On-Surface Synthesis of a Nonplanar Porous Nanographene

On-surface synthesis provides an effective approach toward the formation of graphene nanostructures that are difficult to achieve via traditional solution chemistry. Here, we report on the design and synthesis of a nonplanar porous nanographene with 78 sp2 carbon atoms, namely C78. Through a highly selective oxidative cyclodehydrogenation of 2,3,6,7,10,11-hexa(naphthalen-1-yl)triphenylene (2), propeller nanographene precursor 1 was synthesized in solution. Interestingly, although 1 could not be cyclized further in solution, porous nanographene C78 was successfully achieved from 1 by on-surface assisted cyclodehydrogenation on Au(111). The structure and electronic properties of C78 have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy, and scanning tunneling spectroscopy, complemented by computational investigations. Our results provide perspectives for the on-surface synthesis of porous graphene nanostructures, offering a promising strategy for the engineering of graphene materials with tailor-made properties.

S2 meation chromatography (rGPC) purification was performed on JAI HPLC LC 9110 II NEXT with fraction collector FC-3310 and GPC columns 2H and 1H (connected in series), the rGPC was used with HPLC-grade chloroform at room temperature.

Materials
Solvents: Anhydrous solvents (toluene, CH 3 OH, CH 2 Cl 2 ) were purchased from Sigma Aldrich and degassed with Argon before use. Solvents employed for work-up and column chromatography were purchased in HPLC quality and used directly without further purification.
Catalysts and Ligands: Catalysts, ligands and silver salts were purchased from Sigma-Aldrich or Strem and used without further purification.

UV-vis and Fluorescence
The UV-vis spectra were recorded in dichloromethane with concentration of 1.0x10 -5 M at 25 o C. The fluorescence spectra were recorded in dichloromethane with concentration of 1.0x10 -7 M at 25 o C.      Remark: molecule has C 2 symmetry, crystal structure contains probably two molecules CH 2 Cl 2 which were highly disordered -SQUEEZE was used.   Non-contact AFM measurements were performed with a tungsten tip attached to a Qplus tuning fork sensor. 1 The tip was a posteriori functionalized by the controlled adsorption of a single CO molecule at the tip apex from the previously CO-dosed surface. 2 The functionalized tip enables the imaging of the intramolecular structure of organic molecules. 3 The sensor was driven at its resonance frequency (  the wrong decay of the charge density due to the localized basis set. 16 The eigenvalue self-consistent GW calculations were run with the CP2K code on the isolated molecular geometry corresponding to the adsorption conformation. The calculations were performed based on PBE wave functions. We employed the GTH pseudopotentials and analytic continuation with a two-pole model.

X-ray data of 2
The aug-DZVP basis set from Wilhelm et al. 17 was used. To account for screening by the metal surface, we applied the image charge model. 18 To determine the image plane position with respect to the molecular geometry, we used a distance of 1.42 Å between the image plane and the first surface layer, as reported by Kharche et al. 19 DFT band structures of pristine graphene and the porous graphene were calculated with the Quantum Espresso software package using the PBE exchange correlation functional. The plane wave basis with an energy cutoff of 400 Ry for the charge density was used together with PAW pseudopotentials (SSSP 20 ) and a Monkhorst k-mesh of 10 x 10 x 1.