Chad A. Landis

Synthesis, Structural Characterization, and Unusual Field-Effect Behavior of Organic Transistor Semiconductor Oligomers: Inferiority of Oxadiazole Compared with Other Electron-Withdrawing Subunits

A new series of heterocyclic oligomers based on the 1,3,4-oxadiazole ring were synthesized. Other electron-deficient cores (fluorenone and fumaronitrile) were introduced to investigate the oligomers as n-channel materials. The physical properties, thin film morphologies, and field-effect transistor characteristics of the oligomers were evaluated. Thin films were deposited at different substrate temperatures and on variously coated Si/SiO(2) for device optimization. Contrary to our expectations, the thin film devices of 4 revealed p-channel behavior, and the average hole mobility was 0.14 cm(2) V(-1) s(-1) (maximum value 0.18 cm(2) V(-1) s(-1)). Compound 11 is the first example of an oxadiazole-containing organic semiconductor (OSC) oligomer in an n-channel organic field-effect transistor (OFET) and shows moderate mobilities. Non-oxadiazole-containing oligomers 9 and 12 showed n-channel OFET behavior on hexamethyldisilazane-treated and Cytop spin-coated SiO(2) in vacuum. These are the first fluorenone- and fumaronitrile-based n-OSCs demonstrated in transistors. However, oxadiazole-core materials 14 and 16 were inactive in transistor devices.

The Bergman reaction as a synthetic tool: advantages and restrictions

Abstract The Bergman cycloaromatization reaction efficiently converts easily prepared acyclic enediynes into aromatic rings. In order to prepare larger, functionalized fused aromatic systems using this reaction, a thorough understanding of how functionalization affects cycloaromatization is necessary. We present here our studies on the influence of substituents at three different functionalization sites on cycloaromatization, and how these functional groups can be tailored to prepare more complex systems.

Silylethynylated Anthracene Derivatives for use in Organic Light-Emitting Diodes

We have prepared a series of trialkylsilylethynylated anthracenes (a–d) to investigate the effects of solid-state interactions and acene substitution on the electroluminescence spectra of OLED devices. We designed these materials to have differing amounts of π-face interactions and various film morphologies. We were particularly interested in intermolecular interactions between aromatic faces, which would manifest in the electroluminescence spectrum as a bathochromic shift and broadening of the emission peak when compared to the solution photoluminescence spectrum. The anthracene derivatives with no electronic interactions, as determined by single-crystal X-ray crystallography, produced devices that showed no bathochromic shift and better efficiencies.

A new functionalization strategy for pentacene

Functionalization of the pro-cata positions of pentacene with groups held perpendicular to the aromatic plane, in this case through a rigid 1,3-dioxole unit, yields pentacene derivatives that are stable and soluble, and still maintain edge-to-face interactions in the solid state.

Synthesis, optical, thermal, and redox properties of 2,3,9,10-tetrasubstituted- 6,13- dialkynylpentacenes

A series of 2,3,9,10-tetrasubstituted-6,13-dialkynylpentacenes was synthesized and their properties evaluated. Various alkynes with different substituents were chosen to explore the effects of substitution on acene properties. The addition of alkyl groups to the pentacene 2,3,9,10-positions showed significant effects on the absorption, emission, and redox properties versus the non-alkylated (R = H) materials. The acenes exhibited excellent solubility in numerous solvents, and HOMO energy levels matched well with the work function of gold, an important electrode material. Crystallographic characterization of the methoxymethylene derivative showed it to adopt a 1-dimensional π-stacked arrangement, with good overlap of the aromatic faces.

The molecular engineering of acenes: avoiding the drawbacks of improved solubility [organic electronics materials]

Acenes such as anthracene, tetracene and pentacene are high-performance components of several classes of organic devices. Significant research has been aimed at making these normally insoluble materials into compounds that can be processed by solution methods. We report our approach to acene solubilization by careful consideration of how substituents affect the solid-state order of the materials. This change in native order leads to increases in conductivity, and in collaboration with the Jackson group has shown TFT mobilities >0.5 cm/sup 2//Vs from both vapor and solution. With this initial data in hand, we report our progress on second-generation materials designed to address the shortcomings of our initial compounds.

Cycloaromatization approach to planar and cylindrical carbon oligomers

Cycloaromatization chemistry has the potential to become an important paradigm for the formation of graphitic oligomers. We will explore various motifs of cycloaromatization, and demonstrate their usefulness to the preparation of fused aromatic systems.