Neutral Organic Radical Formation by Chemisorption on Metal Surfaces.

Organic radical monolayers (r-MLs) bonded to metal surfaces are potential materials for the development of molecular (spin)electronics. Typically, stable radicals bearing surface anchoring groups are used for generating r-MLs. Following a recent theoretical proposal based on a model system, we report the first experimental realization of a metal surface induced r-ML where a rationally chosen closed-shell precursor 3,5-dichloro-[bis-(2,4,6-trichlorophenyl)methylen]cyclohexa-2,5-diene-1-one (1) transforms into a stable neutral open-shell species (1*) via chemisorption on Ag(111) surface. X-ray photoelectron spectroscopy reveals that the >C=O group of 1 reacts with the surface forming a C-O-Ag linkage which induces an electronic rearrangement that transforms 1 to 1*. Importantly, Au is inert towards 1, while Cu surface leads to dehalogenation reactions. The radical nature of the monolayer was further confirmed by angle-resolved photoelectron spectroscopy and electronic structure calculations which provide evidence for the emergence of the singly occupied molecular orbital (SOMO) of 1*.