Polymer-sorted semiconducting carbon nanotube networks for high-performance ambipolar field-effect transistors.

Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm(2)·V(-1)·s(-1), low ohmic contact resistance, steep subthreshold swings (0.12-0.14 V/dec) and high on/off ratios (10(6)) even for short channel lengths (<10 µm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61.

Carbon nanotube network ambipolar field-effect transistors with 10(8) on/off ratio.

Polymer wrapping is a highly effective method of selecting semiconducting carbon nanotubes and dispersing them in solution. Semi-aligned semiconducting carbon nanotube networks are obtained by blade coating, an effective and scalable process. The field-effect transistor (FET) performance can be tuned by the choice of wrapping polymer, and the polymer concentration modifies the FET transport characteristics, leading to a record on/off ratio of 10(8) .

trans-thionate derivatives of Pt(II) and Pd(II) with water-soluble phosphane PTA and DAPTA ligands: antiproliferative activity against human ovarian cancer cell lines.

A series of PTA and DAPTA platinum(II) and palladium(II) thionate complexes of the type trans-[M(SN)2P2] were prepared from the reaction of cis-[MCl2P2] [M = Pt, Pd; P = PTA (1,3,5-triaza-7-phosphaadamantane), DAPTA (3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane)] with the in situ generated sodium salts of the heterocyclic thiones S-m-methylpyrimidine-2-thione, S-4,6-dimethylpyrimidine-2-thione, S-4,6-dihydroxypyrimidine-2-thione, benzothiazole-2-thione, benzoxazole-2-thione, S-1,3,4,-thiadiazole-2-thione, S-4,5-H-thiazolan-2-thione, and S-pyrimidine-4(1H)-one-2-thione. The X-ray structures of six of the compounds confirm the trans disposition and, only in the case of [Pd2Cl2(S-pyrimidine-4(1H)-one-2-thionate)2(PTA)2], a dinuclear structure with a Pd-Pd distance of 3.0265(14)Å was observed. In vitro cytotoxicities against human ovarian cancer cell lines A2780 and A2780cisR were evaluated for ten complexes showing a high inhibition of cellular growth with a comparable inhibitory potency (IC50) against A2780 cells to that of cisplatin. Notably, the compounds also show significant (up to 7-fold higher) activity in cisplatin-resistant A2780cisR cell lines.

Semiconducting single-walled carbon nanotubes on demand by polymer wrapping.

Efficient selection of semiconducting SWCNTs of large diameter range (0.8-1.6 nm) on demand is demonstrated. Different diameters of SWCNT are systematically selected by tuning the alkyl side-chain lengths of the wrapping polymers of similar backbone. The exceptional quality and high concentration of the SWCNTs is validated by the outstanding optical properties and the highly performing random network ambipolar field-effect transistors.

Charge photogeneration in donor-acceptor conjugated materials: influence of excess excitation energy and chain length.

We investigate the role of excess excitation energy on the nature of photoexcitations in donor-acceptor π-conjugated materials. We compare the polymer poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[1,2-b;3,4-b']dithiophene)-4,7-benzo[2,1,3]thiadiazole) (PCPDTBT) and a short oligomer with identical constituents at different excitation wavelengths, from the near-infrared up to the ultraviolet spectral region. Ultrafast spectroscopic measurements clearly show an increased polaron pair yield for higher excess energies directly after photoexcitation when compared to the exciton population. This effect, already observable in the polymer, is even more pronounced for the shorter oligomer. Supported by quantum chemical simulations, we show that excitation in high-energy states generates electron and hole wave functions with reduced overlap, which likely act as precursors for the polaron pairs. Interestingly, in the oligomer we observe a lifetime of polaron pairs which is one order of magnitude longer. We suggest that this behavior results from the intermolecular nature of polaron pairs in oligomers. The study excludes the presence of carrier multiplication in these materials and highlights new aspects in the photophysics of donor-acceptor small molecules when compared to polymers. The former are identified as promising materials for efficient organic photovoltaics.