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    Synthesis and Characterization of Monolayers and Langmuir-Blodgett Films of an Amphiphilic Oligo(ethylene glycol)-C60-hexadecaaniline Conjugate

    Year: 2006

    Journal: Langmuir, 2006, 22 (12), pp 5366–5373, 20111221

    Authors: Zhexiong Tang, Prashant A. Padmawar, Taizoon Canteenwala, Yuan Gao, Erik Watkins, Jaroslaw Majewski, Long Y. Chiang, and Hsing-Lin Wang

    Organizations: MSJ586, C-PCS, Chemistry Division and Los Alamos Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Department of Chemistry, University of MassachusettsLowell, Lowell, Massachusetts 01854

    A novel amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline (A16) tricomponent conjugate, C60>(A16-EG43), possessing a well-defined number of repeating aniline donor units and a hydrophilic ethylene glycol oligomer chain was synthesized. The compound is composed of a covalently bound donor−acceptor chromophore structure. Molecular self-assembly of C60>(A16-EG43) at the air−water interface formed a densely packed Langmuir monolayer with all highly hydrophobic fullerene cages located above the liquid interface. The monolayer can then be transferred onto a glass substrate via Langmuir−Blodgett (LB) deposition. LB multilayered thin films formed by multiple deposition of the monolayer yielded broadened optical absorption peaks extending beyond 600 nm into the 950 nm region, suggesting strong intermolecular interactions among the C60 cages and the A16 moieties. An X-ray reflectometry study clearly reveals that the Langmuir film at the air−water interface consists of a C60 top layer and a bottom layer containing hexcadecaaniline and oligo(ethylene glycol) with gradually decreasing electron density over a distance of approximately 130 Å above bulk water. The pressure isotherm shows that the packing density of the C60>(A16-EG43) monolayer, corresponding to a molecular area of 95 Å2/molecule, is similar to that of the surface area of the C60 monolayer. This result suggests that C60 packing plays a dominant role in guiding the formation of the monolayer structure. Further photoexcitation of hexadecaaniline moieties of aligned (C60>)-A16 layers by a flash light source induces cross linking between adjacent A16 segments forming an interlinked A16 array. Our results have demonstrated a unique fabrication method for preparing the aligned donor−acceptor array using strong intermolecular interactions between fullerenes as the molecular orientation guiding force in the Langmuir−Blodgett technique.