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      Directed assembly of optoelectronically active alkyl-π-conjugated molecules by adding n-alkanes or π-conjugated species.

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          Abstract

          Supramolecular assembly can yield ordered structures by taking advantage of the cumulative effect of multiple non-covalent interactions between adjacent molecules. The thermodynamic origin of many self-assembled structures in water is the balance between the hydrophilic and hydrophobic segments of the molecule. Here, we show that this approach can be generalized to use solvophobic and solvophilic segments of fully hydrophobic alkylated fullerene molecules. Addition of n-alkanes results in their assembly--due to the antipathy of C60 towards n-alkanes--into micelles and hexagonally packed gel-fibres containing insulated C60 nanowires. The addition of pristine C60 instead directs the assembly into lamellar mesophases by increasing the proportion of π-conjugated material in the mixture. The assembled structures contain a large fraction of optoelectronically active material and exhibit comparably high photoconductivities. This method is shown to be applicable to several alkyl-π-conjugated molecules, and can be used to construct organized functional materials with π-conjugated sections.

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          Self-organization of supramolecular helical dendrimers into complex electronic materials.

          The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores pi-stacks of donors, acceptors or donor-acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor-acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive pi-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications.
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            Design strategies for organic semiconductors beyond the molecular formula.

            Organic semiconducting materials based on polymers and molecular systems containing an electronically delocalized structure are the basis of emerging optoelectronic technologies such as plastic solar cells and flexible transistors. For isolated molecules, guidelines exist that rely on the molecular formula to tailor the frontier (highest occupied or lowest unoccupied) molecular orbital energy levels and optical absorption profiles. Much less control can be achieved over relevant properties, however, as one makes the transition to the ensemble behaviour characteristic of the solid state. Polymeric materials are also challenging owing to the statistical description of the average number of repeat units. Here we draw attention to the limitations of molecular formulae as predictive tools for achieving properties relevant to device performances. Illustrative examples highlight the relevance of organization across multiple length scales, and how device performances--although relevant for practical applications--poorly reflect the success of molecular design.
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              Amphiphilic building blocks for self-assembly: from amphiphiles to supra-amphiphiles.

              The process of self-assembly spontaneously creates well-defined structures from various chemical building blocks. Self-assembly can include different levels of complexity: it can be as simple as the dimerization of two small building blocks driven by hydrogen bonding or as complicated as a cell membrane, a remarkable supramolecular architecture created by a bilayer of phospholipids embedded with functional proteins. The study of self-assembly in simple systems provides a fundamental understanding of the driving forces and cooperativity behind these processes. Once the rules are understood, these guidelines can facilitate the research of highly complex self-assembly processes. Among the various components for self-assembly, an amphiphilic molecule, which contains both hydrophilic and hydrophobic parts, forms one of the most powerful building blocks. When amphiphiles are dispersed in water, the hydrophilic component of the amphiphile preferentially interacts with the aqueous phase while the hydrophobic portion tends to reside in the air or in the nonpolar solvent. Therefore, the amphiphiles aggregate to form different molecular assemblies based on the repelling and coordinating forces between the hydrophilic and hydrophobic parts of the component molecules and the surrounding medium. In contrast to conventional amphiphiles, supra-amphiphiles are constructed on the basis of noncovalent interactions or dynamic covalent bonds. In supra-amphiphiles, the functional groups can be attached to the amphiphiles by noncovalent synthesis, greatly speeding their construction. The building blocks for supra-amphiphiles can be either small organic molecules or polymers. Advances in the development of supra-amphiphiles will not only enrich the family of conventional amphiphiles that are based on covalent bonds but will also provide a new kind of building block for the preparation of complex self-assemblies. When polymers are used to construct supra-amphiphiles, the resulting molecules are known as superamphiphiles. This Account will focus on the use of amphiphiles and supra-amphiphiles for self-assembly at different levels of complexity. We introduce strategies for the fabrication of robust assemblies through self-assembly of amphiphiles. We describe the supramolecular approach for the molecular design of amphiphiles through the enhancement of intermolecular interaction among the amphiphiles. In addition, we describe polymerization under mild conditions to stabilize the assemblies formed by self-assembly of amphiphiles. Finally, we highlight self-assembly methods driven by noncovalent interactions or dynamic covalent bonds for the fabrication of supra-amphiphiles with various topologies. Further self-assembly of supra-amphiphiles provides new building blocks for complex structures, and the dynamic nature of the supra-amphiphiles endows the assemblies with stimuli-responsive functions.
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                Author and article information

                Journal
                Nat Chem
                Nature chemistry
                1755-4349
                1755-4330
                Aug 2014
                : 6
                : 8
                Affiliations
                [1 ] 1] National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan [2] School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire, ST55BG, UK.
                [2 ] Warsaw University of Technology, Pl. Politechniki 1, 00-661 Warsaw, Poland.
                [3 ] Laboratory of Materials and Interface Chemistry & Soft Matter CryoTEM Research Unit, Department of Chemical Engineering and Chemistry and Institute of Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
                [4 ] Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan.
                [5 ] National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan.
                [6 ] Institut Max-von-Laue-Paul-Langevin, BP 156-X, F-38042 Grenoble, Cedex, France.
                [7 ] National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan.
                [8 ] School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
                [9 ] Department of Interfaces, Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Potsdam 14476, Germany.
                [10 ] 1] National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan [2] Warsaw University of Technology, Pl. Politechniki 1, 00-661 Warsaw, Poland.
                Article
                nchem.1977
                10.1038/nchem.1977
                25054938
                d9a45e7d-11b4-49c2-b9b2-351e7878d126
                History

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