Creation of Solid State Shearchromism by Shear Stress Effects

研究了剪切应力对光致变色螺吡喃类化合物的影响。我们使用了带有旋转机制的蓝宝石砧细胞，并在显微镜下用拉曼光谱测量进行了原位观察。这一结果将导致“剪切变色”和控制化学键的新方法的发展。剪切变形作用下，6-硝基螺吡喃薄膜的颜色由浅黄色变为绿色。对于绿色态，由于荧光较强，无法获得拉曼光谱。释放应力后，颜色由绿色变为紫色，荧光发射消失。紫色态的光谱为螺吡喃的光谱，有一些新的弱带叠加。这些条带表明一些螺吡喃分子转化为merocyanine。当静水压力大于剪应力1GPa时，观察到绿态的变色行为和强荧光。剪应力比压力使分子产生更有效的变形。6-硝基螺吡喃薄膜在常压下易由紫外光下的黄色变为紫色，在可见光下又变回黄色。但在紫外光照射下，剪应力下的绿色状态保持不变，在可见光照射下略有褪色。螺旋体在剪切变形下对光的响应较小。环糊精包合物6-硝基螺吡喃包合物在y-环糊精中表现出由剪切作用下的粉红色→暗红色→释放应力作用下的红紫色的变色行为。拉曼光谱结果表明，剪切应力诱导了merocyanine的转化，merocyanine分子在y-环糊精中稳定存在。此外，观察到比独立螺吡喃更快的光致变色行为。

The shear stress effects on the photochromic spiropyrans have been studied. We have used the sapphire anvil cell with the rotation mechanism and performed the in situ observations under a microscope with Raman spectroscopic measurements. The results should be led to the development of “shearchromism" and the new method for controlling chemical bonds.1. Shear stress effectsThe color of the thin film of 6-nitrospiropyran was remarkably changed from light-yellow to green under shear deformation. For the green state, the Raman spectrum could not be obtained because of the strong fluorescence. As being released stress, the color changed from green to purple and the fluorescent emission disappeared. The spectrum of the purple state was that of spiropyran with some new superimposed weak bands. These bands suggest that some spiropyran molecules are transformed to merocyanine. The chromic behavior to the green state and the strong fluorescence were observed also by the hydrostatic pressure over about 2.5GPa, which was larger than the estimated shear stress 1GPa. The shear stress gave more effective deformation to molecules than pressure.2. Photoresponsive propertiesThe thin film of 6-nitrospiropyran at ambient pressure was readily changed from yellow to purple with UV light and returned to yellow with visible light. However, the green state under shear stress remained after the irradiation of UV light and slightly faded with visible light. Spiropyrans under shear deformation less responded to the light.3. Cyclodextrin inclusion compoundThe inclusion compound of 6-nitrospiropyran in y-cyclodextrin has exhibited the chromic behavior from pink to dark red by shear stress and then to red-purple as releasing stress. Raman spectra showed that the transformation to merocyanine was induced under shear stress and that merocyanine molecule was stabilized in y-cyclodextrin. In addition, the more rapid photochromic behavior than independent spiropyran was observed.