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chirality; density functional calculations; hydrogen bonds; photoelectron spectroscopy; scanning probe microscopy
Abstract:
The mesoscale induction of two-dimensional supramolecular chirality
(formation of 2D organic domains with a single handedness) was achieved
by self-assembly of 7,2,4-benzenetricarboxylic (trimellitic) acid on a
Cu(700) surface at elevated temperatures. The combination of
spectroscopic [X-ray photoelectron spectroscopy (XPS) and near-edge
X-ray absorption fine structure (NEXAFS)], real-space-probe [scanning
tunneling microscopy (STM)], and computational [density functional
theory (DFT)] methods allows a comprehensive characterization of the
obtained organic adlayers, where details of molecular adsorption
geometry, intermolecular coupling, and surface chemical bonding are
elucidated. The trimellitic acid species, comprising three functional
carboxylic groups, form distinct stable mirror-symmetric
hydrogen-bonded domains. The chiral ordering is associated with
conformational restriction in the domains: molecules anchor to the
substrate with an ortho carboxylate group, providing two para
carboxylic acid moieties for collective lateral interweaving through H
bonding, which induces a specific tilt of the molecular plane. The ease
of molecular symmetry switching in domain formation makes
homochiral-signature propagation solely limited by the terrace width.
The molecular layer modifies the morphology of the underlying copper
substrate and induces mu m-sized strictly homochiral terraces.
