Optically and thermally induced molecular switching processes at metal surfaces

Abstract

Using light to control the switching of functional properties of surface-bound species is an attractive strategy for the development of new technologies with possible applications in molecular electronics and functional surfaces and interfaces. Molecular switches are promising systems for such a route, since they possess the ability to undergo reversible changes between different molecular states and accordingly molecular properties by excitation with light or other external stimuli. In this review, recent experiments on photo- and thermally induced molecular switching processes at noble metal surfaces utilizing two-photon photoemission and surface vibrational spectroscopies are reported. The investigated molecular switches can either undergo a trans-cis isomerization or a ring opening-closure reaction. Two approaches concerning the connection of the switches to the surface are applied: physisorbed switches, i.e. molecules in direct contact with the substrate, and surface-decoupled switches incorporated in self-assembled monolayers. Elementary processes in molecular switches at surfaces, such as excitation mechanisms in photoisomerization and kinetic parameters for thermally driven reactions, which are essential for a microscopic understanding of molecular switching at surfaces, are presented. This in turn is needed for designing an appropriate adsorbate-substrate system with the desired switchable functionality controlled by external stimuli.

UV/Vis Spectroscopy Studies of the Photoisomerization Kinetics in Self-Assembled Azobenzene-Containing Adlayers

“…This is in contrast to azobenzene derivatives adsorbed planar on Au surfaces, where the photoswitching efficiency was found to be reduced by five orders of magnitude 51 . More precisely, the cross sections of the azobenzene-TATA SAMs are similar or even larger than those in the corresponding solutions (see Figure 9 and Table 2).…”

Controlling Motion at the Nanoscale: Rise of the Molecular Machines

“…161,162 Physically and electronically decoupling these functional moieties from surfaces or from neighboring molecules is often necessary to avoid steric constraints or quenching of excited states. [163][164][165][166][167][168] For example, molecular rotors can be tethered such that the axis of rotation is aligned parallel or perpendicular to the surface, in either altitudinal or azimuthal orientations, respectively. Feringa and coworkers reported the tunable and reversible wettability of gold surfaces modified with SAMs of altitudinal rotors based on light-driven overcrowded alkenes bearing perfluorinated alkyl chains (Figure 12a).…”

Diarylethene Molecules on a Ag(111) Surface: Stability and Electron-Induced Switching

“…1 Whereas many classes of molecular switches have been designed and successfully employed as functional entities in solution or in molecular crystals, 2,3 their functionality on metal surfaces is yet very limited. 4,5 The change in electronic properties upon adsorption is typically accompanied by a modification of potential energy landscapes 1 PDTE isomers adsorbed on the Ag(111) surface. From these simulations we determine the relative thermodynamic and kinetic stabilities of the isomers, as well as their electronic structure, that can be used to interpret the measured differential conductance spectra.…”