title: Direct monitoring of opto-mechanical switching of self-assembled monolayer films containing the azobenzene group.
abstract: The potential for manipulation and control inherent in molecule-based motors holds great scientific and technological promise. Molecules containing the azobenzene group have been heavily studied in this context. While the effects of the cis-trans isomerization of the azo group in such molecules have been examined macroscopically by a number of techniques, modulations of the elastic modulus upon isomerization in self-assembled films were not yet measured directly. Here, we examine the mechanical response upon optical switching of bis[(1,1'-biphenyl)-4-yl]diazene organized in a self-assembled film on Au islands, using atomic force microscopy. Analysis of higher harmonics by means of a torsional harmonic cantilever allowed real-time extraction of mechanical data. Quantitative analysis of elastic modulus maps obtained simultaneously with topographic images show that the modulus of the cis-form is approximately twice that of the trans-isomer. Quantum mechanical and molecular dynamics studies show good agreement with this experimental result, and indicate that the stiffer response in the cis-form comprises contributions both from the individual molecular bonds and from intermolecular interactions in the film. These results demonstrate the power and insights gained from cutting-edge AFM technologies, and advanced computational methods.
authors.affiliation: Weizmann Institute of Science, Department of Materials and Interfaces, Rehovot Israel.
authors.forename: Einat
authors.initials: E
authors.lastname: Tirosh
authors.forename: Enrico
authors.initials: E
authors.lastname: Benassi
authors.forename: Silvio
authors.initials: S
authors.lastname: Pipolo
authors.forename: Marcel
authors.initials: M
authors.lastname: Mayor
authors.forename: Michal
authors.initials: M
authors.lastname: Valášek
authors.forename: Veronica
authors.initials: V
authors.lastname: Frydman
authors.forename: Stefano
authors.initials: S
authors.lastname: Corni
authors.forename: Sidney R
authors.initials: SR
authors.lastname: Cohen