Neutral Organic Radical Formation by Chemisorption on Metal Surfaces.

Abstract

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 to generate 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-4-[bis(2,4,6-trichlorophenyl)methylen]cyclohexa-2,5-dien-1-one (1) transforms into a stable neutral open-shell species (1•) via chemisorption onthe 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 that induces an electronic rearrangement that transforms 1 to 1•.We further show that surface reactivity is an important factor in this process wherebyAu(111) is inert towards1, whereas the Cu(111) surface leads to dehalogenation reactions. The radical nature of the Ag(111)-boundmonolayer was further confirmed by angle-resolved photoelectron spectroscopy and electronic structure calculations, which provide evidence of the emergence of the singly occupied molecular orbital (SOMO) of 1•.