Metal

Gene

Adsorption

Phase (matter)

Chemical physics

Metallurgy

Materials science

Gibbs isotherm

Polymorphism (computer science)

Biochemistry

Molecule

Physical chemistry

Nanotechnology

Organic chemistry

Mathematics

Interface (matter)

Genotype

Geometry

Monolayer

Scanning tunneling microscope

Crystallography

Chemistry

Hydrogen bond

The Journal of Physical Chemistry C

Polymorphism of organic molecular materials plays a prominent role in organic (opto)electronic devices, where the structural properties of metal/organic interfaces determine performance-critical parameters such as charge carrier injection rates. Here, we show that (sub)monolayers of a 2D-prochiral aromatic dinitrile with a bent quaterphenyl backbone engage in pronounced polymorphism on a Ag(111) surface and form a unique phase with alternating polar orientation of the molecules. In the saturated monolayer, the molecules are nearly coplanar with the substrate (flat-lying) and form an ordered racemic structure consisting of chiral dimers stabilized by H···NC hydrogen bonds. At submonolayer coverages, two ordered phases coexist with a dilute mobile phase. One phase forms homochiral domains with a quasi-Kagome structure. The other phase has a unique structure consisting of alternating rows of flat-lying and upright-standing molecules. The two different polar orientations can be distinguished by scanning tunneling microscopy. The upright-standing molecules have a straight and brighter shape and show increased packing density compared to their flat-lying counterparts. These results reveal the great local variability of molecular arrangements at metal/organic interfaces, even for fixed global parameters such as temperature and coverage.

Polymorphism at the Metal/Organic Interface: Hybrid Phase with Alternating Coplanar and Vertical Adsorption Geometry