Real-Space Imaging of a Single-Molecule Monoradical Reaction

Abstract

Organic radicals consisting of light elements exhibit a low spin–orbit coupling and weak hyperfine interactions with a long spin coherence length, which are crucial for future applications in molecular spintronics. However, the synthesis and characterization of these organic radicals have been a formidable challenge due to their chemical instability arising from unpaired electrons. Here, we report a direct imaging of the surface chemical transformation of an organic monoradical synthesized via the monodehydrogenation of a chemically designed precursor. Bond-resolved scanning tunneling microscopy unambiguously resolves various products formed through a complex structural dissociation and rearrangement of organic monoradicals. Density functional theory calculations reveal detailed reaction pathways from the monoradical to different cyclized products. Our study provides unprecedented insights into complex surface reaction mechanisms of organic radical reactions at the single molecule level, which may guide the design of stable organic radicals for future quantum technology applications.

On-Surface Synthesis and Characterization of [7]Triangulene Quantum Ring

“…Isolated triangular-shaped molecules constitute approximately 26% of all the products, as estimated by a statistical analysis of multiple STM images. In addition, a magnified STM image of triangular-shaped products with a metallic tip resolves a dim hole-like feature in the molecular center (Figure b and Figure S1) and characteristic edge-localized nodal patterns, resembling the patterns observed at the zigzag edges of the zigzag-edged graphene nanostructures in the previous reports. ,,, To probe the chemical structure of an isolated product, we performed bond-resolved STM (BR-STM) imaging with a carbon monoxide-functionalized tip (CO-tip). − The BR-STM imaging was conducted at constant-height mode with reduced tip–sample distances (i.e., Pauli repulsion regime), wherein the CO molecule undergoes a lateral relaxation over the areas with high electron density (chemical bonds), which modulates the overall tunneling conductance between tip and sample, resulting in sharp features associated with the chemical bonds in the tunneling current image. , The corresponding BR-STM image of a single triangular-shaped molecule (Figure c) unambiguously resolves the molecular backbone consisting of 12 fused benzene rings with a clear-cut hexagonal antidot (a diameter of 5.7 Å) in the molecular center. Furthermore, the flat adsorption geometry of final products on Au(111) indicates the absence of any chemical bonding of molecule to the surface.…”

On-surface Synthesis of [7]triangulene Quantum Ring via Antidot Engineering

“…[13,14,29,30] To probe the chemical structure of an isolated product 1, we performed bondresolved STM (BR-STM) imaging with a carbon monoxide-functionalized tip (CO-tip). [31][32][33][34] The BR-STM imaging was conducted at constant-height mode with reduced tip-sample distances (i.e. Pauli repulsion regime), wherein the CO molecule undergoes a lateral relaxation over the areas with high electron density (repulsive) areas (chemical bonds), which modulates the overall tunneling conductance between tip and sample, resulting in sharp features associated with the chemical bonds in the current image.…”

Interactions between water and organic molecules or inorganic salts on surfaces

“…Nevertheless, there remain many open questions to be solved in the near future in terms of developing experimental techniques and theoretical models and further establishing methodologies in precise visualization and interpretation of detailed hydration processes for modeling the dynamics. In this sense, combination of various atomic-scale topographic characterization techniques (such as bond-resolved STM [14,62] and nc-AFM [63][64] ) and precise spectroscopic techniques with single-chemical-bond sensitivity (such as tipenhanced Raman spectroscopy [65][66] ) would give valuable and complementary indications involving both skeleton and chemical information in water-incorporated dynamic processes. Moreover, most of studies discussed here have been devoted to the well-defined solid surfaces under ultrahigh vacuum conditions as simplified model systems, while significant differences exist between the model systems and the ambient conditions of the real world.…”