Stable π-radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) adsorbed at the elbows of $22\times \sqrt{3}$ reconstructed Au(111)

Highlights

• We provide single-molecule data of archetypal pi-radical DPPH on Au(111).

• We report energies and orbital maps of frontier orbital-related electronic states.

• Kondo-like state changes between peak and dip depending on tip position.

Abstract

Stable organic radicals serve as model systems for investigating metal-free magnetic phenomena at (sub)nanometer length scales. We have investigated at the single-molecule level the stable π-radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) adsorbed at the elbow sites of the $22\times \sqrt{3}$ reconstructed Au(111) surface. Low-temperature scanning tunneling microscopy (STM) and -spectroscopy under ultrahigh vacuum conditions at 8 K reveal structural as well as frontier-orbital related electronic details of DPPH/Au(111). A Kondo-like spectroscopic signature indicates preservation of the unpaired electron spin state.