Piecing Together Large Polycyclic Aromatic Hydrocarbons and Fullerenes: A Combined ChemTEM Imaging and MALDI-ToF Mass Spectrometry Approach

Abstract

Motivated by their importance in chemistry, physics, astronomy and materials science, we investigate routes to the formation of large polycyclic aromatic hydrocarbon (PAH) molecules and the fullerene C60 from specific smaller PAH building blocks. The behaviour of selected PAH molecules under electron (using transmission electron microscopy, TEM) and laser irradiation is examined, where four specific PAHs—anthracene, pyrene, perylene and coronene—are assembling into larger structures and fullerenes. This contrasts with earlier TEM studies in which large graphene flakes were shown to transform into fullerenes via a top-down route. A new combined approach is presented in which spectrometric and microscopic experimental techniques exploit the stabilisation of adsorbed molecules through supramolecular interactions with a graphene substrate and enable the molecules to be characterised and irradiated sequentially. Thereby allowing initiation of transformation and characterisation of the resultant species by both mass spectrometry and direct-space imaging. We investigate the types of large PAH molecule that can form from smaller PAHs, and discuss the potential of a “bottom-up” followed by “top-down” mechanism for forming C60.

Time resolved growth of (N)-polycyclic aromatic hydrocarbons in engine deposits uncovered with OrbiSIMS depth profiling

“…The presence of 5-membered PAHs also opens the possibility of formation of curved PAHs or fullerenes since the strained 5-membered ring causes curvature in the PAH structure. 19,20 We found low intensity peaks corresponding to molecular ions for the smallest fullerenes, C 24 + and C 28 + , in injector tip 2, 5 and 8 (Fig. S13†).…”

“…strained 5-membered ring causes curvature in the PAH structure. 19,20 We found low intensity peaks corresponding to molecular ions for the smallest fullerenes, C 24 + and C 28 + , in injector tip 2, 5 and 8 (Fig. S13 †).…”

“…18 Flat and curved PAHs can form from smaller PAHs and can go onward to form soot particles and their mechanisms of formation have been well studied. [19][20][21] To advance this work we propose the use of the 3D OrbiSIMS depth profiling function to analyse deposits in situ on fuel injector component surfaces to establish the fate of molecules once deposited on a surface. This technique combines a low energy gas cluster ion beam to generate relatively large diagnostic secondary ions in situ for accurate identification and confirmation using the high mass resolving power (>240, 000) and MS/MS (fragmentation/structural characterization) capability of the Orbitrap™.…”

“…18 Flat and curved PAHs can form from smaller PAHs and can go onward to form soot particles and their mechanisms of formation have been well studied. 19–21…”

Laser Desorption Ionization of Large Condensed Polycyclic Aromatic Hydrocarbons in Petroleum Pitch and Thermally Treated Products

“…One speculation is that some of the trimers may be consumed to form the fullerenes. In a recent work on fullerene formation, Gover et al 29 proposed a "bottom-up" followed by "top-down" mechanism, involving the aggregation of smaller PAH molecules to form oligomers, followed by ejection of carbons and hydrogens. The so-called "Stone−Wales" rearrangements 30 of bonds are required to form five-member-ring moieties and produce the stable fullerene structure.…”