Unbalanced 2D Chiral Crystallization of Pentahelicene Propellers and Their Planarization into Nanographenes

Jan Voigt (1) , Myriam Roy (2) , Miloš Baljozović (1) , Christian Wäckerlin (1) , Yoann Coquerel (3) , Marc Gingras (2) , Karl‐heinz Ernst (1, 4, 5)

1 Empa, Swiss Fed Labs Mat Testing & Res, Dubendorf, Switzerland
2 CINaM - Centre Interdisciplinaire de Nanoscience de Marseille
3 ISM2 - Institut des Sciences Moléculaires de Marseille
4 Nanosurf laboratory, institute of Physics
5 UZH - Universität Zürich [Zürich] = University of Zurich

The chiral self-assembly of trispentahelicene propellers on a gold surface has been investigated in ultrahigh vacuum by means of scanning tunneling microscopy and time-of-flight secondary ion mass spectrometry. The trispentahelicene propellers aggregate into mirror domains with an enantiomeric ratio of 2 : 1. Thermally induced cyclodehydrogenation leads to planarization into nanographenes, which self-assemble into closed-packed layers with two different azimuths. Further treatment induces in part dimerization and trimerization by intermolecular cyclodehydrogenation. Racemic mixtures of chiral molecules crystallize either into racemic crystals with both enantiomers in the crystal unit cell or into a conglomerate of homochiral crystals, that is, a single crystal that contains only molecules of identical handedness. Other possibilities are random distribution of enantiomers, socalled solid solution (or pseudoracemate), [1] or chiral twinning into enantiopure laminates. [2] Although observed for more than [a] J.

Mots clés: graphene; helicenes; on-surface chemistry; polycyclic aromatic hydrocarbons; scanning tunneling microscopy; graphene

Domaines: Chimie organique

Jan Voigt, Myriam Roy, Miloš Baljozović, Christian Wäckerlin, Yoann Coquerel, et al.. Unbalanced 2D Chiral Crystallization of Pentahelicene Propellers and Their Planarization into Nanographenes. Chemistry - A European Journal, 2021, 27 (40), pp.10251-10254. ⟨10.1002/chem.202101223⟩. ⟨hal-03370281⟩