Surface Relief Grating Formation Using Photochromic Amorphous Molecular Materials

近年来，利用两束相干激光照射偶氮苯功能化聚合物非晶薄膜形成表面浮雕光栅（SRG）受到了广泛的关注。SRG的形成是通过偶氮苯发色团的光致异构化引起的质量传递而发生的。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”的概念，并以偶氮苯和二噻吩乙烯为基础，合成了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类不需要聚合物粘结剂就能形成均匀非晶态薄膜的新型光致变色材料。它们具有的优点是，有没有光致变色的发色团相对于光致变色聚合物和复合聚合物系统，其中低分子量的光致变色化合物可以结晶在高concentration.In本研究中，我们设计和合成了几种新型的光致变色非晶分子材料，并阐明了它们的光致变色性能作为非晶薄膜以及在溶液中。此外，偶氮苯基光致变色非晶态分子材料的SRG形成也被研究，表明它们也构成了一类新的SRG形成材料。研究发现，随着玻璃化转变温度的升高，在光致变色非晶分子材料的非晶薄膜上形成的SRG的衍射效率和调制深度增加。光致变色无定形分子材料和具有相同侧基的相应的乙烯基聚合物之间的SRG形成的比较研究表明，SRG形成更迅速地为无定形分子材料比乙烯基聚合物。

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.