Self-Assembly DOI: 10.1002/ange.200805202 Economical Design in Noncovalent Nanoscale Synthesis: Diverse Photofunctional Nanostructures Based on a Single Covalent Building Block** Galina Golubkov, Haim Weissman, Elijah Shirman, SharonG. Wolf, Iddo Pinkas, and Boris Rybtchinski* Noncovalent synthesis is an efficient “bottom-up” method- ology for the construction of organic nanoscale systems by the self-assembly of covalent molecular building blocks. [1–3] The design of noncovalent systems takes advantage of encoding complexity in an economical way: a simple construction unit elicits the structure and function of the extended supramolec- ular arrays. This methodology can be further enhanced if a single generic covalent building block can be utilized for many structural and functional motifs; such a “molecular economy” approach being analogous to biological systems. The economical design of organic nanostructures has there- fore attracted much interest [3–7] as it can further reduce the need of time-consuming covalent synthesis, and thus facili- tates the screening and optimization of organic nanoscale systems. Herein we report the assembly of nanoscale ribbons, vesicles, tubes, and platelets, all based on a single generic covalent building block. Such diversity is achieved by using a two-stage self-assembly motif that is conveniently regulated through metal coordination. The nanostructures show good exciton mobility and can be utilized as light-harvesting systems. Efficient generation of diverse nanostructures based on a single covalent building block requires a built-in functionality that can be expediently modified, which leads to changes in overall structure. By utilizing this concept, we have recently shown that the supramolecular fibers based on amphiphilic perylene diimide (PDI) units can undergo depolymerization (micelle formation) upon chemical reduction of PDIs, while oxidation with air restores the fibers. [8] This represents an interesting example of reversible supramolecular depolyme- rization, yet it is based on a single type of input—the reduction of a PDI unit. To achieve a high degree of diversity, a system that allows multiple inputs is required. Conse- quently, we aimed to introduce two levels of self-assembly encoding in a covalent building block: a general permanent self-assembly motif, and a tunable motif that has a broad range of possible modifications. We also aimed to produce a system in which self-assembly brings about useful photo- function. In pursuit of this idea, compound 1 (Scheme 1), our primary building block, was designed to possess an amphi- philic photoactive moiety and a ligand that is capable of binding a wide variety of metal centers (a unit for tuning). Thus, 1 consists of three principal components that are covalently linked: The strongly hydrophobic PDI chromo- phore (photofunctional unit), a hydrophilic polyethylene glycol (PEG) group, and the terpyridine (terpy) as a metal- coordinating moiety (the syntheses and characterization of compounds 1–4 are described in the Supporting Information). PEGylated amphiphilic PDIs are very advantageous self- assembling units because of strong hydrophobic interactions between PDI cores in aqueous medium. [7, 9, 10] In a water/THF mixture (9:1 v/v), compound 1 self- assembles into long fibers (Figure 1 a) as evidenced by cryogenic transmission electron microscopy (cryo-TEM). The fibers show a ribbonlike structure, and an occasional twisting of the ribbons from their narrower, high-contrast edges ((4 Æ 0.6) nm) to their wider, low-contrast faces ((7.9 Æ 1.3) nm) is observed (Figure 1a, white arrows). The length of the fibers is difficult to estimate as their end caps cannot be identified. Most of the fibers appear to extend over the entire cryo-TEM image and probably reach several microns in length. The aligned, tightly packed fibers exhibit a fiber-to-fiber spacing of (7.1 Æ 0.8) nm (Figure 1 a), which corresponds to a high-contrast ordered aromatic core (responsible for fiber images in cryo-TEM) and low-contrast solvated PEGs (interfiber area). Individual fibers show a segmented struc- ture (see inset in Figure 1 a), such hierarchical structures with segmented cores are uncommon. [11, 12] Notably, the 1.9 nm segment periodicity is almost identical throughout all struc- tures and corresponds well to the dimensions of the PDI. A [*] Dr. G. Golubkov, Dr. H. Weissman, E. Shirman, Dr. B. Rybtchinski Department of Organic Chemistry Weizmann Institute of Science, Rehovot 76100 (Israel) Fax: (+ 972) 8-934-4142 E-mail: boris.rybtchinski@weizmann.ac.il Homepage: http://www.weizmann.ac.il/oc/boris/ Dr. I. Pinkas Department of Plant Sciences Weizmann Institute of Science (Israel) Dr. S. G. Wolf Department of Chemical Research Support Weizmann Institute of Science (Israel) [**] This work was supported by grants from the Israel Science Foundation (grant no. 917/06) and the Helen and Martin Kimmel Center for Molecular Design. The cryo-TEM studies were conducted at the Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging (Weizmann Institute). Transient absorption studies were performed at the Dr. J. Trachtenberg Laboratory for Photobiology and Photobiotechnology (Weizmann Institute) and were supported by a grant from S. Zuckermanof (Toronto, Canada). We thank Prof. R. Neumann for the access to modeling software. B.R. holds the Abraham and Jennie Fialkow Career Development Chair. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200805202. Zuschriften 944  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2009, 121, 944 –948