Hydrogen-Bonded One-Dimensional Chains of Quinacridone on Ag(100) and Cu(111): The Role of Chirality and Surface Bonding

Abstract

The adsorption and ordering of the prochiral molecule quinacridone (QA) on the Ag(100) and Cu(111) surfaces were studied by low energy electron diffraction and scanning tunneling microscopy. Upon adsorption, the molecules form parallel homochiral chains of flat lying molecules linked together via hydrogen bonds on both surfaces, but these chains show surface dependent significant differences concerning their lateral order. On both substrates, the chains are not thermodynamically stable, but stabilized by kinetic barriers. On the Ag(100) surface, annealing induces a phase transition to a highly ordered and heterochiral structure with a reduced density of hydrogen bonds. This loss of bonding energy is overcompensated by a stronger bonding to the substrate yielding a commensurate structure. For QA on Ag(100), we propose that during the initial chain formation and the phase transition upon annealing, the molecules can change their handedness by rotating around their long axes. In contrast, the initial chain formation and the phase transitions of QA on the Cu(111) surface appear to be subject to stronger kinetic limitations. These are explained by stronger substrate molecule interactions on Cu(111), which reduce the diffusion and the possibility for a change of handedness in comparison to QA on Ag(100). We discuss how the intermolecular hydrogen bonds, the 2D chirality, and the different chemical reactivities of the two surfaces (Ag(100), Cu(111)) influence the structural formation of QA aggregates. We compare our results to results for QA on Ag(111) reported previously by Wagner et al.

Chiral self-organized single 2D-layers of tetramers from a functional donor–acceptor molecule by the surface template effect

“…This is also somewhat unexpected because commensurate structures of large organic molecules typically contain only one or two molecules per unit cell. 34,35 In those situations, the commensurability of the structure can be understood from the preferential adsorption site of the individual molecule. In the present situation, the site is related to a minimum in the interfacial interaction energy of all four constituting HB238 molecules under the restriction of their lateral arrangement within the tetramer.…”

Growth of Hydrogen-Bonded Molecular Aggregates on a Thin Alkali Halide Layer: Quinacridone on KCl/Ag(100)

“…This was already observed for QA on Ag(100), where the correlation in particular decreases with increasing distance between neighboring chains. 12 The analysis of the STM images yields an intermolecular distance within the chains of b 1 = (6.6 ± 0.2) Å. Within the margin of error, this value is identical with the intermolecular distance for QA/Ag(100) in the α-phase, showing that the length of the H-bonds remains unaltered by the insulating KCl layer with respect to the Ag(100) surface.…”

“…Both the fact that the QA molecules are able to diffuse off the KCl islands and the formation of molecular chains and chain-like clusters show that the mobility of QA on KCl at 300 K is high. This is conceivable in view of the small values of E ads of the single QA molecule on the KCl surface, and it fits further to the earlier observation that QA exhibits already a high mobility on the Ag(100) and Cu(111) surfaces, 12 although E ads is larger there. The deduced low Ehrlich-Schwoebel barrier of QA at the KCl/KCl and KCl/Ag(100) steps is also plausible in view of the low E ads of QA on KCl.…”

“…One-dimensional chains of QA have been investigated on Ag(111), Ag(100), and Cu(111), and on graphene and MoS 2 . , These studies have shown that QA does indeed form molecular chains on the named surfaces and that the extended QA structures can be tuned by sample temperature, coverage, or deposition rate. However, since the adsorption and bonding to metal surfaces change the properties of the molecules, the observation of the unperturbed electronic and excitonic states is prohibited there.…”

Two-Dimensional Self-Assembly Driven by Intermolecular Hydrogen Bonding in Benzodi-7-azaindole Molecules on Au(111)

“…Focusing our attention on conjugated molecules, which have gained much relevance due to their use as semiconductors in different electronic applications (organic field-effect transistors, organic light-emitting devices, or organic and hybrid solar cells), their charge transport properties are determined by their intermolecular interactions and their disposition at the substrate interface. − Therefore, the characterization of the molecular arrangement on surfaces provides essential information for the interpretation of material properties and for the development of novel materials. − Scanning tunneling microscopy (STM) becomes a particularly valuable technique for the study of self-assembled nanostructures on surfaces, given the degree of detail that can be reached with molecular or atomic resolution. , In this regard, it is worth highlighting the results reported for hydrogen-bonded conjugated systems with application in the area of organic electronics. Quinacridone has been comprehensively studied on different surfaces such as highly oriented pyrolytic graphite (HOPG), Ag(111), Ag(100), and Cu(111). − Although different degrees of strength in the adsorption of quinacridone have been observed depending on the molecule–substrate interactions, in all cases, homochiral linear structures were observed for each of the expected surface enantiomers. This arrangement results from the complementary hydrogen bonds set between the carbonyl and the NH groups present in the structure of quinacridone.…”