Self-assembly of three-dimensional molecules is scarcely studied on surfaces. Their modes of adsorption can exhibit far greater variability compared to (nearly) planar molecules that adsorb mostly flat on surfaces. This additional degree of freedom can have decisive consequences for the expression of intermolecular binding motifs, hence the formation of supramolecular structures. The determining moleculesurface interactions can be widely tuned, thereby providing a new powerful lever for crystal engineering in two dimensions. Here, we study the self-assembly of triptycene derivatives with anthracene blades on Au-( 111) by Scanning Tunneling Microscopy, Near Edge Xray Absorption Fine Structure and Density Functional Theory. The impact of molecule-surface interactions was experimentally tested by comparing pristine with iodinepassivated Au(111) surfaces. Thereby, we observed a fundamental change of the adsorption mode that triggered self-assembly of an entirely different structure.

Self-assembly of supramolecular monolayers at liquid–solid interfaces has matured into an established research field. Numerous studies unveiled crucial influences of solvent, solute concentration, and temperature on the kinetics and thermodynamics of monolayer formation and their specific role for structure selection. Yet, almost all experiments are carried out on highly inert graphite surfaces that are straightforward to prepare. However, the strong focus on graphite leaves the crucial impact of the underlying surface severely underexplored. Here, we show that passivation of Au(111) with a chemisorbed monolayer of iodine atoms renders it sufficiently inert for studies at liquid–solid interfaces, even at elevated temperatures. By using aromatic homologues of benzene tricarboxylic acids as a well-explored model system and by a one-to-one comparison to graphite, we unveil that molecule–surface interactions can cause substrate-induced polymorphism, crucially affect the supramolecular monolayer’s thermodynamic stability, or even result in the emergence of new polymorphs. These experiments underscore a decisive and specific thermodynamic influence of the underlying surface. We expect our study to stimulate further research on the surface influence on interfacial monolayers by employing this accessible and easy-to-prepare surface with the aim to establish a new lever for steering supramolecular self-assembly.

Die Selbstassemblierung dreidimensionaler Moleküle auf Oberflächen ist bislang kaum untersucht. Ihre Adsorptionsmodi können im Vergleich zu (nahezu) planaren Molekülen, die meist flach auf Oberflächen adsorbieren, eine viel größere Variabilität aufweisen. Dieser zusätzliche Freiheitsgrad kann entscheidende Konsequenzen für die Ausprägung intermolekularer Bindungsmotive und damit für die supramolekulare Strukturbildung haben. Dabei ist es möglich die bestimmenden Molekül‐Oberflächen‐Wechselwirkungen über weite Bereiche einzustellen, was einen neuen, wirkmächtigen Hebel zur Steuerung der Kristallisation in zwei Dimensionen darstellt. Hier untersuchen wir die Selbstassemblierung von Triptycen‐Derivaten mit Anthracen‐Einheiten auf Au(111) mit Hilfe der Raster‐Tunnel‐Mikroskopie, der Röntgen‐Nahkanten‐Absorptions‐Spektroskopie und der Dichte‐Funktional‐Theorie. Der Einfluss von Molekül‐Oberflächen‐Wechselwirkungen wurde experimentell durch den Vergleich von reinen mit Jod‐passivierten Au(111) Oberflächen untersucht. Dabei beobachteten wir eine grundlegende Änderung des Adsorptionsmodus, die zur Selbstassemblierung einer grundlegend verschiedenen Struktur führte.