Exploiting Structural Flexibility for Reversible Kondo-State Switching in a Pure Organic Radical on Au(111)─Submolecular Imaging and Manipulation

Pure organic radicals are promising building blocks for spintronic and quantum computing devices. However, their practical implementation critically depends on the ability to control spin states on surfaces, which remains a fundamental challenge. Here, by combining submolecular characterizations via scanning tunneling microscopy/spectroscopy and noncontact atomic force microscopy with density functional theory calculations, we resolve two distinct adsorption conformations (3A and 3B) of a stable pure organic Blatter-type triradical (BTR) on Au(111) and identify their geometry-dependent Kondo states. Crucially, harnessing the structural flexibility of the BTR, we achieve reversible in situ switching between these Kondo states via tip manipulation. Furthermore, we demonstrate reversible spin-state toggling between spin-on radical states (3A and 3B) and spin-off hydrogenated states (3HA and 3HB) through controlled hydrogenation/dehydrogenation. Our work provides direct evidence of an intricate adsorption geometry-spin relationship in structurally flexible pure organic radicals, establishing structural flexibility as a design principle for molecular spintronic devices.