Stimuli-responsive luminescent liquid crystals: Change of photoluminescent colors triggered by a shear-induced phase transition
Stimuli-responsive luminescent liquid crystals: Change of photoluminescent colors triggered by a shear-induced phase transition
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DOI：
10.1002/anie.200800164
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Kato, Takashi
中科院分区：
文献类型：
--
作者：
Sagara, Yoshimitsu;Kato, Takashi
由分子自组装形成的软材料近年来备受关注。[1]液晶就是一种结合了有序状态和动态状态的软材料。 [2]这些特性可用于制造刺激响应材料。将光[3]电[4]和离子功能[5]部分掺入液晶中可产生动态功能材料，其功能可以通过刺激诱导的结构变化来调节。我们的目标是开发一类能够响应机械刺激的新型光功能纳米结构液晶，在此我们报告了芘衍生物 1 的剪切诱导液晶 (LC) 相变，它会引起光致发光颜色的变化。迄今为止，据报道，只有有限数量的液晶材料表现出剪切诱导相变，[6]并且据我们所知，尚未制备出表现出与光致发光颜色变化相关的剪切诱导液晶相变的光功能液晶。芘因其高荧光效率和准分子形成而成为一种广泛使用的探针，[7]并且最近报道了许多芘衍生物表现出LC行为。[8]我们打算利用芘基液晶的液晶有序相变来控制有序块体材料的发光性能。如果通过相变改变发光基团的组装结构，则可以通过外部刺激来调节材料的光致发光性能。[9]我们预计化合物1应同时表现出柱状和立方相，尽管合理设计诱导立方相并不容易。[2d]这些纳米结构液晶适合荧光团的排列。在化合物 1 中，两个树枝状基团通过酰胺键连接到中心芘部分。多种树枝状基团已被检测为液晶分子成分，[10-15]并且在焦点处具有甲基的树枝状基团与引入到1中的树枝状基团具有相似的结构，据报道显示出柱状相。[12]我们之前曾报道过具有大取代基的树枝状氢键分子表现出柱状-立方相变。 [16] 1 的有序相中氢键的存在预计会导致一维链结构的形成。 [17]化合物 1 由 1, 6-二乙炔基芘和扇形树枝通过 Sonogashira 偶联合成，产生透明、橙色粘稠液体，呈现黄色光致发光。化合物 1 显示热致液晶立方相，在简单加热下，其光学各向同性从 358C 到 1758C（图 1a）。 1 在 1608C 时的 X 射线衍射图（图 2a）显示 53.8、48.0、44.1 和 31.1 处的峰，d 间距倒数为 2：
Soft materials formed by molecular self-assembly have attracted much attention recently.[1] Liquid crystals are one such soft material that combines ordered and dynamic states.[2] These properties can be used to manufacture stimuli-responsive materials. The incorporation of photo-,[3] electro-,[4] and ion-functional [5] moieties into liquid crystals leads to dynamic functional materials, the functions of which can be tuned by stimuli-induced structural changes. We are aiming to develop a new class of photo-functional nanostructured liquid crystals that respond to mechanical stimuli, and herein we report on a shear-induced liquid-crystalline (LC) phase transition of pyrene derivative 1 which induces a change of photoluminescent color. To date, only a limited number of LC materials have been reported to show shearinduced phase transitions,[6] and to the best of our knowledge no photo-functional liquid crystals that show a shear-induced LC phase transition associated with a change of their photoluminescent color have been prepared. Pyrene is a widely used probe due to its high fluorescent efficiency and excimer formation,[7] and a number of pyrene derivatives have recently been reported to show LC behavior.[8] We intend to use the LC order-order phase transitions of pyrene-based liquid crystals to control the luminescent properties of the ordered bulk materials. If the assembled structures of luminescent groups are changed by the phase transition, the photoluminescent properties of the materials could be tuned by external stimuli.[9]We expected that compound 1 should exhibit both columnar and cubic phases, although it is not easy to design for the induction of a cubic phase rationally.[2d] These nanostructured liquid crystals are suitable for the arrangement of fluorophores. In compound 1, two dendritic groups are linked to a central pyrene moiety by amide bonds. A variety of dendritic groups have been examined as LC molecular components,[10–15] and the dendron having a methyl group at the focal point, which has a similar structure to that of the dendron introduced into 1, has been reported to show a columnar phase.[12] We have reported previously that dendritic H-bonded molecules with bulky substituents exhibit columnar–cubic phase transitions.[16] The presence of hydrogen bonding in the ordered phases of 1 is expected to lead to formation of a one-dimensional chain structure.[17] Compound 1 was synthesized from 1, 6-diethynylpyrene and the fan-shaped dendron by a Sonogashira coupling, which yielded a, transparent, orange viscous liquid that exhibits yellow photoluminescence. Compound 1 shows a thermotropic LC cubic phase that is optically isotropic from À358C to 1758C on simple heating (Figure 1 a). The X-ray diffraction pattern of 1 at 1608C (Figure 2a) shows peaks at 53.8, 48.0, 44.1, and 31.1 with a reciprocal d-spacing ratio of 2: