Dipolar Side Chain Control of Monolayer Morphology: Symmetrically Substituted 1,5-(Mono- and diether) Anthracenes at the Solution-HOPG Interface

作者：Tong Wenjun; Wei Yanhu; Armbrust Kurt W; Zimmt Matthew B^*

来源：Langmuir, 2009, 25(5): 2913-2923.

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 <-> 1)- 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 surfer 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 I-D, molecular tapes.

• 出版日期2009-3-3