Stefanie Maier

Evolution and evaluation of the polymer/nanotube composite

Abstract Composite structures, using MWNT and SWNT and the polymer (PmPV) exhibit properties which enhance those of the individual components. The polymer PmPV can act as an organic filter for the multiwalled system where the MWNT are indefinitely suspended in the polymer solution while the carbonaceous material falls out of solution. Raman measurements of this show a complete reduction of the amorphous line at 1350 cm-1. We see that we can alter the luminescence quantum yield of the composite, where the effects are different depending on which nanotubes are used. When we examine the SWNT/PmPV the quantum yield is increased. The MWNT composite also shows strong non-linear optical signal. The pristine polymer has an χ (3) of 10 −11 esu whereas the composite χ (3) is -10 −10 esu.

Investigation of different synthetic routes to and structure–property relationships of poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene)

The synthesis of poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) by Horner–Emmons and Wittig condensation polymerisation in three different solvents is described. The chemical and optical properties of the derivatives thus formed are analysed, especially in relation to the differences in the cis∶trans ratio of the vinylene bonds. Although they all have the same chemical composition, it is found that their chemical and optical properties vary. NMR studies show that the morphologies of the polymers are different, due to the differences in the cis∶trans ratio of the vinylene bonds. It is found that the derivatives produced by Horner condensation contain a majority of trans bonds, and these derivatives show different spectral characteristics to the Wittig derivatives. The ability of the polymers to disperse carbon nanotubes is also studied. Here, not only is the synthetic route important, but the solvent used also plays a role. The derivatives that are produced by the Horner condensation route in DMF or chlorobenzene are found to have the best binding capabilities with carbon nanotubes.

Synthesis and optical properties of phenylene-vinylene copolymers

Abstract A series of soluble phenylene-vinylene copolymers have been prepared by four different methods. Two of these methods use the Wittig reaction in two different solvents, whereas the other two were prepared by the Horner reaction using the same two solvents. The method of preparation was found to affect the cis/trans vinylene bond ratio and also the molecular weight characteristics of the polymer. Some of the polymers form high molecular weight cyclic oligomers. The optical properties of the polymers were investigated and compared. Concentration dependant fluorescence studies were done. In particular one polymer (Poly(m-phenylene-co-2,5-dioctoxy-p-phenylene-vinylene) or WToIPmPV prepared by the Wittig route in Toluene exhibited behaviour characteristic of an aggregate luminescence.

Systematic trends in the synthesis of (meta-phenylene vinylene) copolymers

A systematic investigation of the synthesis of poly(m-phenylene vinylene-co-2,5-dioctyloxy-p-phenylene vinylene) (DOP-PmPV) by Wittig-Horner condensation polymerisation reactions is presented. Large variations in yield, molecular weight distribution and optical properties in the reaction products are obtained and studies on varying reaction temperature suggest that there is an optimum temperature for this reaction. Substitution of one of the octyloxy side chains by a methoxy group yields polymer of the type MOP-PmPV. They show similar optical properties to the DOP-PmPV polymers but are found to be of lower molecular weight.

Preparation and nonlinear optical properties of phthalocyanine nanocrystals

Zinc-2, 9,16,23 -tetra- tert-butyl-29H, 31H -phthalocyanines and Zinc-2, 9,16,23-tetrakis-(phenylthio)-29H, 31H-phthalocyanines were recrystallized from an acetone solution to give regular shaped spherical particles of 50nm diameter, confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). A peak broadening of the Q-Band and a shift of the B-Band in the UV-Visible absorption spectrum combined with a significant fluorescence quenching was observed. The z-scan technique was used to investigate the non-linear optical properties and an increase of approximately 200% in the ratio of excited to ground state absorption cross sections in the crystal state was observed indicative of a significant increase in the optical limiting response of the crystals compared to the monomers.

Non-linear absorption of alkylsulfonyl metallophthalocyanines

Z-scan experiments have been carried out over two series of novel symmetrically and unsymmetrically substituted alkylsulfonyl metallophthalocyanines. Non-linear absorption coefficients and excited state to ground state absorption cross section ratios (σ ex /σ 0 ) have been assessed for these materials. The results point out that electron-withdrawing substituents have a negative effect on the non-linear absorption behaviour of phthalocyanines.

The optical gain and effective stimulated emission cross-section for dimethoxy-PmPV and dimethyl-PmPV-ONV copolymers in toluene solution

We report amplified spontaneous emission from the copolymers poly{m-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(3,4-dimethyloxy phenyl) vinylene]} (dimethoxy-PmPV) and poly{m- phenylene-co-[1,5-dioctyloxy-2,6-naphthylene-bis-2(3,4-dimethyl phenyl) vinylene]} (dimethyl-PmPV-ONV) in toluene. The copolymers are related to poly(phenylene vinylene) and have been synthesized via the Horner?Emmons polycondensation reaction. The optical gain determined from the amplified spontaneous emission intensity is dependent on the excited stripe length. Net gains of 3.4 ? 0.2 and 0.3 ? 0.3 cm?1 were measured for dimethoxy-PmPV and dimethyl-PmPV-ONV respectively under nanosecond pulse excitation. The gain for rhodamine 6G was also measured under the same experimental conditions and was used to determine the stimulated emission cross-sections for both polymers; these were found to be ?se (peak) = 2.3 ? 10?18 cm2 for dimethoxy-PmPV and ?se (peak) = 2 ? 10?20 cm2 for dimethyl-PmPV-ONV.

Bulky sidegroup polymers – synthesis and characterisation

A series of conjugated polymers related to poly(phenylenevinylene) PPV was synthesised and characterised. These polymers contain phenylene moieties attached to the vinylene unit with various substitution patterns to obtain very complex systems. Some polymers only contain phenylene units along the polymer chain whereas for some of the derivatives naphthalene units were introduced into the backbone. Additionally, some derivatives were prepared by varying para and meta substitution patterns. The influences of different structural alterations on the thermal behaviour, the optical properties and electrochemical behaviour are investigated. In general, the polymers are temperature-stable up to 350°C, emit in the blue to green region of the visible spectrum and contain varying oxidation and reduction potentials depending on the substitution pattern.

Property-Structure Relationships of Some Derivatives of Poly (m- phenylene vinylene)

A derivative of poly (m-phenylene vinylene-co-2, 5-dioctyloxy-p-phenylene vinylene) is synthesized using two types of condensation polymerisation reactions, namely Horner-Eammons and Wittig, in three different solvents, toluene, dimethhylformamide (DMF) and chlorobenzene. Although the derivatives formed by each reaction have the same chemical composition it is found that their chemical and optical properties vary. NMR studies show that the morphologies of the polymers are different, due to the differences in cis-trans bond ratio of the vinylene bonds. It is found that the derivatives produced by Horner condensation contain a majority of trans bonds and these derivatives show different spectral characteristics to the Wittig derivatives. The ability of the polymers to disperse carbon nanotubes is also studied. Here, not only is the synthetic route important, but the solvent used also plays a role. The derivatives that are produced by the Horner condensation route in DMF or chlorobenzene are found to have the best binding capabilities with carbon nanotubes.

Solvent effects on the luminescent properties of conjugated molecules

The photoluminescent yield and lifetime of 2,5-dioctyl-p-distyrylbenzene is shown to vary significantly in a range of organic solvents. This variation is seen to correlate well with the overlap of the vibrational spectrum of the molecule with that of the solvent. This overlap is proposed as a gauge of the nonradiative decay processes in dilute solution. In solutions of higher concentration and of the polymer PmPV, this correlation is lost, however. The loss of correlation is attributed to a departure from single molecular photophysics as a result of aggregation.