Ligand Driven, Light-Induced Spin-Crossover

自旋交叉化合物的合成及其固态化学和物理研究是当前国际上的一个热点。这些是在施加热、光或一些其他物理刺激时可以经历磁矩的可逆变化的材料。这通常对应于过渡金属中心的高自旋到低自旋d电子跃迁，因此伴随着颜色变化。像这样的材料，其颜色可以可逆地快速切换，在显示设备和光学计算等方面具有潜在的应用。我们研究2，6-二吡唑吡啶类化合物的铁化学已有一段时间。这些配体的铁（II）络合物通常在室温附近或在低温下的激光照射下经历自旋交叉转变。不寻常的是，我们可以通过适当取代我们的有机配体，相当可靠地控制它们的温度诱导颜色变化（热致变色）的温度。相反，我们最近发现，在我们的铁配合物中的吡啶环的取代对它们的自旋交叉行为的影响很小。这是一个有用的结果，使我们能够将其他基团附加到我们的铁中心，而不会损害它们的热致变色性，为我们提供了一条多功能分子器件的途径。我们现在希望将我们的系统应用于光驱动、光诱导的自旋交叉现象。也就是说，利用我们分子外围光敏基团的机械运动来驱动铁中心的自旋状态变化。这个想法以前已经在相当有限的模型系统中得到了证明。虽然到目前为止，通过这种途径实现的开关通常是不完全的，但它具有在室温下工作的优点。使用激光转换铁化合物的其他方法更有效，但通常只能在-130摄氏度以下工作。我们将制造新版本的铁（II）复合物，其中包含两种类型的光敏触发器。首先，是在UV光下围绕双键进行顺式/反式异构化的基团。第二，是在UV照射时经历可逆开环反应的基团。使用后者，我们希望产生一个光驱动的构象自旋交叉开关，作为（多）晶体固体，这是以前没有实现的。

The synthesis, and solid state chemistry and physics, of spin-crossover compounds is of great international interest at present. These are materials that can undergo a reversible change in magnetic moment upon application of heat, light or some other physical stimulus. This most commonly corresponds to a high-spin-to-low-spin d-electron transition at a transition metal centre, and so is accompanied by a colour change. Materials like these, whose colours can be reversibly and rapidly switched, have potential applications in display devices and in optical computing, among other things. We have been studying the iron chemistry of 2,6-dipyrazolylpyridines for some time. Iron(II) complex compounds of these ligands often undergo spin-crossover transitions near room temperature or under laser irradiation at low temperatures. Unusually, we can control the temperature of their temperature-induced colour change ( thermochromism ) fairly reliably, by appropriate substitution of our organic ligands. Conversely, we have recently found that substitution of the pyridine ring in our iron complexes has very little effect on their spin-crossover behaviour. That is a useful result that allows us to append other groups to our iron centres without compromising their thermochromism, giving us a route into multifunctional molecular devices. We now wish to apply our system to the phenomenon of light-driven, light-induced spin-crossover. That is, using mechanical motion at a light-sensitive group on the periphery of our molecules to drive a spin-state change at their iron centres. This idea has been demonstrated before, in a rather limited range of model systems. Although the switching achieved by this route up to now has generally been incomplete, it has the advantage of working at room temperature. Other ways of switching iron compounds using laser light are more efficient, but usually only work below -130 degrees Centigrade.We will make new versions of our iron(II) complexes containing two types of light-sensitive trigger. First, are groups that undergo cis/trans isomerisations about a double bond under UV light. Second, is a group that undergoes a reversible ring-opening reaction upon UV irradiation. Using the latter we hope to produce a light-driven conformational spin-crossover switch that works as a (poly)crystalline solid, which has not been achieved before.