Tuning the Spin Interaction in Non-planar Organic Diradicals Through Mechanical Manipulation

• DOI: 10.48550/arxiv.2402.08641
• Publication Date: 2024-02-13
• Authors: Alessio Vegliante; Saleta Fernández; Ricardo Ortiz; Manuel Vilas‐Varela; Thomas Baum; Niklas Friedrich; Francisco Romero ...; Andrea Aguirre; Katerina Vaxevani; Dongfei Wang; Carlos García; Herre S. J. van d...; Thomas Frederiksen; Diego Peña; José Ignacio Pascual
• Keywords: Chemical Physics (physics.chem-ph); Carbon magnetism; Condensed Matter - Mesoscale and Nanoscale Physics; n-surface synthesis; Physics - Chemical Physics; Organic diradicals; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); FOS: Physical sciences; Scanning tunneling microscopy; Exchange coupling

Open-shell polycyclic aromatic hydrocarbons (PAHs) represent promising building blocks for carbon-based functional magnetic materials. Their properties stem from the presence of unpaired electrons localized in radical states $\pi$ character. Consequently, these materials are inclined to exhibit spin delocalization, form extended collective states, and respond flexibility molecular backbones. However, they also highly reactive, requiring structural strategies protect reacting with environment. Here, we demonstrate that open-shell ground state diradical 2-OS survives on a Au(111) substrate as global singlet formed by two anti-parallel spins coupled through conformational dependent interaction. The molecule is protected derivative Chichibabin's diradical, featuring non-planar geometry destabilizes closed-shell quinoidal structure. Using scanning tunneling microscopy (STM), interacting at edges, detected an excited triplet few millielectronvolts above state. Mean-field Hubbard simulations reveal exchange coupling between strongly depends torsional angles different moieties, suggesting possibility influencing molecule's changes. This was demonstrated here using STM tip manipulate conformation, while simultaneously detecting changes excitation spectrum. Our work suggests potential PAHs new class all-carbon spin-crossover