Nanoobjects microscopy

Rotational polymorphism in monolayers of diamondoids
Lopatina Ya.Yu.1, Zhuk T.S.2, Fokin A.A.2, Marchenko A.A.1
1 Department of Physical Electronics, Institute of Physics of NAS of Ukraine. Nauky ave, 46, Kyiv-03039, Ukraine.
E-mail: yaroslava.lopatina@gmal.com
2 Department of Organic Chemistry, National technical university of Ukraine “KPI”, Peremohy ave, 37, Kyiv-03056, Ukraine.

In recent years the thiolation of diamondoids has proved to be a successful method to apply their unique properties [1,2]. However, terminal groups can change electronic structure of molecules [3], which raises the question of the impact of functionalization. To elucidate this effect on self-assembly on Au(111) surface we chose two diamantane thiol derivatives with SH-group attached either to apical (4) or medial (1) position of the hydrocarbon cage (Fig.1,insets). The structure of monolayers was observed using scanning tunneling microscopy (STM).
It has been revealed that Dia-1-SH molecules (Fig.1,b) may form hexagonal (A), rectangular (B) and “flower” (C) structures, while for Dia-4-SH only hexagonal packing is observed (Fig.1,a). The difference is caused by the position of SH-group that affects the S-Au-bond symmetry of molecule (rotational polymorphism).

Fig.1. STM-images of diamantane-4-thiol (a) and diamantane-1-thiol (b) monolayers on Au(111) surface. Scanning area: 10×10 nm2.
1.	Yan H. et al. Monochromatic photocathodes from graphene-stabilized diamondoids // Nano Lett. – 2018. – 18(2). – P.1099-1103.
2.	Yan H. et al. Hybrid metal–organic chalcogenide nanowires with electrically conductive inorganic core through diamondoid-directed assembly // Nature materials. – 2017. – 16. – P.349-355.
3.	Rander T. et al. Electronic structure tuning of diamondoids through functionalization // J. Chem. Phys. – 2013. – 138. – P.024310.