Ted M. Pappenfus

Complexes of Lithium Imide Salts with Tetraglyme and Their Polyelectrolyte Composite Materials

Complexes of amorphous tetraglyme (G4) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or lithium bis(perfluoroethyl-sulfonyl)imide (LiBETI) were prepared as pol(yethylene) oxide-type electrolytes. Addition of equimolar amounts of LiTFSI and tetraglyme results in a room temperature ionic liquid with the general formula [Li(G4)]TFSI. Differential scanning calorimetry analysis of [Li(G4)]TFSI reveals that it has a T g = -61°C, and the complex remains amorphous over a wide temperature range (-100 to 200°C), and has a very low vapor pressure for tetraglyme at room temperature. The corresponding BETI complex, [Li(G4)]BETI, crystallizes upon cooling and displays a T m = 31°C. Room temperature conductivities (25°C) of [LilG4)]TFSI and [Li(G4)]BETI were 1.13 and 0.63 mS/cm, respectively. Composite polymer electrolytes were prepared by addition of the complexes to polycations possessing TFSI or BETI anions. The composites afforded thin flexible membranes at polymer concentrations ≥50 mol % polymer with room temperature conductivities greater than 10 -4 S/cm. In general, increased concentrations of BETI anions in these materials resulted in increased mechanical stability but decreased ionic mobility. The complexes and composite polymer electrolytes displayed excellent anodic stability up to +4.5 V (vs. Li + /Li) and exhibited breakdown voltages ≥+5.5 V (vs. Li + /Li) on stainless steel electrodes.

Enhanced Functionality for Donor–Acceptor Oligothiophenes by means of Inclusion of BODIPY: Synthesis, Electrochemistry, Photophysics, and Model Chemistry

We have synthesized several new push-pull oligothiophenes based on the boron dipyrromethene (BODIPY) moiety as the electron acceptor and the more well-known oligothiophenes substituted with N,N-dialkylamino functions to enhance their electron-donor ability. A complete characterization of the electronic properties has been carried out; it consists of their photophysical, electrochemical, and vibrational properties. The compounds have been studied after chemical treatment with acids and after oxidation. In this regard, they can be termed as NIR dyes and amphoteric redox electroactive molecules. We have described the presence of dual fluorescence in these molecules and fluorescence quenching either by energy transfer or, in the push-pull molecules, by electron exchange. The combination of electrochemical and proton reversibility along with the interesting optical properties of the new species offer an interesting platform for sensor and material applications.

Comparison of Thiophene–Pyrrole Oligomers with Oligothiophenes: A Joint Experimental and Theoretical Investigation of Their Structural and Spectroscopic Properties

We have prepared a new series of mixed thiophene-pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum-chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. The balance between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus aromatic competition.

Understanding optoelectronic properties of cyano-terminated oligothiophenes in the context of intramolecular charge transfer

In this paper we have prepared a new series of oligothiophenes capped with hexyl groups and a variety of strong acceptors, mainly cyanovinyl moieties. An exhaustive analysis of the absorption, photophysical, electrochemical, solid state, nonlinear optical and vibrational properties has been presented guided by theoretical calculations. The investigation is centered on the efficiency of the intramolecular charge transfer (i.e., chain length and acceptor dependence) and its impact on all the relevant electronic, structural, optical, and vibrational properties. The most significant features imparted by the acceptors through the π-conjugated oligothiophene path are (i) intense visible electronic absorptions, (ii) tuned fluorescence wavelength emissions, (iii) solid state π-stacking, (iv) ambipolar redox behavior, (v) S(1) ⇝ S(0) internal conversion as being the major route for the deactivation of the excited state, and (vi) large electronic and vibrational contributions to their nonlinear optical response (hyperpolarizability). The analysis establishes connections between the different properties of the materials and structure-function relationships useful in organic electronics.

Wind to Ammonia: Electrochemical Processes in Room Temperature Ionic Liquids

In this project, an alternative approach to synthesize ammonia electrochemically from wind energy, nitrogen gas, and ethanol is reported. Initial electrolyses have been attempted using room temperature ionic liquids (RTILs) as the electrolyte solvent in the presence of lithium ions. Bis(trifluoromethanesulfonyl)imide salts of 1-Ethyl-3-methylimidizolium (EMI-TFSI) and 1-Butyl-1methylpyrrolidinium (PYR14-TFSI) were tested in this investigation. These results are compared to the use of tetrahydrofuran as the solvent. The data suggests EMI-TFSI is not an appropriate ionic liquid for the lithium mediated reduction of N2, whereas the increased electrochemical stability of PYR14-TFSI offers greater promise. Current efficiencies (3.8%) for NH3 formation in THF are consistently higher than PYR14-TFSI at atmospheric temperatures and pressures. The amount of ammonia synthesized was quantified by performing the Berthelot reaction.

Ionic conductivity of a poly(vinylpyridinium)/silver iodide solid polymer electrolyte system

Abstract A series of quaternized poly(2-vinylpyridine) (PVP) polymers has been synthesized with the general formula [(PVP) R ]I, where R =H, Me, Bu. Addition of AgI to the polymers results in new silver ion conducting solid polymer materials. Conductivities as high as 6×10 −3 S/cm have been observed for the 3:1 AgI/[(PVP)Me]I composition. Analogous materials with a 3:1 composition for the protonated and butyl-substituted polymers display lower conductivities near 2×10 −4 S/cm. Conductivity studies, as a function of temperature, show these materials to be thermodynamically stable with a low activation energy for ion conduction. Differential scanning calorimetry experiments suggest that a new phase with the general formula (PVP) R Ag 3 I 4 forms with silver ions in a new amorphous state.

UV - Vis, IR, Raman and theoretical characterization of a novel quinoid oligothiophene molecular material

A quinoid-type oligothiophene, 3 0 ,4 0 -dibutyl-5,5 00 -bis(dicyanomethylene)-5,5 00 -dihidro-2,2 0 :5 0 ,2 00 -terthiophene, which can be viewed as an analog of TCNQ, has been investigated by spectroelectrochemistry and density functional theory calculations, in its neutral and dianionic states. Electrochemical data show that the molecule can be both reduced and oxidized at relatively low potentials. Upon reduction, both experiments and theory agree well with the generation of a dianionic charged species. The model shows that the electronic structure of the dianion is consistent with two anionic dicyanomethylene groups attached to a central terthienyl spine having an aromatic structure. The two negatively charged dicyanomethylene groups conjugate with the terthiophene allowing for the extension of the p-delocalized system over the whole molecule. The stability of the dianionic species, due to its aromatic character, gives support to the low value for the electrochemical two-electron reduction process. Infrared spectra of the neutral and of the dianion species have been assigned and correlated. q 2003 Elsevier Science B.V. All rights reserved.

Exploration of the electronic structure of dendrimerlike acetylene-bridged oligothiophenes by correlating Raman spectroscopy, electrochemistry, and theory

A series of radial thiophene-based structures consisting of a central benzene or thiophene ring surrounded by acetylene-bridged terthienyl arms has been investigated by physical and theoretical methods. Fourier transform Raman spectroscopy of the neutral solids shows that the terthiophene arms are weakly coupled across the core (benzene plus acetylene groups) likely due to cross-conjugation or meta-conjugation effects that may prevent full delocalization. By increasing the number of arms around the central ring, the electronic structure of the molecules seems to be affected only at the core, whereas the outer terthiophene arms remain almost unaltered. Raman spectroelectrochemistry and quantum chemical calculations provide further insight into the charge delocalization of the oxidized species. There is no evidence to suggest that these oxidized forms, obtained upon electrochemical doping of the molecules, show charge delocalization across the core.

Polyelectrolyte Composite Materials with LiPF6 and Tetraglyme

The synthesis and properties of a new type of polymer gel electrolyte are discussed. The composite electrolytes consist of equimolar amounts of LiPF 6 and tetraglyme (G4) to create [Li(G4)]PF 6 which is added to a polyelectrolyte matrix. These materials display room-temperature conductivities > 10 - 4 S/cm and posses an electrochemical stability of greater than 5.0 V vs. Li + /Li.

Benzodithiophene homopolymers via direct (hetero)arylation polymerization

Direct (hetero)arylation polymerization (DHAP) of a monobrominated benzo[1,2-b:4,5-b′]dithiophene monomer using the Herrmann–Beller catalyst with a tertiary phosphine provided benzodithiophene homopolymers in good yields. Employing both P(o-OMePh)3 and P(o-NMe2Ph)3 as the phosphine ligands gave well-defined polymers—with the later phosphine providing a higher molecular weight polymer. The preparation of a benzodithiophene (BDT) trimer was used to assist in the assignment of the 1H NMR spectra of the synthesized polymers which show largely defect-free couplings. The optical spectra of polymers formed via DHAP and those prepared using traditional Stille couplings are essentially identical, which further confirms the presence of well-defined BDT–BDT couplings along the conjugated polymer chain. These results confirm that carboxylic acid additives are not always necessary to suppress defects in DHAP polymerizations and that DHAP is a viable alternative to traditional Stille coupling for the preparation of benzodithiophene homopolymers.