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We report structural and electrical properties in thin films of an n-channel organic semiconductor, N,N′-dipentyl-3,4,9,10-perylene tetracarboxylic dimide (PTCDI–C5). The structure of polycrystalline thin films of PTCDI–C5 was studied using x-ray diffraction and atomic force microscopy. Films order with single crystal-like packing, and the direction of π-π overlap is in the substrate plane. Organic thin film transistors (OTFTs) based on PTCDI–C5 were fabricated on hydrophobic and hydrophilic substrates. OTFTs showed effective mobility as high as 0.1 cm2/V s. Contact resistance of operating OTFTs was studied using resistance versus length plots and a four-probe method for three different contact metals (Au, Ag, Ca). Typical OTFTs had a specific contact resistance of 8×104 Ω cm at high gate voltage. There was no dependence of contact resistance with contact metal. Variable temperature measurements revealed that film resistance in the OTFT was activated in the temperature range 100–300 K, with typical activation energies of 60–80 meV. Contact resistance showed similar activated behavior, implying that the Schottky barrier at the contact is not the limiting resistance for the contact. Film resistance data showed a Meyer–Neldel relationship with characteristic energy EMN=20–25 meV, for various samples. The common TFT instability of threshold voltage shift (TVS) was observed in PTCDI–C5 OTFTs. A model is proposed to explain positive TVS in gate bias stress and oxygen exposure experiments. The model is based on the formation of a metastable complex between PTCDI–C5 and oxygen, which creates a deep acceptor-like trap state. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronic and molecular structures for the ground and excited electronic states of aromatic terthiophene (3T), the quinodimethane 3',4'-dibutyl-5,5'-bis(dicyanomethylene)-5,5'-dihydro-2,2':5',2'-terthiophene (3Q), and isologues with the middle ring S-oxidized (3TO2, 3QO2) are analyzed. These have represented the extremes of electron rich and deficient ground states, often displaying complementary properties and the florescence emission is quenched in the sulfonated terthiophene and the contrary effect again would be expected upon sulfonation of a quinoid emitter.

Ammonolysis of RGa(NMe2)2]2 led to microcrystalline powders having the general formula of [RGaNH]n. X-ray powder diffraction and crystal structure modeling established that stacks of six-membered [RGaNH]3 rings connected through axial Ga-N bonds comprised the rod cores, which were coated with a hydrocarbon shell.

Structural and electrical transport properties of a family of pi-stacking soluble organic semiconductors, N,N'-dialkyl-3,4,9,10-perylene tetracarboxylic diimides is reported. Further, the structures of evaporated polycrystalline films are studied using X-ray diffraction and atomic force microscopy.

The synthesis and characterization of quinodimethane-substituted oligomers is reported. The electrochemistry of these materials indicates their suitability for both p and n biasing in field effect transistors (FETs).

In the crystal structure of the title compound, C8H18N22+·2I−·CH3CN, the dication lies on a mirror plane containing the mol­ecular dication threefold axis. The structure displays C—H⋯I inter­actions between H atoms of the 1,4-dimethyl-1,4-diazo­nia­bicyclo­[2.2.2]octane dication and the iodide anions. The H⋯I distances are in the range 2.96–3.18 (4) Å. The dications pack forming channels along the b axis, which contain the iodide anions and acetonitrile solvent mol­ecules. [ABSTRACT FROM AUTHOR]

A series of new quinodimethane-substituted terthiophene and quaterthiophene oligomers has been investigated for comparison with a previously studied quinoid oligothiophene that has demonstrated high mobilities and ambipolar transport behavior in thin-film transistor devices. Each new quinoidal thiophene derivative shows a reversible one-electron oxidation between 0.85 and 1.32 V, a quasi-reversible one-electron second oxidation between 1.37 and 1.96 V, and a reversible two-electron reduction between -0.05 and -0.23 V. The solution UV-vis-NIR spectrum of each compound is dominated by an intense (∊ ≅ 100000 M-1 cm-1) low energy π-π* transition that has a λmax ranging between 648 and 790 nm. All X-ray crystal structures exhibit very planar quinoidal backbones and short intermolecular π-stacking distances (3.335-3.492 Å). Structures exhibit a single 21-stacking distance with parallel cofacial stacking (sulfur atoms of equivalent rings pointed in the same direction) or with alternating distances and antiparallel cofacial stacking (sulfur atoms of equivalent rings pointed in the opposite direction). Examples of the layered and herringbone-packing motifs are observed for both the parallel and the antiparallel cofacial stacking. Analysis of the X-ray structures and molecular orbital calculations indicates that all of these compounds have one-dimensional electronic band structures as a result of the π-stacking. For structures with a unique π-stacking distance, a simple geometric overlap parameter calculated from the shape of the molecule and the slip from perfect registry in the π-stack correlates well with the transfer integrals (t) calculated using molecular orbital theory. The calculated valence (633 meV) and conduction (834 meV) bandwidths for a quinoid quaterthiophene structure are similar to those calculated for the benchmark pentacene and indicate that both hole and electron mobilities could be significant. [ABSTRACT FROM AUTHOR]

Oligothiophene sulfones of up to six rings can be conveniently prepared by the direct oxidation of butyl-substituted thiophene oligomers with m-CPBA in dichloromethane. Reverse selectivity of oxidized rings is observed relative to previously reported systems without beta-substitution. The selectivity in the trimer and hexamer is confirmed with single-crystal X-ray structure data. The sulfones possess red-shifted absorptions and increased electron affinities relative to the parent oligomers.

The synthesis and self-assembly of twelve semifluorinated first-generation dendrons or minidendrons attached to electron-acceptor (n-type) groups generated from various combinations of eight acceptors and three dendrons are reported. Dendrons attached to small electron-acceptor molecules mediate their self-assembly into pi-stacks located in the center of a supramolecular helical pyramidal column with the long axis of the acceptor perpendicular to the long axis of the column. Dendrons attached to large electron-acceptor molecules, such as perylene bisimide, mediate the assembly of their acceptors in an unprecedented arrangement of pi-stacks that have the long axis of the acceptors parallel to the long axis of the supramolecular pyramidal column. All supramolecular columns self-organize into various periodic columnar arrays that exhibit liquid-crystalline phases, crystalline phases, or a liquid-crystalline phase with enhanced intracolumnar order. The present study demonstrates the simplicity and the versatility of the concept of assembly of n-type electroactive groups mediated by semifluorinated dendrons and assesses the scope and limitations of this supramolecular strategy.