Conformational Molecular Switch of the Azobenzene Molecule: A Scanning Tunneling Microscopy Study

Abstract

We propose to utilize azobenzene as a nanomolecular switch which can be triggered by transmitting electrons above threshold biases. The effect is explained by an electron impact trans-cis conformational change of the isolated azobenzene molecules. The molecular electronic states of both isomers have been measured with spatially resolved scanning tunneling microscopy or spectroscopy, leading to suggested transition pathways of the electron-induced isomerization.

Reversible Photoswitching and Isomer‐Dependent Diffusion of Single Azobenzene Tetramers on a Metal Surface

“…The adsorption of azobenzene derivatives on a surface is advantageous since it confines the molecules to two dimensions and allows imaging of single molecules in real space by scanning probe microscopy 9, 10, 11, 12. The surface can have a strong influence on the isomerization process, that is, on the switching behavior,13 and subtle variations in the molecular interaction with the surface can be used to control molecular properties 14.…”

“…The other three arms (see Figure S5), which are adsorbed at the surface, are most likely always in the trans state 21, 27. This assignment is on one hand based on previous studies, in which the trans state of azobenzene derivatives is the energetically most stable form in the gas phase,1 in the solid state,8 and on various metal surfaces9, 10, 14, 27 after deposition at room temperature. Importantly, also tri‐azobenzene systems adsorb on Ag(111) with all azobenzene arms in the trans state,21 a configuration that is probably similar to the azo‐tripod linker in the present case.…”

Spatial periodicity in molecular switching

“…Switches represent a prototype of such functional molecules because they exhibit characteristic states of different physical/chemical properties, which can be addressed reversibly 3 . Recently, various switching entities have been studied and switching of single molecules on surfaces has been demonstrated [4][5][6][7][8][9][10][11][12][13] . However, for functional molecules to be used in a future device, it will be necessary to selectively address individual molecules, preferentially in an ordered pattern.…”

“…Molecular switches located on surfaces have been investigated extensively over recent years, particularly isolated molecules 4,5,12 and two-dimensional (2D) molecular aggregates [6][7][8][9][10][11]13 . These studies have mostly focused on azobenzene derivatives undergoing characteristic trans-cis isomerization triggered by light 7,8 , tunnelling electrons 4,5,13 or an electric field 6 .…”

“…These studies have mostly focused on azobenzene derivatives undergoing characteristic trans-cis isomerization triggered by light 7,8 , tunnelling electrons 4,5,13 or an electric field 6 . In some cases, multiple switching events seem to be influenced by adjacent molecules 9,10 .…”