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. 2017 Jul 20:8:16089.
doi: 10.1038/ncomms16089.

Strain-induced skeletal rearrangement of a polycyclic aromatic hydrocarbon on a copper surface

Akitoshi Shiotari  1 , Takahiro Nakae  2 , Kota Iwata  3 , Shigeki Mori  4 , Tetsuo Okujima  5 , Hidemitsu Uno  5 , Hiroshi Sakaguchi  2 , Yoshiaki Sugimoto  1   3
Affiliations

Strain-induced skeletal rearrangement of a polycyclic aromatic hydrocarbon on a copper surface

Akitoshi Shiotari et al. Nat Commun. .

Abstract

Controlling the structural deformation of organic molecules can drive unique reactions that cannot be induced only by thermal, optical or electrochemical procedures. However, in conventional organic synthesis, including mechanochemical procedures, it is difficult to control skeletal rearrangement in polycyclic aromatic hydrocarbons (PAHs). Here, we demonstrate a reaction scheme for the skeletal rearrangement of PAHs on a metal surface using high-resolution noncontact atomic force microscopy. By a combination of organic synthesis and on-surface cyclodehydrogenation, we produce a well-designed PAH-diazuleno[1,2,3-cd:1',2',3'-fg]pyrene-adsorbed flatly onto Cu(001), in which two azuleno moieties are highly strained by their mutual proximity. This local strain drives the rearrangement of one of the azuleno moieties into a fulvaleno moiety, which has never been reported so far. Our proposed thermally driven, strain-induced synthesis on surfaces will pave the way for the production of a new class of nanocarbon materials that conventional synthetic techniques cannot attain.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Molecular structures of synthesized azulene-derivative PAHs.
(a,b) Calculated structures of diazuleno[1,2-c:2′,1′-g]phenanthrene (DAPh) 1 and diazuleno[1,2-a:2′,1′-c]anthracene (DAA) 2, respectively, in free space. Numbers at carbon atoms were assigned according to the IUPAC nomenclature. Blue spheres in a represent C atoms of one of the azuleno moieties in DAPh 1. (c) Scheme of the adsorption of 1 and 2 onto a Cu(001) surface to modify the molecular geometries.
Figure 2
Figure 2. AFM images and adsorption structures of DAPh and DAA on Cu(001).
(a,b) Typical STM images of DAPh 1 and DAA 2, respectively, on Cu(001) at 4.8 K with CO-terminal tips. (c,d) AFM images of 1 and 2, respectively. (e,f) Schematics of the adsorption structures of 1 and 2, respectively. The nonplanar PAHs are expected to be flattened on the surface. The adsorption sites were determined experimentally (see Supplementary Fig. 2). The image in a was obtained with the sample bias V=−30 mV and the tunnelling current I=10 pA. The image in b was obtained with V=30 mV and I=20 pA. The image in c,d was acquired at the tip height corresponding to V=50 mV and I=200 (20) pA over a bare surface. Scale bars, 10 Å (a,b); 5 Å (c,d).
Figure 3
Figure 3. Thermal reaction of DAPh on Cu(001).
(a–c) Typical STM images of DAPh/Cu(001) at 4.8 K with CO terminal tips after annealing for 10 min at 125, 135 and 205 °C, respectively. The inset of c shows an STM image of a minor product 6. (d) Annealing-temperature dependence of the abundance ratio of the molecular species on the surface. More than 100 molecules were counted at each annealing temperature. The error bar represents the standard deviation from the set-point temperature. The inset of d shows an AFM image of intermediate 3. (e) Reaction of DAPh 1 on Cu(001) to yield a fulvaleno-rearranged product 5 and a naphtho-rearranged product 6 via intermediates 3 and 4. The images were obtained with V=−30 mV and I=10 pA for a, with V=50 mV and I=20 pA for b and the inset of d, and with V=50 mV and I=200 pA for c. The image in the inset of d was acquired at the tip height corresponding to V=50 mV and I=20 pA over a bare surface. Scale bars, 20 Å (a–c); 5 Å (the inset of d).
Figure 4
Figure 4. AFM images of the thermal reaction products of DAPh/Cu(001).
(a–c) AFM images of 4, 5 and 6, respectively, on Cu(001) in constant-height mode with CO-terminal tips. (d–f) Schematic illustration of the adsorption structures of 4, 5 and 6, respectively. All of the products are expected to be flattened on the surface. (g–i) Calculated structures of 4, 5 and 6, respectively, in free space. Blue spheres in g represent C atoms of one of the azuleno moieties in DAPyr 4. A bent red line in g indicates that the sterically hindered azuleno moieties are distorted in free space. The images in a–c were measured at the tip height corresponding to V=50 mV and I=200 pA over a bare surface. Scale bar, 5 Å.
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