Electrical properties of nanofibers and structural characterization of DNA-Au(III) complexes.

In order to realize deoxyribonucleic acid (DNA)-based molecular electronics, chemical modifications of DNA are needed to improve electrical conductivity. We developed a novel method utilizing the incorporation of Au(III) ions into DNA bases to alter their electronic properties. When Au(III) ions were incorporated proportionally into DNA bases, conductance increased up to an Au(III) content of 0.42 Au(III) ion/nucleotide. Surprisingly, electron paramagnetic resonance signals of Au(II) ions were detected at g ∼1.98, and the calculated spin number of Au(II) ions ranged from ∼10(13) to ∼10(15). The structural deformation of the DNA helix occurred when complexed with Au(III); simultaneously, the conductance of DNA-Au(III) complexes decreased when the content of Au(III) was higher than 0.42 atom/nucleotide. This observation implies that the maintenance of helical structure in the Au(III) doped state of DNA molecules is very important to the enhancement of the carrier mobility of DNA.

J-aggregation induced low bandgap anthracene-based conjugated molecule for solution-processed solar cells.

A new anthracene-based X-shaped conjugated molecule, HBTATHT, was synthesized. Thin film transistors based on unannealed HBTATHT showed a carrier mobility of 0.15 cm(2) V(-1) s(-1) (I(on/off) = 7.9 × 10(6)). Further, a solution processed solar cell made of HBTATHT exhibited promising power conversion efficiencies of 4.84% and 4.70% with PC(61)BM (1:0.8 wt ratio) and PC(71)BM (1:0.6 wt ratio), respectively.

DNA-templated preparation of gold nanoparticles.

DNA-mediated gold nanoparticles were prepared by chemical reduction of DNA-Au(III) complex. The DNA-Au(III) was first formed by reacting DNA with HAuCl4 at a pH of 5.6. The complex in solution was reacted with hydrazine reducing Au(III) to Au. The reduced Au formed nanodimensional aggregates. The particle distributions were obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This method resulted in a rather uniform dispersion of Au nanoparticles of near-spherical shape and 45~80 nm in diameter. Gold nanoparticles were embedded and stabilized by DNA.

High-temperature ferromagnetism of a discotic liquid crystal dilutely intercalated with iron(III) phthalocyanine.

Room-temperature ferromagnetism of an organic discotic liquid crystalline compound (DLC) is achieved by intercalation at low levels with paramagnetic iron(III) phthalocyanine (see figure). These ferromagnetic DLCs are very similar to the so-called dilute magnetic semiconductors of inorganic nature. It is expected that this novel approach will open up a new way of preparing the high-temperature organic ferromagnetic compounds needed for molecular spintronics.

Role of Au nanoparticles in efficiency enhancement and green band emission quenching of blue polymer light emitting diodes.

We studied photoluminescence (PL) and electroluminescence (EL) properties of polymer light emitting diodes (PLEDs) constructed with polyconjugated polymers blends containing Au nanoparticles (DA-Au NPs; 5.3 nm +/- 1.1 nm in diameter) capped by dodecylamine. For the blue light emitting polyfluorene polymers, selective quenching of excimer peaks or so-called green bands was observed in PL as well as in EL when they were mixed with small amounts (1-4 wt%) of DA-Au NP. The influence of DA-Au NPs on the light-emitting characteristics of the PLEDs strongly depended on the nature of the matrix polymer, which was particularly conspicuous for the polymers whose emission wavelength matches or overlaps with the surface plasmon resonance wavelength region of Au nanoparticles. Especially, the purity of the blue color emitted by the poly [2,7-(9,9-di-n-dioctylfluorene) (PF) was greatly improved by Au NPs that suppressed the 'green band.' All the PLEDs doped with DA-Au NPs showed enhanced maximum external quantum efficiency and emitted light intensity when compared to undoped counterparts.

Formation of gold nanoparticles within a liquid crystalline polymeric matrix.

We could prepare a novel composite consisting of a liquid crystalline polyester matrix and gold nanoparticles (7-14 nm). The polymer bears methoxy-terminated, hydrophilic, low molecular weight (350) PEG pendants on the rigid, hydrophobic aromatic polyester backbone. The polymers from a layered, sematic-like morphology at room temperature, where the interlayer is occupied by the PEG pendants. An aqueous solution of HAuCl4 was allowed to diffuse into the hydrophilic domains and the gold ions were reduced by hydrazine to gold nanoparticles. Our findings combine the concepts of self-assembly and nanoparticles, which can lead to formation of many interesting new nanocomposites.