Spontaneous Assembly and Three‐Dimensional Stacking of Antiaromatic 5,15‐Dioxaporphyrin on HOPG

Abstract

Antiaromatic compounds have recently received considerable attention because of their novel properties such as narrow HOMO–LUMO gaps and facile formation of mutual stacking. Here, the spontaneous assembly of antiaromatic meso‐2‐thienyl‐substituted 5,15‐dioxaporphyrin (DOP‐1) is scrutinized at the liquid‐solid interface by scanning tunneling microscopy (STM). Polymorphism in monolayers characterized by the orthogonal and parallel assemblies is found at the low concentration of 0.05 mM. The parallel assembly is more stable and dominantly formed at higher concentrations. Aggregation was observed at concentrations >0.2 mM, and the STM images of the aggregates implied the formation of stacked layers. The intrinsic electronic structures of the mutually stacked bilayer generated by applying an electric pulse to the monolayer were probed by scanning tunneling spectroscopy to reveal the narrowing of the HOMO–LUMO gap by about 20 % compared with the monolayer, thus suggesting significant molecular orbital interactions.

STM Study of the Self-Assembly of Biphenyl-3,3′,5,5′-Tetracarboxylic Acid and Its Mixing Behavior with Coronene at the Liquid–Solid Interface

“…Due to the tunneling requirement of STM, three layers are the maximal stacking that has been reported for the liquid–solid interface condition , although more layers have been revealed under UHV . Recently, bilayer and trilayer structures have attracted much attention because of vertically strong intermolecular interactions and in turn tailored electronic properties such as molecular energy-level splitting and thus reduced band gap. ,− …”