Analysis of the spatial dimensions of fully aromatic dendrimers
Analysis of the spatial dimensions of fully aromatic dendrimers
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DOI：
10.1002/anie.200351810
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Lindner, P
中科院分区：
文献类型：
--
作者：
Rosenfeldt, S;Dingenouts, N;Lindner, P
树枝状大分子由于其规则的分支结构和不寻常的性质而成为一类迷人的分子。[1-4]迄今为止描述的大多数树枝状聚合物由柔性重复单元组成。这样的分子可以呈现出大量的构象，这些构象是通过围绕这些单元之间的键旋转而产生的（图1b）。特别地，末端基团可以折叠回到分子的内部。当考虑刚性的、完全芳香的树枝状聚合物G4-M时，会出现完全不同的情况（图1a）：在这种情况下，苯环要么是线性的，要么彼此形成608或1208的角度。因此，围绕环之间的键的旋转不能深刻地改变分子的结构。图1 B中所示的结构表明了柔性树枝状聚合物的“致密壳”结构，其由被密集堆积的端基壳封闭的中空核组成。这种树枝状的盒子可以用作分子容器。因此，许多关于树枝状聚合物可能应用的想法都起源于这张照片。[1-3]这些想法进一步鼓励了早期出版的德热内和Hervet，其中第一次理论治疗这种致密的结构。[5]然而，随后的理论工作已经令人信服地证明，柔性树枝状聚合物在分子的核心中表现出其最大密度（“致密核心模型”），并且端基位于分子内任何位置的概率有限。[6-9]小角中子散射（SANS [10]）的实验研究已经完全证实了这一结果（参见参考文献[11]中对这项工作的评论）。在
Dendrimers present a fascinating class of molecules because of their regularly branched structure and their unusual properties.[1–4] Most of the dendrimers described so far are composed of flexible repeating units. Such a molecule can assume a vast number of conformations that are generated by rotation about the bonds between these units (Figure 1b). In particular, the terminal groups can fold back into the interior of the molecule. A totally different situation arises when considering the stiff, fully aromatic dendrimer G4-M (Figure 1a): In this case the benzene rings are either linear or form an angle of 608 or 1208 to each other. Therefore, rotation about the bonds between the rings cannot change the structure of the molecule profoundly. Most importantly, no backfolding of the terminal groups is possible in such a molecule.The structure shown in Figure 1 b suggests a “dense-shell” structure of flexible dendrimers, which consists of a hollow core closed by a densely packed shell of end groups. Such a dendritic box could be used, for example, as a molecular container. Hence, many ideas for possible applications of dendrimers originated from this picture.[1–3] These ideas were further encouraged by an early publication by de Gennes and Hervet in which the first theoretical treatment of such denseshell structures was presented.[5] Subsequent theoretical work, however, has demonstrated convincingly that flexible dendrimers exhibit their maximum density in the core of the molecule (“dense-core model”) and that there is a finite probability for the end groups to be located at any position within the molecule.[6–9] Experimental studies by small-angle neutron scattering (SANS [10]) have fully corroborated this result (see the review of this work in reference [11]). In