%0 Journal Article
%T Direct monitoring of opto-mechanical switching of self-assembled monolayer films containing the azobenzene group
%A Einat Tirosh
%A Enrico Benassi
%A Silvio Pipolo
%A Marcel Mayor
%J Beilstein Journal of Nanotechnology
%D 2011
%I 
%R 10.3762/bjnano.2.93
%X 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¨Ctrans 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.
%K AFM
%K azobenzene
%K elastic modulus
%K molecular dynamics
%K nanomechanics
%K photoswitch
%K quantum mechanics computation
%K self-assembled monolayer
%U http://dx.doi.org/10.3762/bjnano.2.93