Weizmann Institute of Science, Department of Materials and Interfaces, Rehovot Israel.
Beilstein J Nanotechnol. 2011;2:834-44. doi: 10.3762/bjnano.2.93. Epub 2011 Dec 20.
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.
基于分子的马达所固有的操纵和控制潜力具有巨大的科学和技术前景。在这方面，含偶氮苯基团的分子受到了广泛的研究。虽然已经通过多种技术宏观地检查了此类分子中偶氮基团的顺反异构化的影响，但自组装膜中弹性模量的变化尚未直接测量。在这里，我们使用原子力显微镜研究了在金岛的自组装膜中组织的双[（1,1'-联苯）-4-基]二氮烯在光开关时的机械响应。通过扭转谐波悬臂的高次谐波分析，可以实时提取机械数据。同时获得的弹性模量图谱和形貌图像的定量分析表明，顺式形式的模量大约是反式异构体的两倍。量子力学和分子动力学研究表明，这一实验结果与实验结果吻合良好，表明顺式形式的刚性响应既来自于单个分子键，也来自于膜中的分子间相互作用。这些结果展示了尖端原子力显微镜技术和先进计算方法的强大功能和见解。
