Stable π Radical BDPA: Adsorption on Cu(100) and Survival of Spin

The adsorption of the radical α,ɣ-bisdiphenylene-β-phenylallyl (BDPA) molecule to the Cu(100) surface was studied using scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), and density functional theory (DFT) calculations accounting for dispersion forces. BDPA on Cu(100) was observed to align preferentially along <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>⟨</mml:mo> <mml:mn>01</mml:mn> <mml:mover><mml:mn>1</mml:mn> <mml:mo>‾</mml:mo></mml:mover> <mml:mo>⟩</mml:mo></mml:mrow> <mml:annotation>${\langle 01\bar{1}\rangle }$</mml:annotation> </mml:semantics> </mml:math> directions due to weak Cu-C chemisorption between fluorenyl carbons with the underlying copper atoms. The curved shape of the BDPA molecule on Cu(100) can be ascribed to the lack of molecular orbital character on the phenyl substituent. A Kondo-like feature from differential conductance (dI/dV) measurements centered close to the Fermi energy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>E</mml:mi> <mml:mi>F</mml:mi></mml:msub> <mml:annotation>${{E}_{{\rm F}}}$</mml:annotation> </mml:semantics> </mml:math> ) suggests the retention of an electron spin-1/2 state, which is corroborated by hybrid DFT calculations that place the SOMO (singly occupied molecular orbital) below and SUMO (singly unoccupied molecular orbital) above <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>E</mml:mi> <mml:mi>F</mml:mi></mml:msub> <mml:annotation>${{E}_{{\rm F}}}$</mml:annotation> </mml:semantics> </mml:math> for BDPA adsorbed to Cu(100).