Nanopatterns of molecular spoked wheels as giant homologues of benzene tricarboxylic acids.

Tristan J Keller,Stefan-S Jester,Markus Bursch,Sigurd Höger,Taria L Schneiders,Joshua Bahr,Theresa Eder,Christopher Sterzenbach,Julia Kohn,John M Lupton,Stefan Grimme

doi:10.1039/d1sc01381e

Tristan J Keller, Stefan-S Jester + Show 9 more

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https://doi.org/10.1039/d1sc01381e

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Abstract

Molecular spoked wheels with D3h and Cs symmetry are synthesized by Vollhardt trimerization of C2v-symmetric dumbbell structures with central acetylene units and subsequent intramolecular ring closure. Scanning tunneling microscopy of the D3h-symmetric species at the solid/liquid interface on graphite reveals triporous chiral honeycomb nanopatterns in which the alkoxy side chains dominate the packing over the carboxylic acid groups, which remain unpaired. In contrast, Cs-symmetric isomers partially allow for pairing of the carboxylic acids, which therefore act as a probe for the reduced alkoxy chain nanopattern stabilization. This observation also reflects the adsorbate substrate symmetry mismatch, which leads to an increase of nanopattern complexity and unexpected templating of alkoxy side chains along the graphite armchair directions. State-of-the-art GFN-FF calculations confirm the overall structure of this packing and attribute the unusual side-chain orientation to a steric constraint in a confined environment. These calculations go far beyond conventional simple space-filling models and are therefore particularly suitable for this special case of molecular packing.

Highlights

Carbon-based structures composed of arylene, arylene–ethynylene, and arylene–butadiynylene units have become prominent target structures in basic research with broad applications in materials as well as medical chemistry,[1,2,3,4] and several outstanding properties of such compounds are manifest.[5]
Degrees of freedom to the otherwise linear segments, sometimes leading to polydispersity regarding conformers.[9]. Such limits can be overcome in strutted architectures, and molecular spoked wheels (MSWs) are prominent examples thereof.7b,10 The lateral xation of molecular rigid backbones on highly oriented pyrolytic graphite (HOPG) can be mediated by a variety of functional groups, such as carboxylic acids as, e.g., in trimesic acid11a,b and its larger homologues.11c,d On the other hand, alkyl/alkoxy side chains show a high affinity to graphite,[12] have an energetically favorable tendency for interdigitating and lead to sufficient compound solubility in common organic solvents
Disk-shaped molecular backbones of a certain size and shape generally require an adequate alkyl/alkoxy proportion in order to keep them soluble, and 3,4,5-trihexadecyloxybenzyloxy groups have been proven as successful substituents for this task as well as for the physisorption of shape-persistent macrocycles (SPMs) and MSWs on HOPG.10g In the latter case, the formation of D6h-symmetric structures is a direct consequence of the synthetic strategies in which either six equal spoke-rimsegments are coupled to a central hub,10a,b,d,f or symmetrical acetylenes are trimerized10g,15 before the rim is closed

Summary

Introduction

Carbon-based structures composed of arylene, arylene–ethynylene, and arylene–butadiynylene units have become prominent target structures in basic research with broad applications in materials as well as medical chemistry,[1,2,3,4] and several outstanding properties of such compounds are manifest.[5]. Scanning tunneling microscopy of the D3h-symmetric species at the solid/liquid interface on graphite reveals triporous chiral honeycomb nanopatterns in which the alkoxy side chains dominate the packing over the carboxylic acid groups, which remain unpaired.

Results

Conclusion