J. Phys. Chem. C 2009, 113, 3929–3933
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Self-Assembled Organic Functional Nanotubes and Nanorods and Their Sensory Properties Yongwei Huang,†,‡ Baogang Quan,† Zhixiang Wei,*,† Guangtong Liu,† and Lianfeng Sun† National Center for Nanoscience and Technology, Beijing, 100190, People’s Republic of China, and Graduate School of the Chinese Academy of Sciences, Beijing, 100039, People’s Republic of China ReceiVed: September 3, 2008; ReVised Manuscript ReceiVed: January 3, 2009
Self-assembled, one-dimensional nanostructures of N,N′-bis(2-(trimethylammonium iodide)ethylene)perylene3,4,9,10-tetracarboxyldiimide (PTCDI-I) with tunable morphologies were successfully prepared by a facile evaporation method. PTCDI-I nanotubes with diameters of approximately 100-300 nm were obtained by the evaporation of the aqueous solution of PTCDI-I, while long nanorods with diameters of approximately 200-300 nm were produced by slow evaporation of the methanolic solution of PTCDI-I. Studies of the nanostructures formed at different stages suggested that the formation of nanotubes and nanorods could be ascribed to different crystallization processes from different solutions. The PTCDI-I nanostructures were redox-active, and fourprobe measurements based on a single nanotube or nanorod exhibited resistance decreased by 2 to 3 orders of magnitude after being exposed to reducing agents such as hydrazine or phenylhydrazine. Such high resistance modulations indicate that these nanostructures will be useful as building blocks for electronic nanodevices and sensors. Introduction The ability to prepare nanostructures with defined morphologies and sizes on a bulk scale is an essential requirement for application of nanostructures. Therefore, extensive efforts have been devoted to developing synthetic strategies to produce nanostructures with tailored electronic and photonic properties.1 However, to date, most studies focused on inorganic nanostructures with controlled morphologies.2 Nanostructures of organic molecules have attracted more attention recently due to their tunable optical and electrical properties,3 and their potential application in various fields, such as optoelectronics, catalysis, energy storage, and sensors.4 Because morphology and size of organic nanostructures play an important role in determining their properties, developing a facile preparation method by which their morphology and size can be controlled is important to elucidating their morphology-property relationships. Perylene tertracarboxylic diimide (PTCDI) derivatives are of interest because of their n-type semiconducting characteristics,5 and their wide applications in organic field-effect transistors (OFETs)6 and fluorescence sensors.7 Self-assembly of PTCDI derivatives into various nanostructures, including nanobelts,8 nanotubes,9 and nanofibers,10 has been extensively studied. For instance, Zang et al. reported nanowires and nanobelts of PTCDI derivatives produced by precipitation or evaporation methods,8,11 which could be used for probing organic amines by electrical or fluorescent signals.8c,d,12 However, most self-assembled PTCDI nanostructures are based on organic soluble molecules, whereas self-assembled nanostructures of ionic PTCDI derivatives and their properties have not been studied in detail. Herein, a facile route to prepare nanotubes and nanorods of N,N′-bis(2-(trimethylammonium iodide)ethylene)perylene-3,4,9,10tetracarboxyldiimide (PTCDI-I, Scheme 1) by a solvent evaporation method is reported. The nanostructure morphologies were controlled by varying solvents from water to methanol. The self* Corresponding author. Phone: + 86-10-8254 5565. Fax: + 86-10-6265 6765. E-mail:
[email protected]. † National Center for Nanoscience and Technology. ‡ Graduate School of the Chinese Academy of Sciences.
SCHEME 1: Chemical Structure of N,N′-Bis(2-(trimethylammonium iodide)ethylene)perylene-3,4,9,10-tetracarboxyldiimide (PTCDI-I)
assembled PTCDI-I nanostructures generated from solutions of water and methanol were studied by various techniques including ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In addition, the sensory properties of devices based on a single nanotube and nanorod were successfully achieved by electrical measurement. The conductivity of PTCDI-I nanostructures showed a morphology-dependent sensitivity to hydrazine and phenylhydrazine vapors. Experimental Section N,N′-Bis(2-(trimethylammonium iodide)ethylene)perylene3,4,9,10-tetracarboxyldiimide (PTCDI -I) was synthesized according to a published procedure.13 Ultrapure water with a resistance of 18.2 MΩ · cm was generated with a Milli-Q apparatus (Millipore) and filtered by using an inorganic membrane with a pore size of 0.02 µm (Whatman International, Ltd.). Methanol, hydrazine hydrate solution (85%), and phenylhydrazine were obtained from Beijing Chemical Agent, Inc., and were used as received without further purification. The PTCDI-I solution was prepared by dissolving the PTCDI-I powder into water or methanol (0.3 mM). After being stirred for 3 min, the samples were left undisturbed for approximately 24 h at room temperature. Preparation of a device for current-voltage measurement required three steps. First, 100 nm thick Pt electrode pads were deposited on a thermally oxidized silicon substrate by conventional photolithography, electron beam evaporation, and a lift-off process. Subsequently,
10.1021/jp8078452 CCC: $40.75 2009 American Chemical Society Published on Web 02/12/2009
3930 J. Phys. Chem. C, Vol. 113, No. 10, 2009
Huang et al.
Figure 2. XRD patterns of PTCDI-I nanotubes (black curve) and nanorods (red curve). Figure 1. (a and b) SEM images of nanotubes and nanorods formed respectively from PTCDI-I aqueous solution and methanolic solutions (0.3 mM); (c and d) TEM images of PTCDI-I nanotubes and nanorods.
a drop of PTCDI-I solution (10 µL) was added to the substrate. Individual PTCDI-I nanotubes and nanorods formed on the surface of the substrate after solvent evaporation. Pt electrodes of 100 nm in width and 150 nm in thickness were successfully deposited by using electron beam-induced deposition, using a focused ion beam (FIB) system (FEI Company, Dual Beam Nova NanoLab 200) at an electron energy of 5 KeV and a beam current of 0.4 nA, respectively. The sizes and shapes of the nanostructures were observed by a field-emission SEM (FESEM, Hitachi S-4800) operated at an accelerating voltage of 6 kV. For SEM studies, a drop of the sample (10 µL) was added onto silicon substrates, and the aqueous solution was allowed to evaporate in air at room temperature while the methanolic solution was allowed to evaporate in a sealed jar at room temperature. To minimize sample charging, samples were coated with a thin layer of gold (
