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True molecular conformation and structure determination of remarkable polycyclic aromatic hydrocarbons
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ECM33 BOOK OF ABSTRACTS
279
MS39 Crystallography at the nanoscale
MS39-03
True molecular conformation and structure determination of remarkable polycyclic aromatic hydrocarbons
I. Andrusenko 1, E. Mugnaioli 2, M. Gemmi 1, W. Schmidt 3
1Istituto Italiano di Tecnologia, Center for Materials Interfaces, Electron Crystallography - Pontedera (Italy),
2Università di Pisa, Dipartimento di Scienze della Terra - Pisa (Italy), 3PAH Research - Igling-Holzhausen
(Germany)
Abstract
The true molecular conformation and the crystal structure of four large (30 – 46 C atoms) polycyclic aromatic
hydrocarbons (PAHs)1,2 were determined by direct methods from 3D electron diffraction (3D ED)3 data, a result
that could not be achieved by single crystal X-ray diffraction (XRD) due to limited crystal size and the thin leaflet
morphology of the samples. Additionally, three of such compounds were isolated as by-products in the synthesis
of similar materials and, therefore, were available only in very limited amount.
The main strength of 3D ED is the ability to perform single crystal diffraction on sub-micrometric areas. Therefore,
this technique can be used for structure determination when crystal size is the limiting factor for single crystal
XRD. Remarkably, this analytical protocol can be performed even on extremely small sample batches, which
cannot be conveniently prepared for conventional powder XRD.
Moreover, the molecular conformation of two compounds could not be determined via classical spectroscopic
methods due to the large size of the molecules and the occurrence of multiple and reciprocally connected
aromatic rings. On the other hand, 3D ED data provided not only ab-initio structure solution, but also the
unbiased determination of the internal molecular conformation. It is noteworthy that ab-initio crystal structure
determination does not require information about the molecular conformation, but only a rough estimation of the
atomic content of the unit cell.
The other two compounds were synthesised more than 50 years ago, but have hitherto remained structurally
unsolved. All molecules have a considerable interest due to their optoelectronic properties, which led to the
creation of a number of functionalised materials based on PAH backbones. Detailed synthetic routes,
spectroscopic analyses and promising properties are also discussed.
References
1. Hall, C. L., Andrusenko, I., Potticary, J., Gao, S., Liu, X., Schmidt, W., Marom, N., Mugnaioli, E., Gemmi, M.
& Hall, S. R. (2021) 3D Electron Diffraction Structure Determination of Terrylene, a Promising Candidate for
Intermolecular Singlet Fission. ChemPhysChem 22(15), 1631-1637.
2. Andrusenko, I., Hall, C. L., Mugnaioli, E., Potticary, J., Schmidt, W., Gao, S., Marom, N., Hall, S. R. & Gemmi,
M. (2022) True Molecular Conformation and Structure Determination by 3D Electron Diffraction of PAH By-
Products Potentially Useful for Electronic Applications, in preparation.
3. Gemmi, M., Mugnaioli, E., Gorelik, T. E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S. & Abrahams, J. P.
(2019) 3D Electron Diffraction: The Nanoctystallography Revolution. ACS Cent. Sci. 5, 1315-1329
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