Surface Relief Grating Formation Using Photochromic Amorphous Molecular Materials

近年来，用两束相干激光辐照偶氮苯功能化聚合物的非晶膜形成表面起伏光栅（SRG）受到了广泛的关注。SRG的形成是由偶氮苯发色团的光异构化引起的质量传递引起的。虽然已经提出了一些SRG形成的模型，但详细的机制尚未阐明。作为非晶态分子材料研究的一部分，我们提出了“光致变色非晶态分子材料”的新概念，并创建了以偶氮苯和二乙烯为基材的两类光致变色非晶态分子材料。光致变色非晶态分子材料是一种新型的光致变色材料，可以在不需要高分子结合剂的情况下自行形成均匀的非晶态薄膜。它们的优点是，相对于光致变色聚合物和复合聚合物体系，光致变色发色团不会被稀释，在这些体系中，低分子量的光致变色化合物可能在高浓度下结晶。在本研究中，我们设计并合成了几种新型的光致变色非晶态分子材料，并阐明了它们在非晶态薄膜和溶液中的光致变色性能。此外，利用偶氮苯基光致变色非晶分子材料制备SRG的研究表明，它们也构成了一类新的SRG形成材料。在光致变色非晶分子材料的非晶膜上形成的SRG的衍射效率和调制深度随着玻璃化转变温度的升高而增加。光致变色非晶态分子材料与相应的具有相同垂基团的乙烯基聚合物形成SRG的比较研究表明，非晶态分子材料比乙烯基聚合物形成SRG的速度更快。

Recently, formation of surface relief grating (SRG) by irradiation of amorphous films of azobenzene-functionalized polymers with two coherent laser beams has received a great deal of attention. SRG formation takes place by the mass transport induced by the photoisomerization of the azobenzene chromophore. Although a few models for SRG formation have been proposed, detailed mechanism has not yet been elucidated.As a part of our studies on amorphous molecular materials, we have proposed a new concept, "photochromic amorphous molecular materials" and have created two families of photochromic amorphous molecular materials based on azobenzene and dithienylethene. Photochromic amorphous molecular materials constitute a new class of photochromic materials that form uniform amorphous films by themselves without polymer binders. They have an advantage that there is no dilution of photochromic chromophores relative to photochromic polymers and composite polymer systems, where low molecular-weight photochromic compounds may crystallize at high concentrations.In the present study, we have designed and synthesized several novel photochromic amorphous molecular materials and elucidated their photochromic properties as amorphous films as well as in solution. In addition, SRG formation using azobenzene-based photochromic amorphous molecular materials has been investigated, showing that they also constitute a new class of SRG-forming materials. The diffraction efficiency and the modulation depth of SRG formed on amorphous films of photochromic amorphous molecular materials were found to increase with increasing the glass-transition temperatures. Comparative study of SRG formation between a photochromic amorphous molecular material and the corresponding vinyl polymer with the same pendant group showed that SRG is formed more rapidly for the amorphous molecular material than for the vinyl polymer.