Surface-Supported Hydrocarbon π Radicals Show Kondo Behavior

[Image: see text] Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7–50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support.