我们感激地感谢赠款、ERC-2012-StG_20111012 FOLDHALO (307108 号赠款协议) 的支持。

注: 在氮气气氛下, 在烘干玻璃器皿中进行反应。请遵照每种化学品的 MSDS 中所描述的安全措施。
1. 1-烷基3咪唑碘盐的合成 (1 米,图 3)
<ol><li>在一个三颈, 圆底烧瓶装有回流冷凝器装有氮气入口, 温度计, 磁搅拌棒, 和加热油浴, 溶解1.5 克 (0.018 摩尔, 1 equiv) 新鲜蒸馏的1-甲基咪唑和1。3equiv 的 1-iodoalkane (链长度从 C2 到 C12) 在10毫升的乙腈。</li>
	<li>将反应混合物加热到回流 (75-80 °c 内部温度), 在氮气气氛下过夜, 然后将混合物冷却到室温。</li>
	<li>使用旋转蒸发器将所产生的混合物中的挥发性材料从减少的压力降低到50摄氏度。 注: 鎓盐具有高度的吸湿和快速吸收空气中的水分。因此, 建议将其存储在干燥中, 直到使用。</li>
</ol>2. 1-米· 2-n 的预算外综合体的合成
<ol><li>
过程 1: 从解决方案 (仅在图 1中的1-2 ·2-8 中)
	<ol>
<li>1-乙基3咪唑碘 (1-2, 兆瓦 = 238.07 克/摩尔) 的溶液, 通过溶解50毫克 (0.21 毫摩尔, 1 equiv) 1-2 在乙腈的0.5 毫升. </li>
		<li>perfluorooctyl 碘化物 (2-8, 兆瓦 = 545.96 克/摩尔) 的溶液, 通过溶解229毫克 (0.42 毫摩尔, 2 equiv) 的 2-8 在乙腈的0.5 毫升. </li>
		<li>把两个溶液混合在一个瓶子里, 把瓶子放在一个装满石蜡油的罐子里。</li>
		<li>使溶剂在室温下在石蜡油中慢慢扩散。经过3至7天的时间, 得到了适合 X 射线衍射分析的优质单晶。</li>
	</ol>
</li>
	<li>
程序 2: 熔体方法学 注意: 这种方法需要一个空气密封系统, 以减轻 iodoperfluoroalkanes 的波动性。<ol>
<li>将每个 1-烷基-3-咪唑碘 (1m) 与适当的 iodoperfluoroalkanes (2n) 混合在一个有磁性搅拌棒的透明硼硅酸盐玻璃瓶中, 在1:2 摩尔比率中。</li>
		<li>关闭瓶子, 并把它在激烈搅拌下的油浴。</li>
		<li>热量在70摄氏度使用热板15分钟, 然后冷却的混合物, 以室温。</li>
	</ol>
</li>
</ol>3. 1H 和19F 核磁共振实验
注: 1H nmr 和19F 核磁共振谱记录在25°c 上, 其工作于499.78 兆赫, 用于 1 H 和 470.21 mhz, 用于, 并使用 CDCl 19 作为溶剂。TMS 和 CFCl3被用作校准1H 核磁共振和19F 核磁共振的化学位移的内部标准。含有氢和氟核的双 (22、2-trifluoroethyl) 醚作为内部标准, 用于在 cocrystals 中建立1m 和2n 之间的比值。
<ol><li>
核磁共振分析和光谱标定样品的制备
	<ol>
<li>溶解约10毫克的每一个复杂的1米· 2-n 在0.5 毫升的 CDCl3。</li>
		<li>添加1µL 22, 2-trifluoroethyl 醚使用微。</li>
		<li>锁定该示例, 设置在表 1中报告的捕获参数, 并记录1H 和19F nmr 连续光谱, 而不从磁铁中删除核磁共振管, 以便在相同的操作条件下运行。</li>
		<li>校准集成参数, 以便在1H 核磁共振谱中的 CH2O 四重奏 (22, 2-trifluoroethyl) 醚 (δ = 4.3 ppm) 对应于四, 在19F NMR 谱中, CF3三重 (δ = −74.5 ppm) 的 22, 2-trifluoroethyl 醚对应于六。</li>
		<li>计算在19F 核磁共振谱中从2-n (δ = −61.2 ppm) 派生的 CF2I 信号区域的比率) 和从1m ( 1H 核磁共振谱中的δ≈ 4.0 ppm) 派生的 CH3信号区域, 为了计算每个复合体中2-n 和1m 之间的比率。</li>
	</ol>
</li>
</ol>4. 热级偏振光学显微镜 (POM) 样品的制备
<ol><li>在两个微盖玻璃 (18 毫米 x 18 毫米) 之间放置一个超分子复合体1-m• 2n 的铲头量, 以制备样品薄层。</li>
	<li>将样品放在两个交叉偏振片之间的热阶段, 并将样品加热熔化。</li>
	<li>将样品提交给反复加热/冷却循环, 以促进相变。晶体和液晶相会与偏振光相互作用, 导致亮度和颜色梯度, 而各向同性相则会出现暗色。</li>
</ol>

作者没有什么可透露的。

我们报告了一个简单和通用的协议, 以合成的预算外氟化签订, 其中 mesomorphicity 是由超分子阴离子 [CnF2 n + 1-I∙∙∙I∙∙∙InF2 n + 1]-。
根据 1-烷基-3-咪唑盐的离子液体可以表现出液态结晶行为, 这是公认的。然而, 无论阴离子, 没有 mesophases 被观察到的化合物与烷基链短于12碳原子。因此, 所报道的材料最引人注目的方面是, 它是外相阴离子的各向异性, 确定中间相形成。事实上, 严格的几何约束的预算外强加的分子间相互作用发生沿扩展的 c-I 键, 在西格玛孔, 与角度接近180°。碘化阴离子作为二齿的预算外受体, 结合两个氟模块, 显示线性排列围绕中央碘化阴离子。此外, 烷基链比等效 HC 链更硬, 并采用扭曲的螺旋结构, 由于13配置 CF2组9,52之间的排斥, 进一步促进了生成刚性, 棒状 superanions。
这完全同意的观察, 其中包含 iodoperfluorodecane (2-10) 显示的过渡温度高于那些包含 iodoperfluorooctane (2-8), 因为前者是更多的各向异性。此外, 已知趋势45、53 fluoroalkanes 打包成层状阶段决定了 SmB 和 SmA 阶段的获取。
本文报道的 superfluorinated 签订首次证明了在鎓盐的基础上签订的应用。多亏了一个精确的超分子设计的基础上的高方向性的预算外和 fluorophobic 效应, 有可能获得 enantiotropic 液晶基于刚性, 非芳香, 预算外超分子 synthon 作为液晶核心。液晶行为与烷基链的长度无关。
这里提出的超分子方法代表了一个有吸引力的平台, 设计新的液晶材料, 并可以为开发先进的功能材料, 如室温离子提供了新的机会导体, photoresponsive 签订, 液晶电解质, 用于能源设备中。

分子间相互作用在测定散装材料的理化性质方面起着非常重要的作用。当新的交互作用变为可用时, 新的结构 (即新函数) 将变为可用。因此, 探索分子间识别过程中的新的、特定的非共价键相互作用可能会在材料科学、催化、药物设计、超分子化学和晶体等不同领域开辟新的视角。工程.对于最近成为控制聚合和自组装现象的常规工具的预算外, 此情况为1,2,3,4,5。
根据 IUPAC 定义6: 当有证据表明在一个分子实体中与卤素原子相关的亲区域与另一个或相同的亲核区域之间有净吸引力的相互作用时, 就会发生卤素键,分子实体。在图 1中给出了预算外的示意图, 其中 X 是亲卤素原子 (路易斯酸, 预算外捐助者), Y 是电子密度的捐助者 (刘易斯基数, 预算外受体)。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55636/55636fig1.jpg"> 图 1: 卤素键的示意图表示形式。 亲卤素原子 (预算外-捐赠者) 与各种各样的分子支架 (R) 是共价键相连的, 而预算外受体 (Y) 可以是中性或阴离子的种类。此数字已从引用2中重印。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
乍一看, 这个定义似乎处理一些令人费解的方面, 因为卤素原子, 因为它们的高电负性, 通常被认为是高电子密度的地点。然而, 卤素原子作为 electrophiles 的行为是相当普遍的, 并且通过 "σ孔" 概念7的介绍, 优雅地合理化了 Politzer et .。
当卤素原子参与共价键时, 电子重分布发生, 电子密度成为各向异性8,9,10,11。原子的形状变成扁球形, 一个正静电电位区域 (所谓的σ孔) 沿着共价键的延伸发展, 在卤素原子的最外层 (图 2A)。这个正区域被一个负静电电位带所包围, 与共价键的正交。这个模型似乎解决了预算外的 "谜", 因为它解释了共价键结合卤素原子的非共价键相互作用模式, 以及相关的方向偏好, i. e, 与亲核试剂和侧向的线性相互作用与 electrophiles 的互动。
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55636/55636fig2.jpg"> 图 2: 卤素原子周围电子密度的各向异性分布.(A) 在共价键的卤素原子周围电子密度各向异性分布的示意图表示以及由此产生的相互作用的模式。(B) 等密度表面的分子静电电位图, 0.001 au 用于 cf 4、cf 3 Cl、cf 3 Br 和 cf 3 i. 颜色范围: 红色, 大于27大卡/摩尔;黄色, 在20和14大卡/摩尔之间;绿色, 在12和6大卡/摩尔之间;蓝色, 阴性此数字已从引用2中进行了修改。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
在设计功能超分子材料时, 预算外已迅速从科学的好奇心成长为最有趣的 noncovalent 互动之一12,13,14,15,16, 由于其独特的功能,即高方向性、可调谐的交互强度、疏水性和捐助者原子维度1。通过考虑σ孔的聚焦性质, 可以很容易地理解预算外的高方向性, 而交互强度经常与σ孔的大小相关。σ孔的尺寸 (空间范围) 和大小 (最大静电电位 VS、最大) 的值受卤素原子的极化和电负性和电子提取能力的影响。卤素17的邻域中的取代项 (图 2B)。作为一个普遍的趋势, 随着卤素原子变得更加极化, 取代分子变得更加电子化, 卤素σ孔变得更加正面。因此, 对于给定的 R, VS, max增加的顺序 F < Cl S, max变得更加正面。因此, haloperfluorocarbons, 特别是碘 perfluoroalkanes 和芳烃, 可以充当强大的预算外捐助者, 形成特别强的交互作用18,19,20 , 特别是疏水性加合物.
二十世纪九十年代下旬的21中报告了一例 PFC-HC 自组装给 cocrystals 的案例。在氯仿中混合摩尔量为 12-diiodotetrafluoroethane 和n、n、n'、n '-四甲基乙二胺时, 一个超分子复合体被隔离, 因为白色晶体在室温下稳定在空气中。单晶 x 射线分析表明, 在1维 (1D) 无限链中, 两个组分交替存在, 氮和碘原子之间的相互作用主要负责保持氟双碘的位置。这证明, 氮碘的预算外相互作用足够强, 以克服 PFC 和 HC 化合物之间存在的低亲和力, 并建议可以成功地利用预算外, 作为一个简单的途径引入氟化基团到任何新的超分子材料22,23,24, 包括液晶材料。
氟化取代剂, 事实上, 已成功地纳入液晶分子, 因为良好的稳定性, 由 C F 键, 以及小规模和低极化的氟原子, 这导致非常低的分子间色散相互作用25,26,27。此外, PFC 和 HC 链之间的隔离允许控制超分子液晶相, 增强了液晶材料的 smectic 特性28,29,30。一般理解, 物理/化学性质和 mesomorphism 都受到分子体系结构29,31的强烈影响。因此, 一个适当的分子设计是必不可少的产生新的超分子液晶具有量身定做的性质。这些软材料的基本主题是在一个相当刚性, 类似杆状的基团链接到一个或两个灵活的脂肪族链32,33,34。液晶化合物的传统设计主要是用中性种进行的, 但研究表明, 离子对也可以表现出液晶行为, 在离子液体和液体的界面上产生具有性质的材料。晶体35,36,37。
考虑到最近关于预算外液晶的结果24,38,39, 以及阴离子作为预算外受体的特定能力, 它似乎特别有趣的是利用这种非共价键的互动在设计新类型的签订。
1-烷基-3-咪唑碘 (1m) 的各种链长度, 称为离子液体40, 用于合成复合物 (图 3)41,42。请注意, 只有1-12, 轴承一个 C12 烷基链, 展出液体结晶度与 smectic a (Sm a) 相 (晶体 (Cr) 到 SmA 过渡温度 = 27 °c;Sm A 到各向同性液体 (ISO) 转折温度 = 80 °c;Cr ·27· SmA ·80· Iso)43。鎓盐的反应与 iodoperfluorooctane (2-8) 和 iodoperfluorodecane (2-10), 这是众所周知的预算外捐助者44,45。
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55636/55636fig3.jpg"> 图 3: 合成方案.启动离子液体的化学公式 (1-m)、iodoperfluoroalkanes (2-n) 和相关的预算外-络合物1-m•2-n.<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
碘化阴离子在 haloperfluoroalkanes44的超分子结构的形成中, 可望作为预算外受体参与。然而, 预测协调的预算外捐助物种的数量和拓扑结构仍然具有挑战性。事实上, 卤素阴离子通常涉及三 XBs46,47,48, 但更高的协调数也被观察到49,50。
在这里, 我们描述了一个获得高度氟化的预算外签订的程序和一个详细的程序, 以确定和描述预算外的发生。这里报告的分析序列和用于确定预算外的方法可被视为一般程序, 可用于任何类型的预算外系统的特性。

<table><tbody><tr><td>1-Methyl-imidazole&amp;nbsp;</td><td>Sigma-Aldrich</td><td>M50834-500G</td><td>liquid reagent</td></tr><tr><td>1-Iodoethane</td><td>Sigma-Aldrich</td><td>I7780-100G</td><td>liquid reagent</td></tr><tr><td>1-Iodobutane</td><td>Sigma-Aldrich</td><td>167304-100G</td><td>liquid reagent</td></tr><tr><td>1-Iodohexane</td><td>Sigma-Aldrich</td><td>238287-100G</td><td>liquid reagent</td></tr><tr><td>1-Iodooctane</td><td>Sigma-Aldrich</td><td>238295-25G</td><td>liquid reagent</td></tr><tr><td>1-Iododecane</td><td>Sigma-Aldrich</td><td>238252-100G</td><td>liquid reagent</td></tr><tr><td>1-Iodododecane</td><td>Sigma-Aldrich</td><td>238260-100G</td><td>liquid reagent</td></tr><tr><td>Acetonitrile</td><td>Sigma-Aldrich</td><td>271004-1L</td><td>organic solvent</td></tr><tr><td>Perfluorooctyl iodide&amp;nbsp;</td><td>Apollo Scientific</td><td>PC6170</td><td>fluorinated reagent/halogen-bond donor&amp;nbsp;</td></tr><tr><td>Perfluorodecyl iodide</td><td>Apollo Scientific</td><td>PC5970</td><td>fluorinated reagent/halogen-bond donor&amp;nbsp;</td></tr><tr><td>Bis(2,2,2-trifluoroethyl) ether&amp;nbsp;</td><td>Sigma-Aldrich</td><td>287571-5G</td><td>Internal standard for NMR</td></tr><tr><td>Chloroform-d</td><td>Sigma-Aldrich</td><td>151823-100G</td><td>Solvent for NMR</td></tr></tbody></table>

from molecules to materials: engineering new ionic liquid crystals through halogen bonding

在此, 我们证明了一种基于卤素键合 (XB) 的自底向上方法, 可以成功地应用于新型离子液晶 (签订) 的设计中。利用 haloperfluorocarbons 的高特异性和阴离子作为碘的能力, 我们获得了基于 1-烷基-3-咪唑 iodoperfluorocarbons 的超分子配合物, 克服了众所周知的碳氢化合物 (HCs) 与全氟化碳 (不混溶) 之间的相互关系。预算外的高方向性加上 fluorophobic 效应, 使我们能够获得 enantiotropic 液晶, 其中刚性, 非芳香, XB 超分子负离子作为液晶核心。
1-乙基-3-咪唑碘与 iodoperfluorooctane 的 x 射线结构分析表明存在层状结构, 这是众所周知的烷基链分离倾向的表现。这与观察 smectic mesophases 是一致的。此外, 所有报告的配合物融化低于100摄氏度, 大多数是液晶即使在室温下, 尽管起始材料是非液晶的性质。
这里所报道的超分子战略为基团设计提供了新的设计原则, 允许全新的功能材料类。

采用差分扫描量热法 (DSC)、POM 和热重分析 (TGA) 以及1H 和19F NMR 来表征所得到的络合物。1-2•2-8 的优质单晶在乙腈的起始组分的1:2 个解答获得了从溶剂的缓慢的蒸发在室温下。
DSC 分析了1-2 和2-8 与不同化学计量比率的混合物, 使我们可以得出鎓盐和 iodoperfluoroalkane 之间的正确协调化学成分为1:2。事实上,图 4A中的1:1 复杂度的 DSC 级数显示了 uncomplexed 鎓盐1-2 (峰值在57摄氏度) 的存在, 而在1:3 复合体中有一个多余的纯2-8 (熔点24°c)。另一方面, 1:2 复合体的级数显示出一个与起始化合物不同的峰值, 表明形成了一种新的纯晶体物种。
TGA 分析证实了这一结果。实际上, 只有在将1-12 和2-10 与1:2 比率混合后, 才获得了一个均匀样本, 它在比 uncomplexed iodoperfluorodecane 高的温度下定量地释放了氟化构造块 (图 5A 和 5B)。
19F 核磁共振作为一种简单、有效和灵敏的工具, 用于检测预算外加合物的形成。iodoperfluoroalkanes 电子亏碘与 i型-阴离子之间的 XB 强烈影响 CF2I 组 (δ = −60,0 ppm) 的信号, 并引起19F 核磁共振共振的可检测前场移位。测量复杂1-2•2-8 的Δδ值 1.2 ppm, 确认有吸引力的 noncovalent 相互作用涉及卤素原子作为亲物种 (图 6)。此外, 通过记录连续的1H 和19F 的核磁共振分析, 在22、2-trifluoroethyl 醚的存在下, 作为信号集成的内部标准, 预算外受体和捐助者模块之间的1:2 化学计量法进一步证实.
对1-2•2-8 的单晶 x 射线分析证实, 预算外驱动了三联超分子复合体的形成, 其中碘化阴离子作为二齿的 XB 受体, 结合了两个含氟链。I···I-距离几乎是相同的 [3.4582 (9) Å和 3.4625 (10) Å], 并且大致对应于27% 缩短关于碘原子和碘化阴离子的 vdW 和鲍林半径的总和, 分别为51。I···的高方向性被证实了。I-角度为 174.1 (1) °和 175.4 (2) °, 分别为 (图 7A)。两个同样居住的构象被观察为鎓阳离子, 近似地说谎在同一个平面和由一个非结晶性双重轴相关。图 7B 显示了离子和中性部件之间的分离, 以及在晶体内的 HC 和 PFC 链之间的分隔 (排除障碍)。
DSC 和 POM 的研究表明, 所有配合物在温度低于100摄氏度 (图 8A) 时熔化, 这是离子液体的典型特征。此外, 它们都显示了 enantiotropic 的液晶行为, 有些在室温下, 带有 SmB 和 SmA 相 (图 8A)。在冷却时, SmA-SmB 转换由风扇背面的特征条纹 (图 8B, 左) 标识。在过渡下的冷却过程中, 条纹消失了。
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/55636/55636fig4.jpg"> 图 4: 差分扫描量热。DSC thermograms 通过混合1-2 和2-8 在不同的化学计量比率中制备的样品: 1:3 样品 (顶部), 1:2 样品 (中间) 和1:1 样品 (底部)。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig4large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/55636/55636fig5.jpg"> 图 5:热分析.DSC 加热/冷却循环 (A) 和 TGA 分析 (B) 上的一个样本, 通过混合1-12 和2-10 在1:2 摩尔比率。此数字已从引用37中进行了修改。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/55636/55636fig6.jpg"> 图 6:19F 核磁共振分析.19F 核磁共振波谱在 CDCl3的2-8 (顶部) 和相关卤素结合的复杂1-2•2-8 (底部)。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig6large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/55636/55636fig7.jpg"> 图 7: x 射线单晶分析.(A) 复杂1-2•2-8 的非对称单元, 显示了三联 superanion 的形成, 其中两个氟化链与中央 I-阴离子相连 (报告了无序阳离子的单个 conformer);(B) 鎓盐1-2 和 iodoperfluorooctane 2-8 沿晶体B轴隔离;(C) 侧面视图, 显示结构的离子和氟碳区域。颜色代码: 灰色, 碳;蓝色, 氮气;洋红, 碘;绿色、氟;白色氢气卤素债券描绘为灰色线。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig7large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/55636/55636fig8.jpg"> 图 8: 偏振光学显微镜.(A)由热级 POM (蓝色为固态, 红色为 SmB, 橙色为 SmA) 的卤素粘结配合物的 thethermal 过渡的 1-m•2-n 的图表。(B) 为1-12•2-10 从各向同性状态冷却时观察到的 smectic 相的光学纹理。左: SmB 阶段在77°c;右: SmA 相在83°c。刻度条: 100 µm。此数字已从引用37中进行了修改。<a href="//cloudflare.jove.com/files/ftp_upload/55636/55636fig8large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody>
<tr>
<td></td>
			<td>光谱宽度 (赫)</td>
			<td>扫描号码</td>
			<td>脉冲延时 (s)</td>
		</tr>
<tr>
<td>1h</td>
			<td>7</td>
			<td>16</td>
			<td>1</td>
		</tr>
<tr>
<td>19f</td>
			<td>95</td>
			<td>16</td>
			<td>1</td>
		</tr>
</tbody></table>表 1: 获取参数1H 和19F 核磁共振实验

Watch this Scientific Journal Video about From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding at JoVE.com

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

一种基于卤素结合超分子阴离子的新型液晶聚合成协议 [C n F2 n +1-I···我·报告了nF2 n + 1]−。

从分子到材料: 通过卤素键合工程新的离子液体晶体

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid ...

from-molecules-to-materials-engineering-new-ionic-liquid-crystals

Research

Education

JoVE Journal

JoVE Core

Chemistry

Periodic Properties of the Elements

SCIENTISTS IN ACTION

68.9K 次观看.  Politecnico di Milano. 一种基于卤素结合超分子阴离子的新型液晶聚合成协议 [C n F2 n +1-I···我·报告了nF2 n + 1]−。

视频: From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form catalytically active N-Heterocyclic Carbenes (NHCs). Here we have used ILs as precatalysts in the addition of &#945;,&#946;-unsaturated aldehydes to chalcones to form 1,6-ketoesters, incorporating an anti-diphenyl moiety in a highly stereoselective fashion. The reaction has a broad substrate scope and several functional groups and heteroaromatics can be integrated into the ketoester backbone in generally good yields with maintained stereoselectivity. The reaction protocol is robust and scalable. The starting materials are inexpensive and the products can be obtained after simple filtration, avoiding solvent-demanding chromatography. Furthermore, the IL can be recycled up to 5 times without any loss of reactivity. Moreover, the 1,6-ketoester end product is a potent gelator in several hydrocarbon based solvents. The method enables rapid access to and evaluation of a new class of low molecular weight gelators (LMWGs) from recyclable and inexpensive starting materials.

Ionic liquids (ILs) mediate fast, simple and cheap access to 1,6-ketoesters in high diastereoselectivities and good yields. The reaction protocol is robust and the 1,6-ketoesters can be obtained in gram scale after a simple filtration protocol. Moreover, the 1,6-ketoesters are potent gelators in hydrocarbon solvents.

1,6-酮酯高立体选择性合成离子液体介导:三组分反应启用快速进入低分子量胶凝剂的新型类

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form ...

科研

化学

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline elastomers (LCEs) with facile control over network structure and programming of an aligned monodomain. Tailored LCE networks were synthesized using routine mixing of commercially available starting materials and pouring monomer solutions into molds to cure. An initial polydomain LCE network is formed via a self-limiting thiol-acrylate Michael-addition reaction. Strain-to-failure and glass transition behavior were investigated as a function of crosslinking monomer, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). An example non-stoichiometric system of 15 mol% PETMP thiol groups and an excess of 15 mol% acrylate groups was used to demonstrate the robust nature of the material. The LCE formed an aligned and transparent monodomain when stretched, with a maximum failure strain over 600%. Stretched LCE samples were able to demonstrate both stress-driven thermal actuation when held under a constant bias stress or the shape-memory effect when stretched and unloaded. A permanently programmed monodomain was achieved via a second-stage photopolymerization reaction of the excess acrylate groups when the sample was in the stretched state. LCE samples were photo-cured and programmed at 100%, 200%, 300%, and 400% strain, with all samples demonstrating over 90% shape fixity when unloaded. The magnitude of total stress-free actuation increased from 35% to 115% with increased programming strain. Overall, the two-stage TAMAP methodology is presented as a powerful tool to prepare main-chain LCE systems and explore structure-property-performance relationships in these fascinating stimuli-sensitive materials.

A novel methodology is presented to synthesize and program main-chain liquid-crystalline elastomers using commercially available starting monomers. A wide range of thermomechanical properties was tailored by adjusting the amount of crosslinker, while the actuation performance was dependent on the amount of applied strain during programming.

的可编程主链液晶性弹性体用双级硫醇丙烯酸酯反应合成

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline ...

Synthesis of Ionic Liquid Based Electrolytes, Assembly of Li-ion Batteries, and Measurements of Performance at High Temperature

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion batteries for use in devices operating at elevated temperatures require thermally stable and non-flammable electrolytes. Ionic liquids (ILs), which are non-flammable, non-volatile, thermally stable molten salts, are an ideal replacement for flammable and low boiling point organic solvent electrolytes currently used today. We herein describe the procedures to: 1) synthesize mono- and di-phosphonium ionic liquids paired with chloride or bis(trifluoromethane)sulfonimide (TFSI) anions; 2) measure the thermal properties and stability of these ionic liquids by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); 3) measure the electrochemical properties of the ionic liquids by cyclic voltammetry (CV); 4) prepare electrolytes containing lithium bis(trifluoromethane)sulfonamide; 5) measure the conductivity of the electrolytes as a function of temperature; 6) assemble a coin cell battery with two of the electrolytes along with a Li metal anode and LiCoO2 cathode; and 7) evaluate battery performance at 100 &#176;C. We additionally describe the challenges in execution as well as the insights gained from performing these experiments.

Here, we describe protocols to prepare phosphonium-based ionic liquid and lithium bis(trifluoromethane)sulfonimide salt electrolytes, and assemble a non-flammable and high temperature functioning lithium-ion coin cell battery.

离子液体基电解质的合成，装配锂离子电池，并在高温性能的测量

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion ...

工程学

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

由界面润湿片的热力学生长触发的液晶中的定向转变

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

光诱导的宏观振荡运动液晶网络的制备

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

观测 Photoresponsive 液晶结构动力学的新方法

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

液晶中磁调谐铁电极化的测量

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

一种用于快速和低压彩色调制的电化学胆固醇液晶器件

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

单域液晶的弹性体和液晶橡胶纳米复合材料的制备

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

生物工程

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

扭曲弯曲的液晶的高对比度和快速光圈开关

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...