Photoinduced Surface Relief Grating Formation on a Co-crystal of 4-[Bis(9,9-dimethylfluoren-2-yl)amino]azobenzene and Ethyl Acetate
Photoinduced Surface Relief Grating Formation on a Co-crystal of 4-[Bis(9,9-dimethylfluoren-2-yl)amino]azobenzene and Ethyl Acetate
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DOI：
10.1002/cphc.200800419
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发表时间：
2008-10-24
期刊：
影响因子：
2.9
通讯作者：
Nakano, Hideyuki
中科院分区：
文献类型：
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作者：
Nakano, Hideyuki
近年来，光辐照引起的材料的机械运动，即所谓的“光机械效应”，引起了人们的极大关注。光致变色材料中观察到的光机械效应的几个例子，如液晶偶氮聚合物网络膜的弯曲[1]和二芳基乙烯衍生物分子晶体的可逆形状变化[2]已经报道。光致表面浮雕光栅（SRG）的形成观察偶氮苯为基础的材料，诱导的质量传输后，与相干激光束的干涉曝光的薄膜，也是一个重要的光机械效应。已经使用各种系统进行了许多研究，包括偶氮苯基无定形聚合物，[3-10]偶氮苯基液晶膜，[11-16]掺杂螺吡喃[17]和二芳基乙烯衍生物的聚（甲基丙烯酸甲酯）膜，[18]和能够光化学交联的聚合物液晶。[19我们已经研究了使用偶氮苯基光致变色非晶分子材料（即，自身形成非晶玻璃的低分子量光致变色分子）的光诱导SRG形成。[21-25]例如，调制深度为ca.在4-[双（9，9-二甲基芴-2-基）氨基]偶氮苯（BFlAB）的非晶薄膜上可以制备出500 nm的薄膜。[25]其他研究小组也报道了使用无定形分子材料的光诱导SRG形成。[26-29]关于使用偶氮苯基材料的光诱导SRG形成，据信通过偶氮苯发色团的反式-顺式和顺式-反式异构化诱导质量传递以产生SRG。光生SRG的形成很大程度上取决于写入光束的偏振方向。[8，21，25]已经提出了几种光诱导SRG形成机制的模型;[3-9，16，30]然而，细节尚不清楚。与已经描述的无定形和液晶材料相反，有机晶体上的光诱导SRG形成是本文感兴趣的主题。虽然偶氮苯衍生物的光致变色反应似乎被限制在大部分的晶体，靠近表面的分子有可能参加反应，从而诱导SRG的形成。最近，我们已经证明，光诱导的SRG形成可以发生在4-（二甲氨基）偶氮苯（DAAB）的单晶上[31]，并且我们发现写入光束的偏振对单晶上SRG形成的影响与所报道的无定形聚合物和光致变色无定形分子材料的影响完全不同。然而，在有机晶体上光诱导SRG的形成仍处于研究的早期阶段，细节尚未阐明。在此，新获得了BFlAB（方案1）和乙酸乙酯的共晶（BFlAB-AcOEt），并且首次观察到在共晶表面上发生光诱导SRG形成。此外，写入光束的偏振对SRG形成的影响不同于DAAB单晶。
Recently, mechanical motions of materials induced by photo irradiation, known as “photomechanical effects”, have attracted a great deal of attention. Several examples of photomechanical effects observed for photochromic materials, such as bending of liquid-crystalline azo-polymer network films [1] and reversible shape changes of molecular crystals of diarylethene derivatives,[2] have been reported. Photoinduced surface relief grating (SRG) formation observed for films of azobenzene-based materials, induced by mass transport upon interference exposure with coherent laser beams, is also an important photomechanical effect. A number of studies have been done using a variety of systems including azobenzene-based amorphous polymers,[3–10] azobenzene-based liquid crystalline films,[11–16] poly (methyl methacrylate) films doped with spiropyran [17] and diarylethene derivatives,[18] and polymer liquid crystals able to be cross-linked photochemically.[19, 20] We have studied photoinduced SRG formation using azobenzene-based photochromic amorphous molecular materials, namely, low molecular-weight photochromic molecules that form amorphous glasses by themselves.[21–25] For example, relatively large SRGs with a modulation depth of ca. 500 nm could be fabricated on an amorphous film of 4-[bis (9, 9-dimethylfluoren-2-yl) amino] azobenzene (BFlAB).[25] Photoinduced SRG formation using amorphous molecular materials have also been reported by other groups.[26–29] With regard to photoinduced SRG formation using azobenzene-based materials, it is believed that mass transport is induced by trans–cis and cis–trans isomerizations of the azobenzene chromophore to produce a SRG. Photoinduced SRG formation greatly depends on the polarization direction of the writing beams.[8, 21, 25] Several models for the mechanism of photoinduced SRG formation have been proposed;[3–9, 16, 30] however, the details are not known. In contrast to the amorphous and liquid crystalline materials already described, photoinduced SRG formation on organic crystals is the subject of interest herein. Although the photochromic reactions of azobenzene derivatives seem to be restricted within the bulk of the crystal, the molecules near the surface have the potential to take part in reactions and hence to induce SRG formation. Very recently, we have demonstrated that photoinduced SRG formation can take place on a single crystal of 4-(dimethylamino) azobenzene (DAAB)[31] and we found that the effect of the polarization of the writing beams on the SRG formation on a single crystal was quite different from that reported for amorphous polymers and photochromic amorphous molecular materials. However, photoinduced SRG formation on organic crystals is still at an early stage of investigation and details have not been elucidated yet. It is necessary to find a variety of organic crystals on which photoinduced SRG formation takes place.Herein, a co-crystal of BFlAB (Scheme 1) and ethyl acetate (BFlAB–AcOEt) was newly obtained and, for the first time, photoinduced SRG formation was observed to take place on the surface of a co-crystal. In addition, the effect of the polarization of the writing beams on SRG formation was different from that observed for the DAAB single crystal.