William A. Feld

Hydrogen Storage Based on Physisorption

Physisorption of molecular hydrogen based on neutral and negatively charged aromatic molecular systems has been evaluated using ab initio calculations to estimate the binding energy, DeltaH, and DeltaG at 298 ( approximately 77 bar) and 77 K (45 bar) in order to compare calculated results with experimental measurements of hydrogen adsorption. The molecular systems used in this study were corannulene (C(20)H(10)), dicyclopenta[def,jkl]triphenylene (C(20)H(10)), 5,8-dioxo-5,8-dihydroindeno[2,1-c]fluorene (C(20)H(10)O(2)), 6-hexyl-5,8-dioxo-5,8-dihydroindeno[2,1-c]fluorene (C(26)H(22)O(2)), coronene (C(24)H(12)), dilithium phthalocyanine (Li(2)Pc, C(32)H(16)Li(2)N(8)), tetrabutylammonium lithium phthalocyanine (TBA-LiPc, C(48)H(52)LiN(9)), and tetramethylammonium lithium phthalocyanine (TMA-LiPc, C(36)H(28)LiN(9)). It was found (a) that the calculated term that corrects 0 K electronic energies to give Gibbs energies (thermal correction to Gibbs energy, TCGE) serves as a good approximation of the adsorbent binding energy required in order for a physisorption process to be thermodynamically allowed and (b) that the binding energy for neutral aromatic molecules varies as a function of curvature (e.g., corannulene versus coronene) or if electron-withdrawing or -donating groups are part of the adsorbent. A negatively charged aromatic ring, the lithium phthalocyanine complex anion, [LiPc](-), introduces charge-induced dipole interactions into the adsorption process, resulting in a doubling of the binding energy of Li(2)Pc relative to corannulene. Experimental hydrogen adsorption results for Li(2)Pc, which are consistent with MD simulation results using chi-Li(2)Pc to simulate the adsorbent, suggest that only one side of the phthalocyanine ring is used in the adsorption process. The introduction of a tetrabutylammonium cation as a replacement for one lithium ion in Li(2)Pc has the effect of increasing the number of hydrogen molecules adsorbed from 10 (3.80 wt %) for Li(2)Pc to 24 (5.93 wt %) at 77 K and 45 bar, suggesting that both sides of the phthalocyanine ring are available for hydrogen adsorption. MD simulations of layered tetramethylammonium lithium phthalocyanine molecular systems illustrate that doubling the wt % H(2) adsorbed is possible via such a system. Ab initio calculations also suggest that layered or sandwich structures can result in significant reductions in the pressure required for hydrogen adsorption.

A Facile Synthesis of 3,4-Dialkoxythiophenes

Abstract Dialkylation of diethyl 3,4-dihydroxythiophenedicarboxylate followed by ester hydrolysis and acid decarboxylation provides a general route to 3,4-dialkoxythiophenes.

Synthesis and structure-property relationships of bismaleimides containing oxyalkylene linkages

Abstract The synthesis and the effects of variation in structure on the resulting processing and final properties of a series of bismaleimides based on diamines containing flexible units of variable length or flexible units of fixed length with varying-length pendent groups is presented. Thermal analysis, parallel-plate rheometry and torsion impregnated-cloth analysis were utilized to characterize the processing, cure and final properties. It was found that, by appropriately choosing the size of main-chain and pendent aliphatic groups in bismaleimides containing oxyalkylene linkages, one can control the breadth of the cure window without adversely affecting either thermal stability or final glass transition temperatures.

A General and Efficient Synthesis of 2-Phenylbenzothiazoles From Diphenyl Disulfides

Abstract Benzothiazoles containing a substituted-phenyl at the 2 position can be synthesized cleanly and efficiently from the corresponding bis(2-aminophenyl) disulfide. Bis(2-aminophenyl) disulfides represent a stable source of 2-aminobenzenethiols.

Light-emitting diodes based on poly(2,3-diphenyl-1,4-phenylene vinylene)

In this paper we report polymer light-emitting diodes based on (2,3-diphenyl-1,4-phenylene vinylene) (DP-PPV), a novel π-conjugated polymer made by using the chlorine precursor route (CPR). Thin films of the precursor polymer were formed by spin-casting on indium-tin oxide (ITO) coated glass substrates, followed by thermal conversion to give DP-PPV thin films. Single layer DP-PPV LEDs were completed by thermally evaporating magnesium (Mg) electrodes. The electroluminescent characteristics of ITO/DP-PPV/Mg devices as well as variations between precursor polymer batches are presented. Bilayer LEDs were also made, for which tris(8-hydroxyquinoline)aluminum (Alq3) was thermally sublimed on the fully converted DP-PPV films in vacuum, followed by Mg deposition. Both significant improvement in the quantum efficiency (up to 0.7% ph/el) and a reduction in the turn-on voltage of the device were found upon incorporation of the Alq3 layer. These observations suggest that Alq3 enhances the injection of electrons and also participates in the recombination process.

A layer-wise topographic study of a polymeric light-emitting diode: indium-tin oxide/poly (2,3-diphenyl-p-phenylene vinylene) / Ag

Abstract Scanning tunneling microscopy was used to characterize surface topographies relevant to polymeric light-emitting diodes (LEDs) whose active medium is a thin film of poly(2,3-diphenyl- p -phenylene vinylene) (DP-PPV). We performed a sequence of topographic studies on an indium-tin oxide (ITO) substrate, a DP-PPV film deposited on the ITO substrate, and a Ag layer of thickness of about 100 A as evaporated on the DP-PPV film. ITO showed a granular structure, DP-PPV exhibited a fibrous-like bundled structure, and the Ag layer formed clusters whose surface roughness was comparable to the layer thickness. The different surface topographies were quantified by using the scaling of the height-height correlation functions.

Composite Cathode with Li2Pc

Computational chemistry calculations performed with Gaussian 98 were used to develop an experimental method that facilitates ionic connection between the solid-state electrolyte dilithium phthalocyanine (Li 2 Pc) and manganese dioxide (MnO 2 ). The planar configuration of the phthalocyanine ring and the fact that the lithium ions are very close to the ring may sterically hinder effective ionic coupling between Li 2 Pc and any potential cathode. This same argument has been used for understanding the insertion and removal of magnesium from water solutions of deuteroporphyrins. Calculated results show that lithium ions are drawn closer to the phthalocyanine ring upon formation of (Li 2 Pc) 2 via molecular self-assembly when compared to the single-molecule Li 2 Pc. However, extension of lithium ions above the planar phthalocyanine ring in (Li 2 Pc) 2 can be enhanced through formation of a complex at the axial position above lithium. Calculations show that corannulene at the axial position above lithium forms an asymmetric structure with (Li 2 Pc) 2 and extends lithium further above the ring. To test the theoretical results, an electrically conducting carbon with a curved lattice was used in the fabrication of an all solid-state electrochemical cell with a lithium metal foil anode, Li 2 Pc electrolyte, and a MnO 2 cathode. Slow-scan-rate cyclic voltammograms of a Li x MnO 2 cathode demonstrate the charging and discharging of cells.

Synthesis and Characterization of Organo-Soluble, Thermally-Curable, Phenylated Aromatic Polyimides

Phenylated aromatic polyimides have been prepared in two steps by the Diels-Alder polymerization of biscyclopentadienones with dimaleimides followed by dehydrogenation and in one step by the polymerization of phenylated bis(phthalic anhydrides) with diamines. Although the polymers prepared by both routes were soluble in chlorinated-hydrocarbon solvents, the latter afforded considerably higher molecular weight materials. Polyimides obtained in this manner had intrinsic viscosities as high as 4.0 dl/g and glass transition temperatures that ranged from 238 to 466°C. Thermogravimetric analysis thermograms of the polymers in air and nitrogen atmospheres showed no weight loss until near 530°C. Two new ethynyl-substituted diamines, 4(2,4-diaminophenoxy)phenylacetylene (1) and 3,5-diaminodiphenylacetylene (2), have been synthesized and polymerized with a phenylated bis(phthalic anhydride). The polymer prepared with diamine 1 underwent cross-linking at 250°C without the evolution of volatile byproducts, while the polymer prepared with diamine 2 underwent an analogous cure at 350°C. A phenylated bis(phthalic anhydride) has also been copolymerized with pyromellitic dianhydride (PMDA) and 4,4’-diaminodiphenyl ether to afford soluble copolymers that contain as high as 50 mole % PMDA.

Molecular Dynamics Simulations of H2 Adsorption in Tetramethyl Ammonium Lithium Phthalocyanine Crystalline Structures

Tetramethyl ammonium lithium phthalocyanine is explored as a potential material for storage of molecular hydrogen. Density functional theory calculations are used to investigate the molecular structure and the dimer conformation. Additional scans performed to determine the interactions of a H2 molecule located at various distances from the molecular sites are used to generate a simple force field including dipole-induced-dipole interactions. This force field is employed in molecular dynamics simulations to calculate adsorption isotherms at various pressures. The regions of strongest adsorption are quantified as functions of temperature, pressure, and separation between molecules in the adsorbent phase, and compared to the regions of strongest binding energy as given by the proposed force field. It is found that the total adsorption could not be predicted only from the spatial distribution of the strongest binding energies; the available volume is the other contributing factor even if the volume includes regions of much lower binding energy. The results suggest that the complex anion is primarily involved in the adsorption process with molecular hydrogen, whereas the cation serves to provide access for hydrogen adsorption in both sides of the anion molecular plane, and spacing between the planes.

The Phase-Transfer Catalyzed Synthesis of Bis(4-Aryloxy-3-Nitrophenyl) Sulfones

Abstract Ten bis(4-aryloxy-3-nitrophenyl) sulfones were synthesized via a phase-transfer catalyzed, nucleophilic displacement reaction involving phenoxides and bis(4-chloro-3-nitrophenyl) sulfone.