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

Abstract

Azobenzenei saprototypical molecular switch that can be reversibly photoisomerized between the nearly planar and apolar trans form, and the distorted, polar cis form. Most studies related to azobenzene derivatives have focused on planar adsorbed molecules.W ep resent herein the study of at hree-dimensional shape-persistent molecular architecture consisting of four tetrahedrally arranged azobenzene units that is adsorbed on aAg(111) surface.While the azobenzenes of the tripod in contact with the surface lost their switching ability, different isomers of the upright standing arm of the tetramer were obtained reversibly and efficiently by illumination at different wavelengths,r evealing time constants of only af ew minutes.D iffusion on the surface was dependent on the isomeric state-trans or cis-of the upright oriented azobenzenegroup.Hence,molecular mobility can be modulated by its isomeric state,which suggests that molecular growth processes could be controlled by external stimuli.

Azo bond formation on metal surfaces

“…[12,13] Among these N-based functional groups, the azo group shows valuable properties in photo switching. [14][15][16] In solution phase chemistry, azo compounds are obtained through an azo coupling using diazonium salts, but the cross-coupling of nitro and amino compounds remains challenging. Herein, onsurface azo formation by nitroarene-arylamine redox crosscoupling (path 1 in Scheme 1a) is successfully realized on the Ag(111) surface under ultrahigh vacuum (UHV) conditions.…”

Stacks of Azobenzene Stars: Self-Assembly Scenario and Stabilising Forces Quantified in Computer Modelling

“…There are several classifications of star-shaped azos: they may differ in (i) the number of arms (three [9,10,14,15,16,17,18,19,20], four [7,21,22], six [23,24,25], nine [26]), (ii) in their centres (nitrogen [9,19], phosphorus [27], silicon [28] or carbon atoms [21,22], benzene [14,16,20,29,30,31,32], polycyclic aromatic hydrocarbons [25,33], heterocyclic hydrocarbons [34,35,36,37], some chiral groups [6] or bio-active residues [38]), (iii) in the way azobenzenes are attached to the centre (covalently or noncovalently [39]), (iv) in their conformational rigidity (flexible or rigid), and (v) in their overall geometry (quasi-planar or 3D). Both the conformational rigidity and the shape of the star are closely related to the chemical nature of the star core.…”

A Scanning Tunneling Microscopy Study of the Photoisomerization of Diazocine

“…As a result, azobenzenes are attractive candidates for various photoresponsive molecular designs: optical data storage, , switchable sensors, , molecular machines, − vision restoration, − and artificial muscles . Surface–probe techniques such as scanning tunneling microscopy (STM) have been used extensively to study the isomerization of azobenzenes on metal surfaces stimulated by light − or inelastically tunneling electrons. − However, an understanding of how the local chemical environment of surface-bound molecules, i.e., arrangement of neighboring molecules and solvent presence, influences the nature of photoisomerization is scarce.…”