D. Bloor

Characterization of polypyrrole electropolymerized on different electrodes

Abstract Polypyrrole containing the toluenesulphonate counter-ion has been electrochemically polymerized on a wide range of metallic electrodes, including platinum, titanium, aluminium, mild steel and brass. The oxidation behaviour of pyrrrole monomer in the presence of these electrodes has been investigated and the influence of metal oxide layers is discussed. The redox behaviour of the polymers prepared on different electrodes suggests that the reaction appears quasi-reversible for all the oxidizable metal electrodes and only in the case of platinum is the reaction simply diffusion-controlled. Chemical and physical characterization of the materials is also presented and the presence of a distinct fibrillar second phase is reported for the first time.

Fundamental and defect properties of a crystalline conjugated polymer

Abstract The fundamental and defect properties of a diacetylene polymer have been established by spectroscopic observations of samples ranging from large single crystals to amorphous powders. These results agree well with previous models of defect states of conjugated chains by the nature of the fundamental excited electronic state has not yet been clearly established.

The influence of unusual counterions on the electrochemistry and physical properties of polypyrrole

A series of different counterions have been incorporated into polypyrrole electrochemically. These include toluenesulphonate (TS), pyrenesulphonate (PSA), Pyrene-1,3,6,8-tetrasulphonate (PTSA), dodecylbenzenesulphonate (DBS), 1,2-bis (decyloxycarbonyl)ethane-1-sulphonate (DOCES), octachloro-dirhenate (Re2Cl8) and tetraphenylborate (TPB). Electrochemical redox behaviour of the pyrrole monomer and the polypyrrole incorporating these different anions was investigated and is discussed. From scanning electron microscopy (SEM), it is shown that the different counterions incorporated strongly affect the morphology of the polymer films, they vary from fully dense to open structures. Chemical and physical characterization of the materials is presented and suggests that the sizes of the different counterions incorporated also influence the polymer chain structures, packings and their thermal stabilities. The pyrrole to counterion stoichiometries are very different, ranging from 1 to 13. In most cases, the redox potential of the polymer can be related to the size of the counterion but the electrical conductivity, which ranges from 2×10−3 to 50 Scm−1, is not simply related to the counterion but is dependent on both chain structure and bulk morphology.

Optical properties of fully and partially polymerized bis (p-toluene sulphonate) diacetylene crystals

Abstract The optical spectra of fully and partially polymerized crystals of bis ( p -toluene sulphonate) diacetylene have been measured between 4.2 and 330 K. The electronic absorption of the conjugated polymer backbone occurs at about 2 eV and is split into two components below 160 K in both fully and partially polymerized samples. The origin of this splitting is discussed.

The synthesis of ferrocenyl compounds with second-order optical non-linearities

Abstract A series of new donor-acceptor compounds of the form (η-C 5 H 5 )Fe(η-C 5 H 4 ) CHCHR, where R is a π-acceptor group and the ferrocenyl moiety is a donor has been synthesized. Reaction of the ylide (η-C 5 H 5 )Fe(η-C 5 H 4 )CHP(C 6 H 5 ) 3 ( 3 ), generated in situ with various aldehydes, proceeds smoothly. The ferrocenyl compounds were screened for second harmonic generation efficiencies using 1.907μm light generated by Raman shifting the 1.064μm light from an Nd-YAG laser, using a high pressure hydrogen cell. Several of the compounds had efficiencies greater than the urea reference standard.

Electronic energy levels of polyaniline

The electronic energy levels of polyaniline (PANi) thin films have been investigated using UV/VIS/NIR spectroscopy and X-ray photo-electron spectroscopy. The experimental results have been compared with the latest theoretical band structure calculations for the polyemeraldine salt form of PANi, and also the various structural and electronic changes thought to occur during electrochemical oxidation of the polymer.

A study of the electronic excited states of fully and partially polymerized bis(p-toluene sulphonate) diacetylene crystals by resonant raman scattering

Abstract Certain lines in the resonant Raman spectra of fully and partially polymerized bis ( p -toluene sulphonate) single crystals are observed to split into two components below 160 K. The two components experience maximum intensity enhancement at different frequencies of the incident dye laser beam. The possible origins of the splitting are discussed.

Observation of paramagnetic triplet species during the thermal polymerization of bis(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol

Abstract ESR observations of single crystals of bis( p -toluene sulphonate) of 2,4-hexadiyne-1,6-diol during solid state thermal polymerization at 60°C reveal spectra characteristic of paramagnetic triplet species. One centre has large values of the fine structure tensor and maximum intensity at maximum polymerization rate. The other has small fine structure values and anneals out slowly after the period of rapid polymerization. The nature of these centres is discussed.

Efficient second-harmonic generation in single crystals of 2-(N,N-dimethylamino)-5-nitroacetanilide

Measurements of second-harmonic generation (SHG) from powders have indicated that 2-(N, N-dimethylamino)-5-nitroacetanilide (DAN) has a high second-order optical nonlinearity. This has been confirmed by the observation of efficient phase-matched SHG from a DAN single crystal. For 1-mJ pulses at 1.064 μm, a conversion efficiency of 20% has been measured for a crystal 2 mm thick. X-ray crystallographic analysis suggests that this high efficiency derives from a favorable molecular packing.

Second-order non-linear optical properties of diironalkenylidyne complexes; crystal structure of {(η-C5H5)2Fe2(CO)2(μ-CO)(μ-(E)CCHCHC6H4(p)-NMe2)}+BF4−

Abstract The second-order non-linear optical properties of a series of diironalkenylidyne complexes have been examined by the Kurtz powder technique. One compound, {(η-C5H5)2Fe2(CO)2(μ-CO)(μ-(E)CCHCHC6H4(p)-N(CH3)2)}+CF3SO3−, exhibited a powder efficiency for second harmonic generation 3.6 times that of a urea reference standard (ω = 1907 nm, 2ω = 953.5 nm). The crystal structure of {(η-C5H5)2Fe2(CO)2(μ-CO)(μ-(E)CCHCHC6H4(p)-N(CH3)2)}+BF4− has been determined.