Direct monitoring of opto-mechanical switching of self-assembled monolayer films containing the azobenzene group

作者：Tirosh Einat; Benassi Enrico; Pipolo Silvio; Mayor Marcel; Valasek Michal; Frydman Veronica; Corni Stefano^*; Cohen Sidney R

来源：Beilstein Journal of Nanotechnology, 2011, 2: 834-844.

DOI：10.3762/bjnano.2.93

• AFM
• azobenzene
• elastic modulus
• molecular dynamics
• nanomechanics
• photoswitch
• quantum mechanics computation
• self-assembled monolayer

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.

• 出版日期2011-12-20