induce reactions such as desorption of Br as HBr, [11, 13, 16] undesired passivation of the active sites in on‐surface polymerization, [16, 17] cleavage of cyano groups as HCN, [18] conversion of surface copper oxide to water [19] or C−C bond cleavage and hydrogenation [20] . Externally produced atomic hydrogen has been used to selectively deactivate active sites in on‐surface polymerization chemistry, [21] to deliberately clean‐up Br, [21, 22] and to induce C−C coupling [23] …”

“…[35] Consistent with previous in situ SIMS studies, SIMS induced hydrogenation is not observed. [13,20] After annealing in D 2 gas, peaks at higher masses appear. With further annealing in D 2 gas, this comb of peaks shifts further to higher masses and finally narrows down around a main peak at 312.2 u, that is, at 12.1 u higher mass than the original CR signal, evidencing H (1.0078 u) !…”