Defect-Induced π-Magnetism into Non-Benzenoid Nanographenes.

Kalyan Biswas,Koen Lauwaet,José M Gallego,Ana Sánchez-Grande,José I Urgel,Rodolfo Miranda,Xinliang Feng,Ji Ma,David Écija,Lin Yang,Qifan Chen,Pavel Jelínek

doi:10.3390/nano12020224

Abstract

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) on the Au(111) surface. A1 and A2 contain two five- and one seven-membered rings within their benzenoid backbone, while A3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

Highlights

Introduction published maps and institutional affilThe physicochemical properties of well-defined compounds that consist of fused conjugated aromatic rings, frequently referred as to polycyclic aromatic hydrocarbons or NGs [1], have been under the spotlight over the last years due to their potential in great number of technological applications [2,3,4]
We report the synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) with a total spin (S) = 1/2 in their atomic lattice, resulting from the on-surface and A3 ) with a total spin (S) = 1/2 in their atomic lattice, resulting from the on-surface reactions of the 10,10′-bis(2,6-dimethylphenyl)-1,1′-dimethyl-9,9′-bianthracene precursor reactions of the 10,100 -bis(2,6-dimethylphenyl)-1,10 -dimethyl-9,90 -bianthracene precursor (P) on Au(111) in a UHV environment (Scheme 1)
Since the synthesis of E through conventional solution synthesis methods was unsuccessful, we directed our attention to the on-surface synthesis approach

Summary

Experimental Details

Experiments were performed in a custom-designed ultra-high vacuum system (base pressure below 4 × 10−10 mbar) hosting a commercial low-temperature microscope with STM/AFM capabilities from Scienta Omicron and located at IMDEA Nanoscience (Madrid, Spain). All STM images shown were taken in constant-current mode, unless otherwise noted, with electrochemically etched tungsten tips, at a sample temperature of 4.3 K (LakeShore, Carson, CA, USA). TCE-BSC, Seelze, Germany) onto the clean Au(111) surface held at room temperature with a typical deposition rate of 0.5 Å/min (sublimation temperature of 170 ◦ C), controlled by a quartz micro balance (LewVac, Burgess hill, United Kingdom). After deposition of P, the sample was post-annealed at 200 ◦ C for 10 min to induce the cyclodehydrogenation reaction. The sensor was driven at its resonance frequency (~26 kHz for Qplus) with a constant amplitude of ~80 pm. The shift in the resonance frequency of the sensor (with the attached CO-functionalized tip) was recorded in a constant-height mode (Omicron Matrix electronics and MFLi PLL by Zurich Instruments (Zurich, Switzerland) for Omicron). WSxM 5.0 (Madrid, Spain) [41]

On-Surface Synthesis of Non-Benzenoid Nanographenes

Electronic and Magnetic Characterization of Non-Benzenoid Nanographenes

NGs and

Conclusions