Aza-Triangulene: On-Surface Synthesis, Electronic and Magnetic Properties

TL;DR

This study reports the successful on-surface synthesis of aza-triangulene, a nitrogen-doped triangulene, and investigates its electronic and magnetic properties on Au(111) and Ag(111) surfaces using microscopy, spectroscopy, and DFT calculations.

Contribution

It presents a new method for synthesizing aza-triangulene on metal surfaces and characterizes its electronic and magnetic states, revealing surface-dependent charge transfer and spin states.

Findings

Aza-triangulene exhibits an open-shell triplet ground state on Au(111).

On Ag(111), aza-triangulene receives an extra electron and shows a closed-shell character.

Experimentally observed molecular orbitals match DFT calculations for charged aza-triangulene.

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 perfectly 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 efficient approach for the fabrication of new hydrocarbon structures, including reactive open-shell molecules.