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Daron E Janzen

Publications and source records attributed to Daron E Janzen.

10 recordsLinked to original sources
PubMed2006

Exploration of ground and excited electronic states of aromatic and quinoid S,S-dioxide terthiophenes. Complementary systems for enhanced electronic organic materials.

We analyze 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). These represent extremes of electron rich and deficient ground states, often exhibiting complementary properties. Oxidizing the central sulfur atom affects the molecular structure, electron affinity, and photophysical properties of both pi systems. The consequences for 3T include de-aromatization of the central thiophene, red-shifting of the electronic absorption spectrum, and lowering of the reduction potential. The electron deficient quinoid 3QO2 shows an enhancement of electron affinity from reducing the electron-donor ability of sulfur, and a blue-shifting of its electronic absorption spectrum was seen. Fluorescence emission is quenched in the sulfonated terthiophene, and the contrary effect again would be expected upon sulfonation of a quinoid emitter. Raman vibrational spectroscopy, electrochemistry, and UV-vis and fluorescence spectroscopies are analyzed in conjunction with theoretical calculations.

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PubMed2006

Optical, redox, and NLO properties of tricyanovinyl oligothiophenes: comparisons between symmetric and asymmetric substitution patterns.

A series of tricyanovinyl (TCV)-substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X-ray diffraction, and cyclic voltammetry. Mono- or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono- or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X-ray structural characterization of a monosubstituted oligomer exhibits pi-stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge-transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs).

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PubMed2005

Cationic five-coordinate Pt(II) complexes as donors in the formation of Pt-->Ag dative bonds.

A unique trinuclear cluster containing two short Pt-->Ag dative bonds was prepared and characterized crystallographically. Two monocationic orthometalated Pt(II) complexes containing 2-phenylpyridine and the tridentate ligand 9S3 (1,4,7-trithiacyclononane) exhibit axial sulfur interactions with Pt as well as short dative bonds. The Pt-->Ag dative bonding results in a dramatic shortening of the axial Pt-S distance in each Pt complex cation, relative to the mononuclear Pt complex. Evidence for Pt-Ag interactions in solution is also presented.

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PubMed2005

1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane diiodide acetonitrile solvate.

In the crystal structure of the title compound, C(8)H(18)N(2)(2+).2I(-).CH(3)CN, 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) A. The dications pack forming channels along the b axis, which contain the iodide anions and acetonitrile solvent molecules.

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PubMed2004

Preparation and characterization of pi-stacking quinodimethane oligothiophenes. Predicting semiconductor behavior and bandwidths from crystal structures and molecular orbital calculations.

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 (epsilon congruent with 100 000 M(-1) cm(-1)) low energy pi-pi transition that has a lambda(max) ranging between 648 and 790 nm. All X-ray crystal structures exhibit very planar quinoidal backbones and short intermolecular pi-stacking distances (3.335-3.492 A). Structures exhibit a single pi-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 pi-stacking. For structures with a unique pi-stacking distance, a simple geometric overlap parameter calculated from the shape of the molecule and the slip from perfect registry in the pi-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.

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PubMed2004

Triethylammonium tetraphenylborate dichloromethane solvate.

The crystal structure of the title compound, C6H16N+.C24H20B-.CH2Cl2, displays an N-H...pi interaction between the triethylammonium cation and a phenyl ring of the tetraphenylborate anion. The distance between the ammonium H atom and the edge of this phenyl ring is 2.40 (3) A. The ammonium group and the aryl moiety are nearly perpendicular, forming an intramolecular dihedral angle of 90.4 degrees. A C-H...pi interaction between the disordered dichloromethane solvate molecule and a phenyl ring of the tetraphenylborate anion is also present.

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PubMed2003

Synthesis and characterization of tricyanovinyl-capped oligothiophenes as low-band-gap organic materials.

Tricyanovinyl-capped oligothiophenes of up to six rings have been synthesized and characterized. The substituted oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison to unsubstituted oligomers. The solvatochromic behavior of the terthiophene-substituted molecule was investigated in a variety of solvents. Stable oxidations and reductions were exhibited by the sexithiophene-substituted molecule on the CV time scale. [structure: see text]

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PubMed2002

Ligand substitution, pH dependent deoxygenation, and linkage isomerization reactions of the 2,2'-bipyridinetetranitroruthenate dianion.

The reaction of the [Ru(bpy)(NO(2))(4)](2-) (bpy = 2,2'-bipyridine) ion in aqueous solutions produces two different nitrosyl complexes, depending on the pH of the solution. At acidic pH, complex cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was isolated. At neutral or basic pH, [Ru(bpy)(NO(2))(4)](2-) reacts to give cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH). Both new complexes were fully characterized by elemental analysis and UV-vis, IR, (1)H NMR, and (15)N NMR spectroscopy. A single-crystal X-ray structure of cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH) was also obtained. cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) isomerizes in acetone or water solution to give a mixture of the trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) and cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO) linkage isomers as determined by (1)H and (15)N NMR spectroscopy. A single-crystal X-ray structure of a solid solution of cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO)/trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was also obtained. This pair of isomers is the first crystallographically characterized compound with nitro, nitrito, and nitrosyl ligands. The kinetic studies of the Ru-NO(2) --> Ru-NO conversion reactions of [Ru(bpy)(NO(2))(4)](2)(-) in buffered solutions from pH 3 to pH 9 complement previous studies of the reverse reaction. The reactions are first order in [Ru(bpy)(NO(2))(4)](2-). At high pH, the reaction is independent of the concentration of H(+) while, at low pH, the reaction is first order in the concentration of H(+). The rate determining step of the high pH reaction involves breakage of the Ru-NO(2) bond while, at low pH, the mechanism involves a rapid reversible protonation of a NO(2) ligand followed by the rate determining loss of hydroxide to produce a nitrosyl ligand.

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PubMed2002

Characterization of a cross-reactive electronic nose with vapoluminescent array elements.

A three-channel cross-reactive sensor array based on vapoluminescent platinum(II) double salt materials has been characterized. Two arrays were studied, one consisting of [Pt(CN-cyclododecyl)4][Pt(CN)4] (1), [(phen)Pt(CN-cyclohexyl)2][Pt(CN)4] (2), and [Pt(CN-n-tetradecyl)4][Pt-(CN)4] (3) materials, where phen = 1,10-phenanthroline, and a second array that has compound 3 replaced by the mixed double salt material [(phen)Pt(CN-cyclododecyl)Cl)]2[(phen)Pt(CN-cyclododecyl)2]2[Pt(CN)4]3 (4). Compounds 2, 3 and 4 are characterized here for the first time. Inclusion of solvent vapors into these materials often leads to dramatic shifts in their solid-state absorption and luminescence spectra. In these studies the arrays were exposed to a set of 10 test solvent vapors to determine the ability of each cross-reactive array to give reproducible vapoluminescent spectra characteristic of each solvent vapor. It was discovered that temperature programming between solvent vapor exposures greatly improved the reproducibility of the luminescence spectra obtained. A statistical analysis of three-dimensional resolution factors between pairs of solvent clusters in principal component space supported this assertion. The success of the temperature programming protocol was limited by the thermal stability and the sensitivity to low background water vapor levels of some platinum(II) double salt materials. The ability of the cross-reactive sensor array to differentiate between two different solvent vapors over a large concentration range was also investigated. Acetone and methanol were found to occupy two distinct regions of the three-dimensional principal component space. Detection limits for acetone and methanol were estimated from the principal component analysis as 75 and 6 g/m3, respectively.

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