Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
Langmuir. 2013 Sep 17;29(37):11623-31. doi: 10.1021/la402144g. Epub 2013 Sep 5.
Surface-bound azobenzenes exhibit reversible photoswitching via trans-cis photoisomerization and have been proposed for a variety of applications such as photowritable optical media, liquid crystal displays, molecular electronics, and smart wetting surfaces. We report a novel synthetic route using simple protection chemistry to form azobenzene-functionalized SAMs on gold and present a mechanistic study of the molecular order, orientation, and conformation in these self-assembled monolayers (SAMs). We use vibrational sum-frequency generation (VSFG) to characterize their vibrational modes, molecular orientation, and photoisomerization kinetics. Trans-cis conformational change of azobenzene leads to the change in the orientation of the nitrile marker group detected by VSFG. Mixed SAMs of azobenzene and alkane thiols are used to investigate the steric hindrance effects. While 100% azobenzene SAMs do not exhibit photoisomerization due to tight packing, we observe reversible switching (>10 cycles) in mixed SAMs with only 34% and 50% of alkane thiol spacers.
表面结合的偶氮苯通过反式-顺式光异构化表现出可逆光致变色，已被提议用于各种应用，如光可写光介质、液晶显示器、分子电子学和智能润湿表面。我们报告了一种使用简单保护化学的新合成途径，在金上形成偶氮苯功能化的自组装单层，并对这些自组装单层中的分子有序性、取向和构象进行了机理研究。我们使用振动和频产生（VSFG）来表征它们的振动模式、分子取向和光致异构化动力学。偶氮苯的反式-顺式构象变化导致 VSFG 检测到的腈标记基团的取向发生变化。偶氮苯和烷硫醇的混合自组装单层用于研究空间位阻效应。虽然由于紧密堆积，100%偶氮苯自组装单层不表现出光致异构化，但我们在仅含有 34%和 50%烷硫醇间隔物的混合自组装单层中观察到可逆切换（>10 个循环）。
