On-surface synthesis of triangulene trimers via dehydration reaction

Abstract

Triangulene and its homologues are of considerable interest for molecular spintronics due to their high-spin ground states as well as the potential for constructing high spin frameworks. Realizing triangulene-based high-spin system on surface is challenging but of particular importance for understanding π-electron magnetism. Here, we report two approaches to generate triangulene trimers on Au(111) by using surface-assisted dehydration and alkyne trimerization, respectively. We find that the developed dehydration reaction shows much higher chemoselectivity thus resulting in significant promotion of product yield compared to that using alkyne trimerization approach, through cutting the side reaction path. Combined with spin-polarized density functional theory calculations, scanning tunneling spectroscopy measurements identify the septuple (S = 3) high-spin ground state and quantify the collective ferromagnetic interaction among three triangulene units. Our results demonstrate the approaches to fabricate high-quality triangulene-based high spin systems and understand their magnetic interactions, which are essential for realizing carbon-based spintronic devices.

Scanning probe microscopy in probing low-dimensional carbon-based nanostructures and nanomaterials

“…Consequently, the synthesis had long been elusive until the landmark work concerning the generation of [3] triangulene on surface via STM/AFM tip-induced dehydrogenation was reported by Pavlic ˇek et al [70] in 2017. The subsequent successful synthesis and characterization of [4]-, [5]-, and [7]-triangulenes [71][72][73] and [7]triangulene quantum ring [74] by SPM-based techniques have greatly expanded the fundamental understanding and further stimulated intensive exploration of triangulene family [69], such as triangulene dimer [75], trimer [76], chains [77], and aza-triangulene [78]. Moreover, by subtly combining solution synthesis and one-step on-surface cyclodehydrogenation, Hieulle et al reported the synthesis of a triangulene-based nanostar, which was a macrocycle constructed by six [3] triangulenes, and its spin excitations on Au(111) (figures 4(d)-(g)) [79].…”

Wide Tuning of Magnetic Exchange Coupling in Nanographenes through Orbital-Symmetry Engineering

“…As reported, antiferromagnetic coupling can be tuned to ferromagnetic coupling through adjusting the carbon-carbon bonding sites from the same or opposite sublattices. 12,33,40,41 The magnetic exchange interaction strength has also been tuned by including a connection spacer 42 or by incorporating π π a pentagon ring for tailoring singly occupied orbital overlap at the connecting region. 35 However, the effects of orbital symmetry on the magnetic exchange interaction have been rarely addressed.…”

“…1, should have an open-shell triplet ground state, which has been con rmed by a Kondo resonance showing a peak feature at the Fermi level in dI/dV spectra. 12,41 To visualize the spatial distribution of the spin excitation and the Kondo effect, dI/dV maps recorded at the excitation energies of 20 meV, 160 meV, and the Fermi energy are shown in Fig. 5c, respectively.…”

Organic Higher-Order Topological Insulators: Heterotriangulene-Based Covalent Organic Frameworks

“…Covalent organic frameworks (COFs) have emerged as a new class of polymers that enable the construction of ordered skeletons and polygonal pores and offer a chemistry platform allowing remarkable structural control and functional exploration. − The π-extended triangulene , and its hetero derivatives − have received widespread attention as molecular building units to form oligomers or polymer networks. Triangulene dimers/trimers linked by benzene rings as well as nanostar macrocycles formed by six triangulenes have been developed to study collective spin states. Recent experiments using substrate-mediated self-assembly have led to the formation of monolayer heterotriangulene-based COFs, − with a Dirac cone feature observed via angle-resolved photoelectron spectroscopy .…”

“…1−5 The π-extended triangulene 6,7 and its hetero derivatives 8−11 have received widespread attention as molecular building units to form oligomers or polymer networks. Triangulene dimers 12 /trimers 13 linked by benzene rings as well as nanostar macrocycles 14 formed by six triangulenes have been developed to study collective spin states. Recent experiments using substrate-mediated self-assembly have led to the formation of monolayer heterotriangulene-based COFs, 15−18 with a Dirac cone feature observed via angleresolved photoelectron spectroscopy.…”