Colusso Aaron V, McDonagh Andrew M, Gentle Angus, Cortie Michael B
Institute for Nanoscale Technology, University of Technology Sydney PO Box 123, Broadway NSW 2007 Australia
RSC Adv. 2018 May 23;8(34):18776-18783. doi: 10.1039/c8ra03731k. eCollection 2018 May 22.
The photochromic properties of a hybrid compound comprised of the surfactant cation cetyltrimethylammonium [(CH)N(CH)] (CTA) and the isopolytungstate anion [HWO] is investigated. The compound, which has the nominal formula (CTA)[HWO]Cl·2HO, changes from white to blue when exposed to UV radiation. The sample returns to the bleached state if stored in the dark-ambient. Application of XPS indicates that the coloring species are W and W. The CTA component is found by XPS and FTIR to undergo progressive and irreversible oxidation during this cycle. Examination of FTIR suggests that the changes occur at multiple sites across the amphiphile. Surprisingly, the photochromic cycle is correlated with changes in the X-ray diffraction pattern, indicating partially reversible changes in the ordering of the Keggin ions and their spacing. In particular, application of the UV radiation causes the progressive accumulation of strain in the [001] direction. This is due to permanent oxidative changes in the CTA accumulating from cycle to cycle, resulting in an increase in interlamellar-distance due to less interdigitation of the chains. This provides a controllable photomechanical response.
对一种由表面活性剂阳离子十六烷基三甲基铵[（CH）N（CH）]（CTA）和同多钨酸根阴离子[HWO]组成的杂化化合物的光致变色特性进行了研究。该化合物的标称化学式为（CTA）[HWO]Cl·2HO，在紫外辐射下会从白色变为蓝色。如果储存在黑暗环境中，样品会恢复到漂白状态。X射线光电子能谱（XPS）分析表明，显色物种为W和W。通过XPS和傅里叶变换红外光谱（FTIR）发现，CTA组分在这个循环过程中会发生渐进且不可逆的氧化。FTIR分析表明，两亲分子的多个位点都发生了变化。令人惊讶的是，光致变色循环与X射线衍射图谱的变化相关，这表明Keggin离子的有序性及其间距发生了部分可逆变化。特别是，紫外辐射的作用会导致[001]方向上应变的逐渐积累。这是由于CTA中永久性氧化变化在循环中不断积累，导致链间相互穿插减少，层间距离增加。这提供了一种可控的光机械响应。
