Synthesis and characterization of triangulene

Abstract

* These authors contributed equally to this workTriangulene, the smallest triplet ground state polybenzenoid (also known as Clar's hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized isomers (2, also denoted as dihydrotriangulenes) as precursor molecules. Compound 2 was deposited on Cu(111), NaCl(100), and Xe(111) surfaces to generate triangulene (1) by means of atomic manipulation. STM/AFM is an ideal combination to study on-surface synthesis ranging from individual molecules 9, 10 to graphene nanoribbons 11,12 . The chemical structure of reactants and products can be resolved by means of AFM with functionalized tips 13 . Even molecules too elusive to be studied by other means 14,15 can be stabilized by using an ultrathin insulating film as a decoupling 2 layer. A decoupling layer also facilitates studying the frontier molecular orbitals of the free molecule by means of STM and scanning tunnelling spectroscopy (STS) 16 .Figure 2 presents STM and AFM images of four different molecular species of compound 2 adsorbed on NaCl. As expected, different isomers of dihydrotriangulene are observed. This observation can be discussed by a comparison of Fig. 2e and Fig. 2f, showing the non-equivalent isomers 2a and 2b which we found on the surface, respectively. Because the former isomer is prochiral with respect to adsorption, we also observed its surface enantiomer (see Supplementary Fig. 5). Note that 2a is about three times more abundant than the highly symmetric 2b, although two Clar sextets can be drawn for both species. This difference can be rationalized by the resonance energy of its aromatic Remarkably, the ketone 3 in Fig. 2g represents an oxidized structure of 2 that was already reported by Clar and Stewart 1. A comparison of STM and AFM data reveals that in the STM images a tiny sharp kink arises at the position of a single CH 2 group. In contrast, a ketone group leads to a fainter bulge in STM images (Figs. 2c, d) and a lower contrast of the hexagon involved. The central carbon of the three adjacent CH 2 group in 3 adopts the expected tetrahedral bond angle for sp 3 carbon leading to sharp ridges in both STM and AFM mode (Figs. 2c, g) because of strong tilting of the CO molecule at the tip apex.We dehydrogenated promising candidates (2a and 2b molecules) to obtain triangulene by means of atomic manipulation 14,15,19 . To this end, we first positioned the tip above a molecule. Then, we opened the feedback loop and retracted the tip by 0.5 to 0.7 nm to limit the tunnelling current to a few picoamperes. Finally, we increased the voltage to values ranging from 3.5 to 4.1 V for several seconds. In many cases, this procedure also resulted in a lateral displacement of the molecule. When a subsequent STM image indicated a change in the appearance of the molecule, we recorded AFM 3 images to obtain its structure. Using this procedure, we did not observe any changes in the molecular structure other than the removal of single hydrogens from a CH 2 groups throughout our experiment...

Direct Formation of C−C Triple‐Bonded Structural Motifs by On‐Surface Dehalogenative Homocouplings of Tribromomethyl‐Substituted Arenes

“…[1][2][3][4] As ar esult, many unexpected reactions have been achieved on different surfaces. [10][11][12][13][14] Remarkably,the formation of acetylenic scaffolds (i.e., sphybridized carbon structures) has been attempted on surfaces, and has been advanced recently. [10][11][12][13][14] Remarkably,the formation of acetylenic scaffolds (i.e., sphybridized carbon structures) has been attempted on surfaces, and has been advanced recently.…”

Rasterkraftmikroskopie für die molekulare Strukturaufklärung

“…Ein jüngstes Beispiel ist die erste Synthese eines unsubstituierten Tr iangulens.Z wei molekulare Vorstufen (Abbildung 8a) wurden auf Cu, NaCl und Xe zum Tr iangulen (Abbildung 8b) dehydriert. [131] Grund dafürsind mçglicherweise die ungepaarten Elektronen des Moleküls,d .h.s ein p-radikalischer Charakter. Clar und Steward versuchten zum ersten Mal 1953, dieses Molekülz usynthetisieren, [130] aber bislang mussten immer Seitengruppen zur Stabilisierung eingeführt werden.…”

“…Abdruck von (b) mit Genehmigung von Macmillan Publishers Ltd:Nature Chemistry,[131] Copyright 2017. a) Das Triangulen wurde hergestellt, indem aus der molekularen Vorstufe zwei Wasserstoffatome durch Spannungspulse aus der Spitze entfernt wurden.…”

Elusive triangulene created by moving atoms one at a time

“…They then used two successive voltage pulses from the tip, carefully positioned above the molecules, to blast off two hydrogen atoms and create the unpaired electrons. The work is published in Nature Nanotechnology 1 .…”