4 research outputs found
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<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>, low ohmic contact resistance,
steep subthreshold swings (0.12–0.14 V/dec) and high on/off
ratios (10<sup>6</sup>) 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
<i>trans</i>-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 <i>trans</i>-[M(SN)<sub>2</sub>P<sub>2</sub>] were prepared from the reaction of <i>cis</i>-[MCl<sub>2</sub>P<sub>2</sub>] [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 <i>in situ</i> generated sodium salts of the heterocyclic
thiones <i>S</i>-<i>m</i>-methylpyrimidine-2-thione, <i>S</i>-4,6-dimethylpyrimidine-2-thione, <i>S</i>-4,6-dihydroxypyrimidine-2-thione,
benzothiazole-2-thione, benzoxazole-2-thione, <i>S</i>-1,3,4,-thiadiazole-2-thione, <i>S</i>-4,5-<i>H</i>-thiazolan-2-thione, and <i>S</i>-pyrimidine-4(1<i>H</i>)-one-2-thione. The X-ray
structures of six of the compounds confirm the <i>trans</i> disposition and, only in the case of [Pd<sub>2</sub>Cl<sub>2</sub>(<i>S</i>-pyrimidine-4(1<i>H</i>)-one-2-thionate)<sub>2</sub>(PTA)<sub>2</sub>], a dinuclear structure with a Pd–Pd
distance of 3.0265(14)Å was observed. <i>In vitro</i> 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 (IC<sub>50</sub>) 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
<i>trans</i>-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 <i>trans</i>-[M(SN)<sub>2</sub>P<sub>2</sub>] were prepared from the reaction of <i>cis</i>-[MCl<sub>2</sub>P<sub>2</sub>] [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 <i>in situ</i> generated sodium salts of the heterocyclic
thiones <i>S</i>-<i>m</i>-methylpyrimidine-2-thione, <i>S</i>-4,6-dimethylpyrimidine-2-thione, <i>S</i>-4,6-dihydroxypyrimidine-2-thione,
benzothiazole-2-thione, benzoxazole-2-thione, <i>S</i>-1,3,4,-thiadiazole-2-thione, <i>S</i>-4,5-<i>H</i>-thiazolan-2-thione, and <i>S</i>-pyrimidine-4(1<i>H</i>)-one-2-thione. The X-ray
structures of six of the compounds confirm the <i>trans</i> disposition and, only in the case of [Pd<sub>2</sub>Cl<sub>2</sub>(<i>S</i>-pyrimidine-4(1<i>H</i>)-one-2-thionate)<sub>2</sub>(PTA)<sub>2</sub>], a dinuclear structure with a Pd–Pd
distance of 3.0265(14)Å was observed. <i>In vitro</i> 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 (IC<sub>50</sub>) 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
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-<i>b</i>;3,4-<i>b</i>′]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