Surface-Isomerization Dynamics of trans-Stilbene Molecules Adsorbed on Si(100)-2×1

Abstract

Photoinduced trans-cis isomerization studies of stilbene molecules in the gas phase have led to a precise understanding of the corresponding molecular dynamics. Yet, when such molecules are adsorbed on surfaces, these reactions are expected to be strongly modified as compared to what is know in the gas phase. In this work, a low temperature (5 K) scanning tunneling microscope (STM) is used to image the trans-stilbene molecules deposited on a Si(100)-2 x 1 surface at 12 K. trans-Stilbene undergoes conformational changes during the adsorption process such that four different stilbene conformers are observed: trans-stilbene (TS), cis-stilbene (CS), and two new conformers I(1) and I(2). Furthermore, electronic excitation of individual stilbene molecules, by means of tunnel electrons, is shown to activate specific reversible molecular surface isomerization (TS <--> I(1) and CS <--> I(2)) combined with diffusion across the surface. Calculated STM topographies, using the tight binding method, indicate that the CS and TS molecules are physisorbed. The molecular conformations of the surface isomers I(1) and I(2) are suggested to be analogous to transient states conformations of the stilbene molecule when stabilized by the silicon surface. The measurements of the molecular surface isomerization and diffusion reaction yields are used to build a qualitative potential energy surface of the various stilbene reactions. The molecular surface-isomerization dynamics is shown to be influenced by the type of dopant (n or p). This is related to surface charging, which reveals modifications in the stilbene ionization potential.

Probing charge transfer dynamics in a single iron tetraphenylporphyrin dyad adsorbed on an insulating surface

“…x Texc) where e is the electron charge, Iexc. the tunnel current intensity during the excitation and Texc., the time needed to induce the conformation change 39,40,41 . This method is further explained in the Supplementary Fig.…”

“…The lateral movement of the acceptor along the surface is witnessed and correlated to the exchange of charge between monomers. Here, the robustness of a very well documented excitation process to control molecular manipulation 21,17,19,20,38,39,41,42 represents a corner stone to develop a complete novel approach to study charge transfer process at the nanoscale. Our investigations show that the transfer of holes is favored in the molecular dyad compared to the transfer of electrons.…”

Light driven reactions of single physisorbed azobenzenes

“…6 Recent studies demonstrated the switching of molecules adsorbed on Cu or even Si. 5,10 However, the chemisorption of the molecules alter the isomers such that the switch gets conformational rather than configurational.…”

Mechanism of a molecular photo-switch adsorbed on Si(100)

“…Nonetheless there are some reports on the adsorption and isomerization of molecules on silicon surfaces. 15,16 Zhang et al achieved switching within a surface that was completely covered by vertically oriented molecules, and the isomerization was controlled on the mm scale rather than on single molecules. In the study of Riedel et al the stilbene molecule switched between four adsorption configurations, a situation more complex and less desirable than a bistable isomerization process.…”