Li Chongqing, Ren Biye, Zhang Yi, Cheng Zhiyu, Liu Xinxing, Tong Zhen
Research Institute of Materials Science, South China University of Technology, Guangzhou, China.
Langmuir. 2008 Nov 18;24(22):12911-8. doi: 10.1021/la802101g. Epub 2008 Oct 18.
A novel ferroceneylazobenzene self-assembled monolayer (SAM) has been constructed on an indium-tin oxide (ITO) electrode via the covalent attachment of 4-(4'-11-ferrocenyl-undecanoxyphenylazo)benzoic acid ( FcAzCOOH) onto a silanized ITO substrate surface and verified by reflectance infrared spectroscopy and water contact angle. Atomic force microscopy (AFM) and cyclic voltammogram (CV) indicated that the FcAzCOOH formed a uniform and reproducible SAM on the ITO electrode with a surface coverage of ca. 1.9 x 10 (-10) mol/cm (2) (87 A (2)/molecule). The reversible photoisomerization behavior of the SAM was characterized by UV-vis spectra. The azo pi-pi* transition band intensity of the SAM gradually decreased with UV (365 nm) irradiation and was almost recovered again when subsequent exposure to ambient room light (400-800 nm). The increased tilt angle of the molecules on the ITO substrate after UV irradiation further confirmed the trans-to- cis isomerization of azobenzene moieties. The CV of the trans- FcAzCOOH modified ITO electrode showed a pair of waves due to redox of the ferrocene groups in the potential range of 0 to +800 mV (vs SCE), and the peak separation of the redox wave became larger after UV irradiation and almost returned to its original value after subsequent exposure to the visible light. Rate-dependent CV curves indicated that the charge transfer rate between the ferrocene species in the SAM and the ITO electrode was slowed down after UV irradiation due to the smaller porosity of the monolayer film and the more compact barrier layer between the redox species and the ITO electrode. It is the first time to directly observe the influence of photoisomerization of the azobenzene moiety on the redox behavior of redox species in the ferroceneylazobenzene-functionalized SAM. The present results provide profound insight into the role of redox microenvironment on electron transfer kinetics and also provide a simple and facile approach to the preparation of photocontrollable electrodes.
通过将4-(4'-11-二茂铁基-十一烷氧基苯基偶氮)苯甲酸(FcAzCOOH)共价连接到硅烷化的氧化铟锡(ITO)衬底表面，在ITO电极上构建了一种新型的二茂铁基偶氮苯自组装单分子层(SAM)，并通过反射红外光谱和水接触角进行了验证。原子力显微镜(AFM)和循环伏安图(CV)表明，FcAzCOOH在ITO电极上形成了均匀且可重复的SAM，表面覆盖率约为1.9×10(-10)mol/cm(2)(87 Å(2)/分子)。通过紫外可见光谱对SAM的可逆光异构化行为进行了表征。SAM的偶氮π-π*跃迁带强度随着紫外光(365 nm)照射逐渐降低，随后暴露于室内环境光(400 - 800 nm)时几乎又恢复。紫外照射后ITO衬底上分子倾斜角的增加进一步证实了偶氮苯部分的反式到顺式异构化。反式FcAzCOOH修饰的ITO电极的CV在0至+800 mV(相对于SCE)的电位范围内显示出由于二茂铁基团的氧化还原而产生的一对波，紫外照射后氧化还原波的峰间距变大，随后暴露于可见光后几乎恢复到其原始值。速率依赖性CV曲线表明，由于单分子层膜的孔隙率较小以及氧化还原物种与ITO电极之间的阻挡层更致密，紫外照射后SAM中二茂铁物种与ITO电极之间 的电荷转移速率减慢。这是首次直接观察到偶氮苯部分的光异构化对二茂铁基偶氮苯功能化SAM中氧化还原物种氧化还原行为的影响。目前的结果为氧化还原微环境在电子转移动力学中的作用提供了深刻的见解，也为制备光控电极提供了一种简单易行的方法。
