Tong Wenjun, Wei Yanhu, Armbrust Kurt W, Zimmt Matthew B
Department of Chemistry, Brown University Providence, Rhode Island 02912, USA.
Langmuir. 2009 Mar 3;25(5):2913-23. doi: 10.1021/la803811w.
Scanning tunneling microscopy (STM) is used to determine the 2-D unit cell parameters of monolayers self-assembled by twelve symmetrical, 1,5-bis(linear aliphatic ether side chain) anthracenes at the solution-graphite interface. The standard morphology assembled by 1,5-bis(alkyloxymethyl) anthracenes consists of single-lamella domains containing columns of anthracene cores alternating with columns of interdigitated, aliphatic side chains. Adjacent side chains within the aliphatic columns adsorb in antiparallel orientations. The terminal methyl (omega-position) of each side chain lies in registration with the 2-positions of its two neighboring chains ((omega <--> 2)-packing). Anthracenes with diether side chains can generate repulsive or attractive dipole-dipole interactions between proximate ethers of adjacent aliphatic chains. Anthracenes bearing even length side chains with oxygens at the 2- and omega-1 positions or at the 3- and omega-2 positions do not assemble (omega <--> 2)-packed monolayers. Repulsive dipolar interactions between ethers in adjacent side chains raise the energy of (omega <--> 2) morphologies. These "self-repulsive" side chains drive assembly of (omega <--> l)- or (omega <--> 3)-packed morphologies, which enjoy stabilizing dipolar interactions between ethers in adjacent side chains. In stark contrast, anthracenes bearing odd length diether side chains assemble (omega <--> 2)-packed morphologies, regardless of whether adjacent chains suffer zero, one, or two sets of proximate dipole-dipole repulsions. The intrinsic energy gap from (omega <--> 2)- to non-(omega <--> 2)-packed morphologies of odd length side chain anthracenes is, apparently, larger than for even length side chain anthracenes. Overall, the twelve compounds self-assemble seven different morphologies. Distinguishing morphologies, understanding polymorphism within the monolayers, and evaluating the morphological consequences of side chain dipolar interactions is facilitated by viewing the monolayers as assemblies of 1-D, molecular tapes.
扫描隧道显微镜（STM）用于确定由十二个对称的1,5-双（线性脂肪醚侧链）蒽在溶液-石墨界面自组装形成的单层的二维晶胞参数。由1,5-双（烷氧基甲基）蒽组装而成的标准形态由单层薄片域组成，其中蒽核柱与相互交错的脂肪族侧链柱交替排列。脂肪族柱内相邻的侧链以反平行取向吸附。每个侧链的末端甲基（ω位）与其两个相邻链的2位对齐（（ω⇄2）堆积）。带有二醚侧链的蒽可以在相邻脂肪族链的相邻醚之间产生排斥或吸引的偶极-偶极相互作用。在2位和ω-1位或3位和ω-2位带有偶数长度且带有氧原子的侧链的蒽不会组装成（ω⇄2）堆积的单层。相邻侧链中醚之间的排斥偶极相互作用提高了（ω⇄2）形态的能量。这些“自排斥”侧链驱动（ω⇄1）或（ω⇄3）堆积形态的组装，这种形态在相邻侧链的醚之间具有稳定的偶极相互作用。与之形成鲜明对比的是，带有奇数长度二醚侧链的蒽会组装成（ω⇄2）堆积形态，无论相邻链是否遭受零组、一组或两组相邻偶极-偶极排斥。奇数长度侧链蒽从（ω⇄2）堆积形态到非（ω⇄2）堆积形态的固有能隙显然比偶数长度侧链蒽的更大。总体而言，这十二种化合物自组装形成七种不同的形态。将单层视为一维分子带的组装有助于区分形态、理解单层内的多晶型现象以及评估侧链偶极相互作用的形态学后果。
