Journal
LANGMUIR
Volume 25, Issue 5, Pages 2913-2923Publisher
AMER CHEMICAL SOC
DOI: 10.1021/la803811w
Keywords
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Funding
- National Science Foundation [CHE0616474]
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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.
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