Switching of an Azobenzene-Tripod Molecule on Ag(111)
Katharina Scheil, Thiruvancheril G. Gopakumar, Julia Bahrenburg, Friedrich Temps, Reinhard J. Maurer, Karsten Reuter, Richard Berndt, J. Phys. Chem. Lett. 7, 2080-2084 (2016)
We observe and interpret the mechanism of multistate switching of an Azobenzene Tripod on Ag(111) using STM, STS and Density Functional Theory.
The trans–cis isomerization makes azobenzene (AB) a robust molecular switch. Once adsorbed to a metal, however, the switching is inefficient or absent due to rapid excited-state quenching or loss of the trans–cis bistability. We find that tris- [4-(phenylazo)-phenyl]-amine is a rather efficient switch on Ag(111). Using scanning tunneling and atomic force microscopy at sub-molecular resolution along with density functional theory calculations we show that the switching process is no trans–cis isomerisation but rather a reorientation of the N–N bond of an AB unit. It proceeds through a twisting motion of the azo-bridge that leads to a lateral shift of a phenyl ring. Thus the role of the Ag substrate is ambivalent. While it suppresses the original bistability of the azobenzene units it creates a new one by inducing a barrier for the rotation of the N–N bond