Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects

Abstract

On-surface synthesis has paved the way toward the fabrication and characterization of conjugated carbon-based molecular materials that exhibit π-magnetism such as triangulenes. Azatriangulene, a nitrogen-substituted derivative, was recently shown to display rich on-surface chemistry, offering an ideal platform to investigate structure−property relations regarding spin-selective charge transfer and magnetic fingerprints. Herein, we study electronic changes upon fusion of single molecules into larger dimeric derivatives. We show that the closed-shell structure of aza-triangulene on Ag(111) leads to closed-shell dimers covalently coupled through sterically accessible carbon atoms. Meanwhile, its open-shell structure on Au(111) leads to coupling via atoms displaying a high spin density, resulting in symmetric or asymmetric products. Interestingly, whereas all dimers on Au(111) exhibit similar charge transfer properties, only asymmetric ones show magnetic fingerprints due to spin-selective charge transfer. These results expose clear relationships among molecular symmetry, charge transfer, and spin states of π-conjugated carbon-based nanostructures.

N-Heterocyclic Carbene-Derived 1,3,5-Trimethylenebenzene: On-Surface Synthesis and Electronic Structure

“…For realizing their applications, the synthesis of di- and polyradicals as well as the understanding and control of their spin–spin coupling are important prerequisites. Over the past few decades, a number of diradicals have been reported, and the spin–spin coupling within diradicals (ferromagnetic or antiferromagnetic) and its correlation with the chemical structure have been explored. − For example, it has been shown that stable diradicals with strong ferromagnetic coupling can be prepared by incorporating two stable organic radicals, such as Blatter radical and nitronyl nitroxide radical, using a m -phenylene bridge unit. The spin coupling strength can be modulated through substitution, π-conjugation extension, and heteroatom doping . Compared with diradicals, the synthesis of triradicals is more challenging, and the spin–exchange interactions are more complicated because of the increased unpaired electrons, especially for triradicals with 3-fold symmetry .…”