Line-on-line organic-organic heteroepitaxy of quaterrylene on hexa-peri-hexabenzocoronene on Au(111)

In a recent paper, we discussed the optical properties of a heterostructure consisting of a highly ordered monolayer of quaterrylene (QT), electronically decoupled from the gold substrate by a predeposited epitaxial monolayer of hexa-peri-hexabenzocoronene (HBC). Here we now present the detailed structural investigation of this organic double-layer system. We show that the structure of the heterosystem can be identified as line-on-line coincidence (lol), a new type of epitaxy discovered by us previously for the system 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on HBC on highly oriented pyrolytic graphite (HOPG). Additionally, we provide evidence on the basis of advanced potential energy calculations that indeed energetic gain drives this lol growth mode.

One-pot preparation of dendrimer-gold nanoparticle hybrids in a dipolar aprotic solvent

We present a simple one-pot, one-step method to obtain stable and nearly monodisperse gold nanoparticles in dipolar aprotic solvents. Novel thiomethyl-functionalized polyphenylene dendrimers are used to control the growth and stabilize the nanoparticles in suspension. The dendrimer functionalized gold nanoparticles have an average size of roughly 10 nm and are stable in suspension for several weeks. The stability in dipolar aprotic solvents and the great functionalization flexibility offered by the dendrimers make these metal/dendrimer hybrid systems promising for applications such as nanophotonics, molecular electronics, and sensing.

Transparent, highly conductive graphene electrodes from acetylene-assisted thermolysis of graphite oxide sheets and nanographene molecules

Transparent and highly conductive graphene electrodes have been fabricated through acetylene-assisted thermolysis of graphite oxide (GO) sheets. This novel procedure uses acetylene as a supplemental carbon source to repair substantial defects within GO sheets, leading to the enhancement of graphitization of synthesized graphene electrodes. The as-prepared graphene on quartz substrates exhibits an electrical conductivity of 1425 S cm(-1) with an optical transmittance of more than 70% at a wavelength of 500 nm. Such an acetylene-assisted thermal treatment approach is also adopted to fabricate graphene electrodes from synthetic nanographene molecules, with an almost five times increase in conductivity compared to samples prepared by the common thermal reduction.

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.

Control of the electronic energy transfer pathway between two single fluorophores by dual pulse excitation

We report on the control of the energy transfer pathway in individual donor-acceptor dyads by proper timing of light pulses matching the donor and acceptor transition frequencies, respectively. Excitation of both chromophores at virtually the same time induces efficient singlet-singlet annihilation, whereby excitation energy effectively flows from the acceptor to the donor. The dual pulse excitation scheme implemented here allows for all-optical switching of the fluorescence intensity at the single-molecule level. The population of higher excited states at the donor site was found to significantly increase the photobleaching probability.

Catalyst-free preparation of melamine-based microporous polymer networks through Schiff base chemistry

Recently, the synthesis of organic materials with high porosity has received considerable scientific interest, and various chemical approaches have been applied to the build-up of microporous polymer networks. In a novel catalyst-free process using Schiff base chemistry, melamine has been reacted with various di- and trivalent aldehydes to form a series of highly cross-linked microporous aminal networks with BET surface areas as high as 1377 m(2)/g and a NLDFT micropore volume of up to 0.41 cm(3)/g. It was shown that through the proper choice of the starting compounds the porosity of the final material can be fine-tuned. The materials contain up to 40 wt % of nitrogen and were also found to exhibit high thermal stability. Owing to the cheap and abundant monomers used in this study these networks are promising candidates for large-scale applications in gas storage, gas separation, catalysis, and sensing.

Tailoring structure-property relationships in dithienosilole-benzothiadiazole donor-acceptor copolymers

Four new DTS-BTD copolymers (P1-P4) differing by the concentration of electron-donating and -withdrawing substituents along the backbone have been synthesized and characterized by 2D-WAXS and in bottom-contact FETs. While all copolymers can self-assemble into lamellar superstructures, only P2 and P4 show a propensity to pi-stack. P4 exhibits a hole mobility as high as 0.02 cm(2) V(-1) s(-1) in excellent agreement with the close pi-stacking and lamellar distances found by structural analysis (0.36 and 1.84 nm, respectively) and absorbs homogenously across the entire visible spectrum as solar cell applications require.