Nanotube Self-Assembly DOI: 10.1002/anie.201003415 Amphiphilic Self-Assembly of an n-Type Nanotube** Hui Shao, James Seifert, Natalie C. Romano, Min Gao, JonathanJ. Helmus, Christopher P. Jaroniec, David A. Modarelli, and Jon R. Parquette* The electronic properties of p-conjugated materials depend on the nature of the interactions among the constituent chromophores. [1] The p–p stacking interactions present in aggregated arrays of semiconductors provide pathways for charge transport and energy migration. [2] Thus, the self- assembly of p-conjugated building blocks into discrete, one- dimensional (1D) nanostructures is a powerful strategy to tune the properties of organic electronic materials. [3] The majority of these approaches have produced twisted nano- fibers of p-type chromophores. The exceptional electronic characteristics of carbon nanotubes [4] have also inspired interest in versatile supramolecular approaches toward p-conjugated nanotubes. [5] The availability of self-assembled organic nanotubes would provide greater modularity in their design and functionalization. However, examples of p-con- jugated systems that assemble into well-defined nanotubes are relatively uncommon. [6] Herein, we describe a 1D n-type nanotube formed by the bolaamphiphilic [7] self-assembly of 1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI) with l-lysine headgroups (Figure 1). We recently reported a simple method for fabricating n-type 1D nanostructures by the b-sheet assembly of dipep- tide–NDI conjugates [8] into either helical nanofibers or twisted nanoribbons. [9] Time-resolved fluorescence aniso- tropy experiments showed enhanced energy migration within these nanostructures. Herein, we explore how the intermolecular electrostatic interactions derived from the lysine headgroups [10] in bolaamphiphile A (Figure 1 a), in conjunction with p–p association among the NDI chromo- phores, drive the self-assembly process in water [11, 12] toward soluble, well-ordered 1D nanotubes. Bolaamphiphile A was constructed by imidation of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride with two equivalents of Boc-l-lysine, followed by TFA deprotec- tion (Supporting Information, Scheme S1). Bolaamphiphile A formed a transparent gel in water at concentrations as low as 1 % (w/w) (1.9 mm ; Figure 1b, red inset), and was stable in the gel state for several months. Transmission electron microscopy (TEM) of a negatively stained sample of A revealed the formation of micrometer-long nanotubes with uniform diameters of (12  1) nm (Figure 1 b). The nanotubes appeared as two white, parallel lines separated by a dark center, which is consistent with the cross-sectional view of a hollow tubular structure filled with the negative stain, uranyl acetate (Figure 1 b). [13] The thickness of the wall was approx- imately (2.5  0.5) nm. A few nanorings, albeit rare, could also be observed in the TEM images (red arrows in Figure 1 b), with external diameters of 12 nm and wall thicknesses of 2.5 nm, which are identical with the nanotube dimensions. Tapping-mode AFM imaging of dilute bolaamphiphile A gel samples (250 mm) on mica also revealed high-aspect ratio assemblies with cross-sectional heights of about 9 nm, which were slightly smaller than those observed by TEM ; this effect Figure 1. a) Structures of lysine-based bolaamphiphiles A (R = O  ) and B (R = OMe) and the assembly of A into rings, which stack to give tubes. The blue sections of A undergo hydrophobic p–p stacking interactions, and the red sections electrostatic interactions. b) TEM image of bolaamphiphile A in water (250 mm; carbon-coated copper grid); 2 % (w/w) uranyl acetate as negative stain. Blue insets: Two nanotubes and one nanoring. c) Tapping-mode AFM image of bola- amphiphile A in water (250 mm) on freshly cleaved mica. Red inset: Section analysis showing uniform height of the assemblies. Height indicated by red arrows: ca. 9 nm. [*] H. Shao, J. Seifert, M. Gao, J. J. Helmus, Prof. C. P. Jaroniec, Prof. J. R. Parquette Department of Chemistry, The Ohio State University 100 W. 18th Ave., Columbus, OH 43210 (USA) E-mail: parquett@chemistry.ohio-state.edu N. C. Romano, Prof. D. A. Modarelli Department of Chemistry and The Center for Laser and Optical Spectroscopy The University of Akron (USA) [**] This work was supported by the National Science Foundation (CHE-0750004 and CRC-CHE-526864). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201003415. Communications 7688  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2010, 49, 7688 –7691