Highly Selective Dispersion of Single-Walled Carbon Nanotubes via Polymer Wrapping: A Combinatorial Study via Modular Conjugation.

Fourteen different "hairy-rod" conjugated polymers, 9,9-dioctylfluorene derivatives entailing 1,2,3-triazole, azomethine, ethynyle, biphenyle, stilbene, and azobenzene lateral units, are synthesized via modular conjugation and are systematically investigated with respect to their ability to selectively disperse SWCNTs. Four polymers of the azomethine type, with unprecedented selectivity toward dispersing (8,7), (7,6), and (9,5) SWCNT species, have been identified. In particular, azomethine polymers, herein applied for the first time for SWCNT dispersion, have been evidenced to be very effective in the highly selective solubilization of SWCNTs. The experimentally observed selectivity results are unambiguously supported by molecular dynamics simulations that account for the geometrical properties and deformation energy landscape of the polymer. Specifically, the calculations accurately and with high precision predict the experimentally observed selectivity for the (7,6) and (9,5) conformations.

RAFT mediated polymerization of methyl methacrylate initiated by Bergman cyclization: access to high molecular weight narrow polydispersity polymers.

The first RAFT mediated polymerization of methyl methacrylate initiated by diradicals derived from Bergman cyclization was performed employing 3,4-benzocyclodec-3-ene-1,5-diyne (BCDY) as diradical source and cyanoisopropyldithiobenzoate (CPDB) as RAFT agent. The polymerization was conducted in bulk at 80 °C for 3 h. The concentration of the enediyne was kept constant at 3.0 x 10⁻² mol · L⁻¹ and the RAFT agent concentration was varied between 0.0 mol · L⁻¹ and 2.4 x 10⁻¹ mol · L⁻¹. A detailed ESI-MS analysis reveals the absence of intramolecular termination reactions (ring formation) in the RAFT mediated system, which usually makes diradicalic initiation unfavorable. The presence of polymeric chains propagating at both ends could be confirmed. The conversion of the RAFT mediated polymerization was up to more than two times higher than the RAFT free polymerization at identical conditions. Thus, polymers with narrow polydispersities (1.1 ≤ PDI ≤ 1.5) even at very high molecular weights (near 400,000 Da) were obtained within modest reaction times.

Selective dispersion of single-walled carbon nanotubes with specific chiral indices by poly(N-decyl-2,7-carbazole).

Physico-chemical methods to sort single-walled carbon nanotubes (SWNTs) by chiral index are presently lacking but are required for in-depth experimental analysis and also for potential future applications of specific species. Here we report the unexpected selectivity of poly(N-decyl-2,7-carbazole) to almost exclusively disperse semiconducting SWNTs with differences of their chiral indices (n - m) ≥ 2 in toluene. The observed selectivity complements perfectly the dispersing features of the fluorene analogue poly(9,9-dialkyl-2,7-fluorene), which disperses semiconducting SWNTs with (n - m) ≤ 2 in toluene. The dispersed samples are further purified by density gradient centrifugation and analyzed by photoluminescence excitation spectroscopy. All-atom molecular modeling with decamer model compounds of the polymers and (10,2) and (7,6) SWNTs suggests differences in the π-π stacking interaction as origin of the selectivity. We observe energetically favored complexes between the (10,2) SWNT and the carbazole decamer and between the (7,6) SWNT and the fluorene decamer, respectively. These findings demonstrate that subtle structural changes of polymers lead to selective solvation of different families of carbon nanotubes. Furthermore, chemical screening of closely related polymers may pave the way toward simple, low-cost, and index-specific isolation of SWNTs.

Single chain self-assembly: preparation of alpha,omega-donor-acceptor chains via living radical polymerization and orthogonal conjugation.

Alpha,omega-hydrogen donor/acceptor functional polymer strands are prepared via a combination of living radical polymerization and orthogonal conjugation and subsequently self-assembled as single chains to emulate--on a simple level--the self-folding behaviour of natural biomacromolecules.

Templated self-assembly of ZnO films on monolayer patterns with nanoscale resolution.

Lithographically defined self-growing ZnO films were prepared by a bioinspired chemical bath deposition technique (CBD). We observed a high selectivity of ZnO deposition: Teflon-like per-fluoro-decyl-trichlorosilane (FDTS) monolayers repelled ZnO primary particles, whereas amino-functionalized areas of the substrate were selectively covered by a highly anisotropic, oriented, and compact ZnO film with a thickness of 50 nm. The size of the primary particles in our methanol-based solution was approximately 2.5 nm. On the amino substrate they formed agglomerates not larger than 30 nm. Monolayer patterns made by polymer blend lithography were templated with an edge resolution of 30 nm. By using a specialized derivative of microcontact printing, we prepared layout-defined silane templates, which reliably determined the growth of a layout-defined, patterned oxide film with submicrometer lateral resolution.

DNA-templated synthesis of ZnO thin layers and nanowires.

In this paper, we report a novel synthetic approach towards electrically conductive ZnO nanowires close to ambient conditions using lambda-DNA as a template. Initially, the suitability of DNA to assemble ZnO nanocrystals into thin coatings was investigated. The ZnO nanowires formed on stretched and aligned lambda-DNA molecules were prepared via chemical bath deposition (CBD) of zinc acetate in methanol solution in the presence of polyvinylpyrrolidone (PVP). After 10 deposition cycles, the nanowires exceed 10 microm in length and the height can be varied from 12 to around 40 nm. The nanocrystalline structure of the ZnO wires was confirmed by high-resolution transmission electron microscopy (HRTEM). The electrical conductivity was found to be of the order of several Omega cm at room temperature in two terminal measurements.