Martin Pomerantz

Self-doped conducting copolymers: a charge and mass transport study of poly{pyrrole-CO[3-(pyrrol-1-YL)propanesulfonate]}

Abstract A self-doped copolymer of pyrrole, poly{pyrrole-co-[3-(pyrrol-1-yl)propanesulfonate]}, in which the charge compensating counterion is bound covalently to the polymer main chain, has been prepared and the charge and mass transport in the polymer during redox switching has been investigated using chronocoulometry and microgravimetry as a function of the supporting electrolyte The results are compared with the behavior of polypyrrole under similar conditions It is shown that within this new family of materials, called “self-doped conductive polymers”, ion mobility is restricted to cationic species and thus the polymer can be viewed as an ion-specific membrane This is in contrast to the case of polypyrrole, where a more complex behavior prevails The charge passed during the chronocoulometric experiment varies as tα where 0.2

Poly(2-decylthieno[3,4-b]thiophene). A new soluble low-bandgap conducting polymer

Abstract A new soluble low-bandgap conducting polymer, poly(2-decylthieno[3,4- b ]thiophene) ( 5 ), has been prepared by a multistep synthetic sequence. The vis-NIR spectra of a film of 5 showed λ max = 738 nm with a band-edge bandgap of 1.2 eV. FeCl 3 doping of the film gave a conductivity of 7.2 × 10 −2 S cm − . The GPC molecular weight was n = 30,000.

Processable polymers and copolymers of 3-alkylthiophenes and their blends

Abstract Poly(3-alkylthiophenes) have been prepared using anhydrous FeCl 3 in CHCl 3 while dry air was bubbled through the reaction mixture. Molecular weight studies via GPC, using polystyrene standards in conjunction with RI and UV detection along with absolute determinations using a multiangle laser light scattering (MALLS) detector, have shown these materials are of high molecular weight (M w of up to 400,000) and relatively low polydispersity ( M w M n ). Further, the MALLS detector (absolute molecular weights) provides weight average molecular weights 2–5 times larger than those obtained using polystyrene standards showing that polystyrene is a rather poor standard for these materials. A series of copolymers of the 3-alkylthiophenes was prepared using a 1:1 molar feed ratio of the two monomers and the molecular weights of the materials decreased with decreasing side chain length. Poly(3-alkylthiophenes) were processable via a variety of methods, including melt spinning to form soft fibers. The films and fibers were dopable with typical oxidants to conductivities of up to 5 Ω −1 cm −1 . The solution pulled fibers were observed to be birefringent with considerable orientation along the fiber axis. EDAX studies have shown that the doping of melt-spun Fibers was quite uniform. Blends of poly(3-decylthiophene) with low density polyethylene have been prepared and melt-spun into fibers. Blends prepared by melt-blending the components were seen by electron microscopy to be phase separated into large domains while those prepared from xylene solution were much more uniform. Spinning was easier with the blends and the fibers spun from the blend prepared from xylene solution was seen to be birefringent with considerable orientation along the fiber axis. Doping of the melt spun fibers obtained from xylene solution formed blends gave conductivities of ca. 10 −1 − 1 Ω −1 cm −1 while those produced from the melt formed blends were non-conducting.

Planar 2,2′-bithiophenes with 3,3′- and 3,3′,4,4′-substituents. A computational study

Abstract Ab initio calculations have shown that when carbonyl groups are incorporated into the 3- and 3′-positions of bithiophenes, as part of five-membered rings, the bithiophene system is planar. This is due to electrostatic attraction between the carbonyl oxygen and the sulfur atom in the adjacent ring. In the analogous systems containing a CH 2 group in place of the carbonyl, or containing six-membered rather than five-membered rings, the bithiophenes are twisted. This has implications for preparing planar polythiophenes.

Structure and significance of some twenty-one and twenty-two carbon petroleum steranes

Abstract Two steranes, commonly found in petroleum and petroleum source rocks, have been identified. One is the 5α, 14β, 17βH stereoisomer of pregnane called diginane and the other is 20-methyldiginane. These compounds are detected in the saturated hydrocarbon fraction of many crude oils by capillary gas chromatography-mass spectrometry. Both virtually coelute from a capillary gas chromatography column with a 5α, 14α, 17αH stereoisomer. The amount of the two diginanes in a petroleum sample, relative to the abundance of steranes having from twenty-seven to twenty-nine carbon atoms, seems to be an apparent indicator of thermal maturity.

New processable low band-gap, conjugated polyheterocycles

Abstract Poly(2,3-dihexylthieno[3,4-b]pyrazine) (2b) has been prepared by ferric chloride polymerization of 2,3-dihexylthieno[3,4-b]pyrazine(4) and studied. It is a dark blue-black soluble material which becomes light yellow in the doped state as either a solution or film. Doped films can be cast directly from solution. The band-gap, obtained from the absorption edge, is ca. 0.86–1.02 eV as the film and 1.14 eV as a CHCl3 solution. This value of about 0.95±0.1 eV is lower than that of poly(isothianaphthene) and poly(5-decylisothianaphthene), which we report here. It is consistent with theoretical predictions and is one of the lowest band-gaps reported to date. When doped with nitrosonium tetrafluoroborate the films show conductivities of up to 3.6 × 10−2 S cm−1. Poly(50decylisothianaphthene) {(1b; poly(5-decylbenzo[c]thiophene)} has been prepared by FeCl3 oxidation of 5-decyl-1,3-dihyhrobenzo[c]thiophene (6). It is a soluble dark blue-black material which forms a light yellow transparent solution when doped.

Poly(alkyl thiophene-3-carboxylates). Synthesis, properties and electroluminescence studies of polythiophenes containing a carbonyl group directly attached to the ring

Improved synthetic methodology for poly(3-hexyl- and 3-octyloxycarbonylthiophene-2,5-diyl) (1a and 1b) is reported. n =6700 and 9400 ( w / n =2.5 and 3.2), λ max for fluorescence emission=600 and 610 nm and λ max for electroluminescence=600 and 615 nm, for 1a and 1b respectively. The 1 H NMR spectra required that pentads be considered to explain the spectra. That is the four nearest neighbours to a given ring influence the 1 H NMR spectrum. Electroluminescence efficiencies of 0.016% and 0.018% were observed for devices made from 1a and 1b, respectively. A bilayer device of ITO/poly(3-octylthiophene)/1b/Al emitted at 646 nm, the same wavelength where poly(3-octylthiophene) itself emits. The efficiency was low but was an order of magnitude greater than for poly(3-octylthiophene) itself. Regioregular (HH-TT) poly(4,4′-bis(hexyl- and octyloxycarbonyl)[2,2′-bithiophene]-5,5′-diyl) (3a and 3b) were also prepared via the Ullmann reaction and n =7900 and 11000 respectively. Films of 3a and 3b were yellow in color and showed λ max =377 and 381 nm respectively, about 55-80 nm blue shifted compared with 1a and 1b. This is due to the large rotational barrier in the HH dyads which reduces the effective conjugation length in 3a and 3b. 3a and 3b showed bright fluorescence and electroluminescence with emission of yellow light. Electroluminescence efficiencies were 8.5×10 –3 % and 4.7×10 –3 %, respectively.

Studies of planar poly(3,4-disubstituted-thiophenes)

Ab initio calculations on bithiophenes, confirmed by X-ray analysis, show how to design polythiophenes with C=O groups in both the 3- and 4-positions which are completely planar. Planarity results from coulombic attraction between a carbonyl O and a nearby S. A model bithiophene and two polythiophene imides which are potentially completely planar have been prepared and studied.

Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films

Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency.

Ester substituted bithiophenes. Abnormally low dihedral angle and rotation barrier due to dipolar stabilization

Abstract Ab initio calculations [3−21G (*) ] on dimethyl 2, 2′-bithiophene-4, 4′-dicar☐ylate ( 3 ), dimethyl 2, 2′-bithiophene-3, 4′-dicar☐ylate ( 4 ) and dimethyl 2, 2′-bithiophene-3, 3′-dicar☐ylate ( 5 ) have revealed that in 4 there is an abnormally small dihedral angle between the thiophene rings and an abnormally low barrier to rotation around the thiophene-thiophene single bond. This is due to a favorable coulombic interaction of the negative carbonyl oxygen and the positive sulfur of the adjacent ring which helps to flatten and bend the ground state and lower the rotation barrier. Ab inito calculations [3–21G (*) ] show a favorable coulombic interaction between the negative carbonyl oxygen and the positive sulfur of the adjacent ring in dimethyl 2, 2′-bithiophene-3, 4′-dicar☐ylate ( 4 ), which helps to flatten the ground state considerably and substantially lower the thiophene-thiophene rotation barrier. Download full-size image