Bridging of gold nanoparticles by functional polyphenylene dendrimers.

We describe a protocol for the in-suspension bridging of gold particles with shape-persistent polyphenylene dendrimers, carrying multiple lipoic acid groups at their periphery. A solvent mixture is identified where both reactants are stable as individuals. Upon mixing, aggregates with stoichiometry-dictated size form rapidly. Initially, the spacing between individual gold colloids is large enough that their absorption spectrum is only slightly different from isolated particles. The aggregates rearrange within hours, leading to strong optical coupling between the gold particles and a corresponding spectral shift.

Electron-deficient N-heteroaromatic linkers for the elaboration of large, soluble polycyclic aromatic hydrocarbons and their use in the synthesis of some very large transition metal complexes.

The selective oxidation of the perimeter of an extended polycyclic aromatic hydrocarbon (PAH), namely a six-fold tert-butylated tetrabenzo[bc,ef,hi,uv]ovalene, led to the formation of an alpha-diketone. The newly installed carbonyl centers allowed this building block to be converted into the largest known heteroatom-containing PAHs (up to 224 atoms in the aromatic core) by way of the quinoxaline ring condensation reaction. The tert-butyl substituents caused a distortion of the usually planar aromatic frameworks, which hampered the aggregation tendency of the extended aromatic pi-systems and led to extraordinarily high solubilities. All of the systems described here, even the giant phthalocyanine, could thus be purified using standard chromatographic techniques and characterized using typical spectroscopic methods. For the first time, fully resolved 1H NMR spectra of soluble, diamagnetic, 98- and 104-atom-containing aromatic systems are presented. The computed and experimental UV/vis spectra emphasize the dependence of the characteristic alpha-, p-, and beta-bands upon the size of the PAHs. It was also possible to obtain the largest known ligand to yet be complexed around a ruthenium center. A quadrupolar solvatochromic effect was observed when two donating PAH moieties were fused to an accepting quinoxaline center, in which case the photoluminescence spanned a range of about 80 nm. Electrochemical properties of the new nanographenes were investigated using cyclic voltammetry, and this showed quasi-reversible reductions.

Suppressing aggregation in a large polycyclic aromatic hydrocarbon.

With the approach presented herein, a large aromatic pi-system is synthesized, which shows extraordinarily high solubility and an effective suppression of aggregation. This was due to a distortion of the aromatic core by bulky tert-butyl groups and the solubilizing effects of alkyl chains in the corona of the aromatic core. Therefore not only the processing and cleaning of the materials with standard laboratory techniques became possible, but moreover the first structure-rich UV/vis and a resolved (1)H NMR spectra for an aromatic system two times larger than hexa-peri-hexabenzocoronene were recorded. The bulk properties in an extruded fiber as well as on the surface showed a columnar self-assembly including a phase in which a homeotropic alignment on a substrate was observed, which turns the material into an interesting candidate for future applications in electronic devices.