Aza-triangulene: On-surface synthesis and electronic and magnetic properties

Abstract

Nitrogen heteroatom doping into a triangulene molecule allows tuning its magnetic state. However, the synthesis of the nitrogen-doped triangulene (aza-triangulene) has been challenging. Herein, we report the successful synthesis of aza-triangulene on the Au(111) and Ag(111) surfaces, along with their characterizations by scanning tunneling microscopy and spectroscopy in combination with density functional theory (DFT) calculations. Aza-triangulenes were obtained by reducing ketone-substituted precursors. Exposure to atomic hydrogen followed by thermal annealing and, when necessary, manipulations with the scanning probe afforded the target product. We demonstrate that on Au(111), aza-triangulene donates an electron to the substrate and exhibits an open-shell triplet ground state. This is derived from the different Kondo resonances of the final aza-triangulene product and a series of intermediates on Au(111). Experimentally mapped molecular orbitals match with DFT-calculated counterparts for a positively charged aza-triangulene. In contrast, aza-triangulene on Ag(111) receives an extra electron from the substrate and displays a closed-shell character. Our study reveals the electronic properties of aza-triangulene on different metal surfaces and offers an approach for the fabrication of new hydrocarbon structures, including reactive open-shell molecules. ; We acknowledge financial support from MCIN/AEI/10.13039/501100011033 (grant nos. PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-109555GB-I00, and FJC2019-041202-I); the Basque Government (IT-1255-19 and PIBA19-0004); the Spanish Research Council (ILINKC20002), the European Union's Horizon 2020 research and innovation program (grant no. 863098 and Marie Skłodowska-Curie Actions Individual Fellowship no. 101022150); and the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, grant no. ED431G2019/03). ; Peer reviewed