Study on structural phase transition induced by light in the organic dye crystal.

对光致变色材料的研究由来已久，但对其晶相的光致变色性还没有进行充分的分析。研究晶体相的光致变色具有很大的优势。当分子在晶体中规则排列时，我们可以知道原子在光致变色中的方向。在本研究中，我们处理质子转移的水杨酰亚胺(SA)。紫外光照射后，SA分子在烯醇相转变为酮相。也就是说，质子转移，苯环转动。酮相在b轴的吸收强度比c轴的强。相反，平行于c轴偏振的紫外光比平行于b轴偏振的紫外光更容易产生酮基相。这意味着光致变色的方向与酮相的电偶极跃迁方向不同。其次，我们测量了从烯醇到酮的转变以及从酮到酮的转变与温度的关系，得到了热激活能分别为24 meV和17 meV。这些值介于PMMA聚合物中SA分子的值和嵌在二苄基晶体中的SA分子的值之间。这些事实表明，与二苄基晶体中的SA相比，该分子更容易旋转，但与PMMA聚合物中的SA相比，它更难旋转。

Studies of photochromic materials have been made for a long time, but the photochromism in the crystal phase have not enough analyzed yet. Study of the photochromism in the crystal phase has a large advantage. As molecules array regularly in the crystal, we can know the direction of the atom in the photochromism. In the present study, we treat salicylideneanilines (SA) in which a proton transfers. The SA molecule in the enol phase changes to the keto phase after the ultraviolet light irradiation. Namely, the proton transfers and the benzen ring rotates. The absorption strength of the keto phase in the b-axis is stronger than that in the c-axis. On the contrary, the keto phase is generated more easily by ultraviolet light polarized parallel to the c-axis than by the light polarized parallel to the b-axis. This means that the direction of the photochromism is different from that of the electric dipole transition in the keto phase.Next, we measured temperature dependence of transformations from the enol to keto and vice versa, and obtained the thermal activation energies as 24meV and 17meV,respectively. These values are between those of the SA molecule in PMMA polymer and those of the SA molecule embedded in the dibenzyl crystal. These facts suggest taht the molecule rotates more easily compared to the SA in the dibenzyl crystal but it is difficult to rotate compared to the SA in the PMMA polymer.