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    Langmuir and Langmuir-Blodgett Films of Amphiphilic Bistable Rotaxanes

    Year: 2004

    Journal: Langmuir 2004, 20, 5809-5828, 20111221

    Authors: Isaac C. Lee, Curtis W. Frank, Tohru Yamamoto, Hsian-Rong Tseng, Amar H. Flood, J. Fraser Stoddart and Jan O. Jeppesen

    Organizations: aCenter on Polymer Interfaces and Macromolecular Assemblies and Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025 bThe California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569 cDepartment of Chemistry, Odense University (University of South Denmark), Campusvej 55, DK-5230, Odense M, Denmark

    A series of amphiphilic bistable [2]rotaxanessin which a ring-shaped component, the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), has been assembled around two recognition sites, a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) ring system, situated apart at different strategic locations within the central polyether section of an amphiphilic dumbbell component that is terminated by a hydrophobic tetraarylmethane-based stopper (near the TTF unit) at one end and by a hydrophilic tetraarylmethane-based stopper (near the DNP ring system) at the other endshas been designed and synthesized.Theeffects of systematic changes in the constitutions of the three ethylene glycol tails (diethylene or tetraethylene glycol) and end groups (hydroxyl or methoxyl functions) attached to the hydrophilic stoppers on Langmuir film balance and surface rheology experiments at 20 °C were examined to determine the monolayer stabilities and co-conformations of the [2]rotaxanes and their free dumbbell counterparts. These experiments allow us to propose a model for the rotaxane's structures at different surface pressures. All the [2]rotaxanes form stable Langmuir films. These films typically pass from a liquid-expanded region to a liquid-condensed region. The transition between the two regionswaseither directly observed or ascertained using film stability experiments. Film balance and surface rheology experiments showed that the addition of the tetracationic cyclophane component and hydroxyl end groups markedly increased the stabilities and viscoelasticity of the films.