ICYS Annual Report 2023

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ICYS Annual Report 20231. Outline of Research2. Research ActivitiesKewei SUNFig.1. The scheme of on-surface synthesis.Fig. 2. (A) On-surface synthesis of Si incorporated COFs with C4Si2 rings. (B) On-surface synthesis of nanographene with C4Si rings and nanoribbons with C6Si2 rings.Reference1) L. Grill ,  S. Hecht , Nat. Chem. 2019, 12, 115-130.2) L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 2009, 325, 1110-1114.3) K. Sun, D. Li, T. Kaihara, S. Minakata, Y. Takeda, S. Kawai, Commun. Chem. 2023, 6, 228.4) K. Sun, K. Sugawara, A. Lyalin, Y. Ishigaki, K. Uosaki, O. Custance, T. Taketsugu, T. Suzuki, S. Kawai, ACS Nano 2023, 17, 24355-24362.5) X. Xu, K. Sun, A. Ishikawa, A. Narita, S. Kawai. Angew. Chem. Int. Ed. 2023, 62, e202302534.6) K. Sun, O. Silveira, Y. Ma, Y. Hasegawa, M. Matsumoto, S. Kera, O. Krejčí, A. Foster, S. Kawai, Nat. Chem. 2023, 15, 136-142.7) K. Sun, L. Kurki, O. J. Silveira, T. Nishiuchi, T. Kubo, A. S. Foster, S. Kawai. Angew. Chem. Int. Ed. 2024, 63, e202401027.Low-dimensional carbon-based advanced nanomaterials and functional nanostructures are viewed as one of main candidates for application in next-generation nano-electronics. Their electronic properties can be tuned with the different sizes, shapes and structures. On-surface synthesis that has been developed in past decade is an advanced technique to fabricate various carbon nanostructures with atomic precision by chemical reactions on metal surfaces.1) Molecules can react with each other to form various nanostructures, which are induced by underlying metal substrates, light and injected electrons, as shown in Fig. 1. A lot of advanced nanostructures have been successfully fabricated by such as nanographenes, graphene suitable precursors, nanoribbons (GNRs) and surface covalent organic frameworks.Scanning tunneling microscopy (STM)/atomic force microscope (AFM) is a powerful tool to characterize the atoms, molecules tip and nanostructures on surfaces. In particular, STM functionalized by a small carbon monoxide (CO) molecule enables us to observe inner structure of single molecule.2) Moreover, the STM/AFM tip even can induce the local chemical reaction due to the injected electrons, such as 0D cyclo[18]carbon molecule, 2D carbon allotrope with four, six and eight membered rings. Hence, the resolution at chemical bond level dramatically application of STM/AFM facilitates characterization in on-surface reactions.Now, I am concentrating on the fabrication of low-dimensional carbon-based nanomaterials with atomic precision on solid surfaces through chemical reactions. Additionally, I am involved in the characterization of their physical and chemical properties using scanning tunneling microscopy/spectroscopy (STM/STS). This research holds significant importance as atomically accurate carbon-based nanostructures are considered valuable materials for potential applications in future nanoelectronics. Fabricating these nanostructures proves challenging through methods such as cutting bulk carbon materials or solution synthesis. However, the on-surface synthesis has proven to be effective.Recently we successfully synthesized nitrogen-doped nanographene with an [18] annulene pore and its dimer through sequential reactions of debromination, aryl–aryl coupling, cyclodehydrogenation and C–N coupling on Ag(111).3) the Additionally, we fabricated multiple Cu atom-bridged nanographenes on Cu(111) by sequentially opening precursor molecules and forming coordination bonds.4) Moreover, we have synthesized π-extended N=7 armchair GNRs with nonplanar zigzag termini, which exhibits the Kondo effect on Au(111) surface.5)Furthermore, we have introduced silicon elements into the field of on-surface chemistry. Silabenzene, having unique heterocyclic rings with C-Si bonds, is still studied as a challenging target for the organosilicon chemistry due to their high reactivities. As an initial work, we synthesized two-dimensional covalent organic frameworks (COFs) (shown in Fig. 2) and graphene nanoribbons (GNRs) with disilabenzene linkers by reacting silicon atoms and precursor molecules on Au(111) surface.6) Next, we successfully synthesized C4Si rings incorporated nanographene and C6Si2 ring-bridged nanoribbon structures.7) We aim to extend on-surface chemistry of heavier group IVA elements.Research Digest 23Scanning Tunneling Microscopy for On-Surface Chemistry