Langmuir-Blodgett films of One-dimensional Nanowires composed of Amphiphilic Tetrathiafulvalenes and Electron Acceptor
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Langmuir-Blodgett films of One-dimensional Nanowires composed of Amphiphilic Tetrathiafulvalenes and Electron Acceptor Yoko TATEWAKI1, Junko TAKIZAWA1, Tatsuya HATANAKA2, Mutsumi KIMURA1,2 and Hirofusa SHIRAI1 1 Collaborative Innovation Center for Nanotech FIBER, Shinshu University, Ueda 386-8567, Japan 2 Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan ABSTRACT We found that novel amphiphilic tetrathiafulvalene (TTF; 1) organized into supramolecular assemblies by the addition of electron acceptor 2,3,5,6-tetrafluoro-7,7’,8,8’tetracyano-p-quinodimethane (F4TCNQ) at the air-water interface. The assemblies on the airwater interface can be transferred onto the surface of mica and the morphologies of transferred films were investigated by AFM. The morphology of Langmuir-Blodgett films strongly depended on the ratio between 1 and F4TCNQ. Film of 1 : 1 mixture of 1 and F4TCNQ formed nanoscopic wires having an average dimension of 5.0 (height) x 70 (width) x 3000 (length) nm. On the other hand, the film of 2 : 1 mixture of 1 and F4TCNQ showed the mixed domains of wires and flat monolayers. Thus, the completely charge-transferred complex (1+)(F4TCNQ-) formed one-dimensional nanowires having a micrometer length. Room temperature electrical conductivities of cast film for 1 : 1 and 2 : 1 mixed layers of 1 and F4TCNQ were 2.4 x 10-4 and 8.0 x 10-5 S cm-1, respectively. INTRODUCTION One dimensional nano-strucrures like nanowire and nanotube are one of important building-components in nanodevices [1,2]. Molecular-assembly nanomaterials are constructed utilizing intermolecular interactions such as charge-transfer (CT), hydrogen-bonding and coordinate bonding interactions [3-6]. The Langmuir-Blodgett (LB) technique is promising for building a conduction path. This technique provides a way of arranging the molecules in a fixed configuration, which can enhance the occurrence of intermolecular interactions. These characteristics of the LB method can give rise to well ordered monolayer packing in a two dimensional layer [7]. Here we reported the LB films composed of different mixing ratio. The morphologies in mixing ratio between 1 and F4TCNQ from 1 : 1 to 2 : 1 are expected to change the shape of surface domains and electronic state[8]. EXPERIMENT The structures of 1 and F4TCNQ were shown in Scheme 1. 1 was prepared by the procedure described elsewhere [9,10]. F4TCNQ was purchased from Tokyo Chemical Industry Co., LTD. The Langmuir films at the air-water interface and the LB films were prepared by using a conventional LB trough (USI, USI-3-22) equipped with two symmetrical moving barriers. Pure water was used as a subphase. The charge transfer complex solution of 1 and
F4TCNQ was prepared by mixing of 1 in CHCl3 (1 mM) with F4TCNQ in CH3CN (1 mM). This solution was spread on the pure water. The floating monolayers were remaining for 20 min after spreading of solution. Surface pressure-area per molecule (π - A) isothermes were recorded at 291
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