Stephen Moratti | University of Otago (original) (raw)

Papers by Stephen Moratti

Journal of Biomedical Materials Research Part A, 2014

In developing a chitosan/dextran-based (CD) hydrogel as an adhesion prevention postsurgical aid, ... more In developing a chitosan/dextran-based (CD) hydrogel as an adhesion prevention postsurgical aid, the in vivo biodegradation rate, biodistribution, and inflammatory response are important parameters to the biomedical device design. Herein, for the first time, a CD hydrogel was prepared by mixing aqueous solutions of a near infrared (NIR) labeled succinylated chitosan (SC) and tritiated [(3) H] oxidized dextran (DA). The biodegradation and biodistribution of the NIR/[(3) H]-CD hydrogel was tracked noninvasively using NIR fluorescence imaging, and by liquid scintillation counting (LSC) of organs/tissues after subcutaneous injection in BALB/c mice. The inflammatory response was assessed by measuring serum cytokine levels using a Bio-plex assay and by histological examination of injection site tissue. Fluorescence imaging showed the hydrogel to degrade in under a week. LSC revealed the hydrogel to reside mainly at the injection site, and excreted primarily via the urine within the first 48 h. The CD hydrogel showed a mild inflammatory response as cytokine levels were comparable to saline injected controls. Histological examination of injection site tissue confirmed the cytokine results. In summary, the CD hydrogel's in vivo biodegradation rate, biodistribution, and inflammatory response was determined. Our results indicate that the CD hydrogel has an appropriate biocompatibility after s.c. administration. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2014.

Synthetic Metals, 1999

A new 2,3-dibutoxy-l,4-phenylene vinylene is reported with high photoluminescence (40%) and elect... more A new 2,3-dibutoxy-l,4-phenylene vinylene is reported with high photoluminescence (40%) and electroluminescence efficiencies. The unusual substitution pattern is effective in tuning the emission colour as the polymer exhibits unexpected blueshifted emission to the green region. Crystal structures of model oligomers (PL efficiencies 80%) and theoretical calculations on optimised geometry offer insight into these interesting properties.

Synthetic Metals, 2000

We report on the characterisation of the second order nonlinear optical properties of a semiflexi... more We report on the characterisation of the second order nonlinear optical properties of a semiflexible main chain random copolymer with a head to tail structure synthesised from 4-carboxy-4′-[N-(11-hydroxyundecyl)-N-methylamino]-azobenzene and hydroxybenzoic acid. This polymer exhibits a nematic liquid crystal mesophase with a nematic-isotropic transition temperature of 200°C. We find a complicated phase behaviour for the polymer and show that the polymer films be readily annealed into large homogeneously aligned monodomains in device configurations. We have carried out measurements of the field dependent poling behaviour by means of an ellipsometric set-up after Teng and Man. We find three distinctive field regions corresponding to different mechanisms in the response of the polymer chains. No saturation in the poling response can be detected for fields up to 108 V/m. Absolute values for χ(2) reach 80 pm/V. We analysed any potential χ(3) contribution to the total NLO signal and showed that this contribution can be neglected for our measurements.

Solid-state Electronics, 1996

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be... more Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics, both as electroluminescent diodes and also as photoconductive diodes. We discuss the present understanding of the operation of light-emitting diodes which use conjugated polymers for both charge transport and emission. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and thus, bring about electron-hole capture to generate excitons at this interface. The nature of these diodes allows fabrication of microcavity structures in which the emission characteristics of the polymer are strongly modified by the allowed cavity modes. This can be used to control the colour of emission and sharpness of the emission bands.

Synthetic Metals, 1999

A new series of porphyrin-containing PPV-copolymers have been synthesised. The porphyrin units ar... more A new series of porphyrin-containing PPV-copolymers have been synthesised. The porphyrin units are attached as a side group on the main chain, in an effort to attempt to control aggregation and consequent fluorescence quenching. Emission is red-shifted from that expected in dialkoxy-PPVs owing to an efficient exciton transfer to the fluorescent porphyrin unit, leading to a more useful red colour for RGB displays. The effects of the porphyrin concentration on the PL efficiencies will be reported.

Australian Journal of Chemistry, 1990

Synthetic Metals, 1999

Liquid crystalline phthalocyanines (Pc's) are promising materials for opto-electronic application... more Liquid crystalline phthalocyanines (Pc's) are promising materials for opto-electronic applications (e.g. solar cells, electrophotography) due to their high absorption coefficients in the long wavelength region of the optical spectrum and high charge carrier mobilities in the columnar mesophase. We report here the synthesis and properties, in particular the thermotropic phase behaviour, of a series of new octakis(alkylthio)-substituted pc's.

Synthetic Communications, 1990

Feist-Benary condensations to form furans are usually carried out by reacting an á-halo aldehyde ... more Feist-Benary condensations to form furans are usually carried out by reacting an á-halo aldehyde and a β-keto ester under basic conditions. However, yields are often poor, and the main product is often a dihydrofuranol requiring subsequent acid-catalysed dehydration to form the furan. The α-halo acetaldehyde is also difficult to prepare free of water when anhydrous reaction conditions are desired.

Molecular Simulation, 2005

Synthetic Metals, 1996

Results are presented which explore the synthesis, characterization and photoluminescence of new ... more Results are presented which explore the synthesis, characterization and photoluminescence of new types of conjugated copolymers which incorporate fused thiophene units. Such materials possess intense purple-red colours and some absorb in the near-infrared. The redox processes showed that the polymers were both p- and n-dopable.

Synthetic Metals, 1999

A range of onium salts were blended with conjugated polymers and exposed to visible light. Photoi... more A range of onium salts were blended with conjugated polymers and exposed to visible light. Photoinduced doping occurred with iodonium salts, but not with sulfonium salts. Cyclic voltammetry was used to study the reaction process. This loss of photoreaction holds promise for use in sensors and radiation detectors.

Synthetic Metals, 1996

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be... more Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics both as electroluminescent diodes and as photoconductive diodes. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and, thus, bring about electron-hole capture to generate excitons at this interface. We present results on the photophysical properties of the cyanosubstituted poly(phenylenevinylene)s which provide electron transport layers if these heterostructure devices; we find evidence for strong interchain interactions (excimer formation) for the neutral excited states in these polymers, with strong red shifts of the luminescence, though preserving high photoluminescence efficiencies.

Synthetic Metals, 1994

A new poly(phenylene-co-dialkoxyphenylene) derivative was synthesized by the Suzuki coupling of a... more A new poly(phenylene-co-dialkoxyphenylene) derivative was synthesized by the Suzuki coupling of aromatic bromoboronic acids. This showed strong violet photoluminescence (peak 415 nm) in the solid state and good solubility in organic solvents. A multilayer light-emitting diode was constructed with the structure indium-tin oxide/poly(p-phenylenevinylene)/polyphenylene/calcium. Efficient light emission was observed with a peak maximum in the blue region of the visible spectrum.

Chemistry-a European Journal, 1997

The early stages of rnetal/polymer interface formation between aluminum and poly (2,5,2',5'-tetra... more The early stages of rnetal/polymer interface formation between aluminum and poly (2,5,2',5'-tetrahexyloxy-8,7'-dicyanodi-~-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction. Fax: Int. code +(65)37-3366 (0 VCH Vrrlag~gerellschaff mhH 0-69451 Wernhrrm, l Y Y 7 OY47-653U/Y7/0302-0286.R I5 00+ 25/0 Chrm Eur J 1997, 3, No 2

Macromolecules, 2000

ABSTRACT We report the synthesis and electroluminescent properties of random poly(phenylenevinyle... more ABSTRACT We report the synthesis and electroluminescent properties of random poly(phenylenevinylene) copolymers, carrying fluorine substitutions. In particular, we used 2,3,5,6-tetrafluoro-1,4-phenylenevinylene and 2-methoxy-5-(2‘-ethylhexyloxy)-1,4-phenylenevinylene moieties. The ratios of the two copolymer units were varied between 5:95 and 27:75. Electrochemical measurements showed an increase of the oxidation and a decrease of the reduction potentials of the copolymers upon increase of the fluorine content, as expected for the electron withdrawing effect of fluorine on the conjugated π-electron system. The copolymers showed emission in the red-orange region, with maximum photoluminescence efficiencies of 6.7%. We also observed lower turn-on voltages and higher electroluminescence efficiencies for lower fluorine contents.

Macromolecular Symposia, 2009

A series of hydrogels were formed from the reaction between an amine functionalized succinyl chit... more A series of hydrogels were formed from the reaction between an amine functionalized succinyl chitosan and an oxidized dextran. The properties and rate of formation of the gel were related to both the amine and aldehyde levels of the precursors. These levels could be readily changed by altering the reaction conditions, and allowed good control of the gel properties. Oxidation of the dextran with periodate was accompanied by chain scission and a large reduction in molecular weight. The gel showed excellent haemostatic properties and reduction of adhesions in animal models.

Australian Journal of Chemistry, 1995

Synthetic Metals, 1999

We report the properties of MEH-PPV/onium salt blends which we find to be doped by a photoinduced... more We report the properties of MEH-PPV/onium salt blends which we find to be doped by a photoinduced electron-transfer reaction on photoabsorption in the MEH-PPV. The quantum efficiency of this process is determined as a function of the incident photon energy, and compared with the corresponding photocurrent quantum efficiency. This system can be used to measure a cumulative dose of visible or high-energy radiation.

Synthetic Metals, 1997

New CF3-substituted PPV derivatives have been synthesised by Wittig-Horner polycondensation. To o... more New CF3-substituted PPV derivatives have been synthesised by Wittig-Horner polycondensation. To obtain a better understanding of the relationship between absorption and luminescence properties and structure a single crystal X-ray analysis of a model oligomer has been performed. The effect of electron withdrawing trifluoromethyl groups at vinylidene linkages in PPVs on absorption, luminescence, hole blocking and electron injecting properties has been investigated.

Synthetic Metals, 1996

We report the use of α-sexithiophene (T6) thin films sublimed onto glass substrates coated with i... more We report the use of α-sexithiophene (T6) thin films sublimed onto glass substrates coated with indium-tin oxide in light-emitting diodes. Absolute photoluminescence quantum efficiencies were found to be in the range 10−2–10−3%, and indicate that T6 should be used as a hole injector into an emissive layer, rather than as a luminescent layer. We have fabricated double-layer organic light-emitting diodes where a cyano-substituted derivative of poly(p-phenylenevinylene) (PPV), MEH-CN-PPV, was spun on top of the T6 layer prior to evaporation of Ca-Al cathodes. Turn-on voltages for electroluminescence of about 3 V were found in structures with total thickness between 160 and 230 nm, while internal quantum efficiencies were up to 0.4%, i.e. at least ten times less than those measured in comparative devices where a PPV hole-injecting layer was used in place of T6. The substantial difference is interpreted on the basis of a significant lowering of the barrier to electron ejection from the luminescent layer into the hole-injecting layer when passing from PPV to T6. This allows inefficient recombination to take place in T6, as confirmed by the electroluminescence spectra.

Journal of Biomedical Materials Research Part A, 2014

In developing a chitosan/dextran-based (CD) hydrogel as an adhesion prevention postsurgical aid, ... more In developing a chitosan/dextran-based (CD) hydrogel as an adhesion prevention postsurgical aid, the in vivo biodegradation rate, biodistribution, and inflammatory response are important parameters to the biomedical device design. Herein, for the first time, a CD hydrogel was prepared by mixing aqueous solutions of a near infrared (NIR) labeled succinylated chitosan (SC) and tritiated [(3) H] oxidized dextran (DA). The biodegradation and biodistribution of the NIR/[(3) H]-CD hydrogel was tracked noninvasively using NIR fluorescence imaging, and by liquid scintillation counting (LSC) of organs/tissues after subcutaneous injection in BALB/c mice. The inflammatory response was assessed by measuring serum cytokine levels using a Bio-plex assay and by histological examination of injection site tissue. Fluorescence imaging showed the hydrogel to degrade in under a week. LSC revealed the hydrogel to reside mainly at the injection site, and excreted primarily via the urine within the first 48 h. The CD hydrogel showed a mild inflammatory response as cytokine levels were comparable to saline injected controls. Histological examination of injection site tissue confirmed the cytokine results. In summary, the CD hydrogel's in vivo biodegradation rate, biodistribution, and inflammatory response was determined. Our results indicate that the CD hydrogel has an appropriate biocompatibility after s.c. administration. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2014.

Synthetic Metals, 1999

A new 2,3-dibutoxy-l,4-phenylene vinylene is reported with high photoluminescence (40%) and elect... more A new 2,3-dibutoxy-l,4-phenylene vinylene is reported with high photoluminescence (40%) and electroluminescence efficiencies. The unusual substitution pattern is effective in tuning the emission colour as the polymer exhibits unexpected blueshifted emission to the green region. Crystal structures of model oligomers (PL efficiencies 80%) and theoretical calculations on optimised geometry offer insight into these interesting properties.

Synthetic Metals, 2000

We report on the characterisation of the second order nonlinear optical properties of a semiflexi... more We report on the characterisation of the second order nonlinear optical properties of a semiflexible main chain random copolymer with a head to tail structure synthesised from 4-carboxy-4′-[N-(11-hydroxyundecyl)-N-methylamino]-azobenzene and hydroxybenzoic acid. This polymer exhibits a nematic liquid crystal mesophase with a nematic-isotropic transition temperature of 200°C. We find a complicated phase behaviour for the polymer and show that the polymer films be readily annealed into large homogeneously aligned monodomains in device configurations. We have carried out measurements of the field dependent poling behaviour by means of an ellipsometric set-up after Teng and Man. We find three distinctive field regions corresponding to different mechanisms in the response of the polymer chains. No saturation in the poling response can be detected for fields up to 108 V/m. Absolute values for χ(2) reach 80 pm/V. We analysed any potential χ(3) contribution to the total NLO signal and showed that this contribution can be neglected for our measurements.

Solid-state Electronics, 1996

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be... more Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics, both as electroluminescent diodes and also as photoconductive diodes. We discuss the present understanding of the operation of light-emitting diodes which use conjugated polymers for both charge transport and emission. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and thus, bring about electron-hole capture to generate excitons at this interface. The nature of these diodes allows fabrication of microcavity structures in which the emission characteristics of the polymer are strongly modified by the allowed cavity modes. This can be used to control the colour of emission and sharpness of the emission bands.

Synthetic Metals, 1999

A new series of porphyrin-containing PPV-copolymers have been synthesised. The porphyrin units ar... more A new series of porphyrin-containing PPV-copolymers have been synthesised. The porphyrin units are attached as a side group on the main chain, in an effort to attempt to control aggregation and consequent fluorescence quenching. Emission is red-shifted from that expected in dialkoxy-PPVs owing to an efficient exciton transfer to the fluorescent porphyrin unit, leading to a more useful red colour for RGB displays. The effects of the porphyrin concentration on the PL efficiencies will be reported.

Australian Journal of Chemistry, 1990

Synthetic Metals, 1999

Liquid crystalline phthalocyanines (Pc's) are promising materials for opto-electronic application... more Liquid crystalline phthalocyanines (Pc's) are promising materials for opto-electronic applications (e.g. solar cells, electrophotography) due to their high absorption coefficients in the long wavelength region of the optical spectrum and high charge carrier mobilities in the columnar mesophase. We report here the synthesis and properties, in particular the thermotropic phase behaviour, of a series of new octakis(alkylthio)-substituted pc's.

Synthetic Communications, 1990

Feist-Benary condensations to form furans are usually carried out by reacting an á-halo aldehyde ... more Feist-Benary condensations to form furans are usually carried out by reacting an á-halo aldehyde and a β-keto ester under basic conditions. However, yields are often poor, and the main product is often a dihydrofuranol requiring subsequent acid-catalysed dehydration to form the furan. The α-halo acetaldehyde is also difficult to prepare free of water when anhydrous reaction conditions are desired.

Molecular Simulation, 2005

Synthetic Metals, 1996

Results are presented which explore the synthesis, characterization and photoluminescence of new ... more Results are presented which explore the synthesis, characterization and photoluminescence of new types of conjugated copolymers which incorporate fused thiophene units. Such materials possess intense purple-red colours and some absorb in the near-infrared. The redox processes showed that the polymers were both p- and n-dopable.

Synthetic Metals, 1999

A range of onium salts were blended with conjugated polymers and exposed to visible light. Photoi... more A range of onium salts were blended with conjugated polymers and exposed to visible light. Photoinduced doping occurred with iodonium salts, but not with sulfonium salts. Cyclic voltammetry was used to study the reaction process. This loss of photoreaction holds promise for use in sensors and radiation detectors.

Synthetic Metals, 1996

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be... more Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics both as electroluminescent diodes and as photoconductive diodes. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and, thus, bring about electron-hole capture to generate excitons at this interface. We present results on the photophysical properties of the cyanosubstituted poly(phenylenevinylene)s which provide electron transport layers if these heterostructure devices; we find evidence for strong interchain interactions (excimer formation) for the neutral excited states in these polymers, with strong red shifts of the luminescence, though preserving high photoluminescence efficiencies.

Synthetic Metals, 1994

A new poly(phenylene-co-dialkoxyphenylene) derivative was synthesized by the Suzuki coupling of a... more A new poly(phenylene-co-dialkoxyphenylene) derivative was synthesized by the Suzuki coupling of aromatic bromoboronic acids. This showed strong violet photoluminescence (peak 415 nm) in the solid state and good solubility in organic solvents. A multilayer light-emitting diode was constructed with the structure indium-tin oxide/poly(p-phenylenevinylene)/polyphenylene/calcium. Efficient light emission was observed with a peak maximum in the blue region of the visible spectrum.

Chemistry-a European Journal, 1997

The early stages of rnetal/polymer interface formation between aluminum and poly (2,5,2',5'-tetra... more The early stages of rnetal/polymer interface formation between aluminum and poly (2,5,2',5'-tetrahexyloxy-8,7'-dicyanodi-~-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction. Fax: Int. code +(65)37-3366 (0 VCH Vrrlag~gerellschaff mhH 0-69451 Wernhrrm, l Y Y 7 OY47-653U/Y7/0302-0286.R I5 00+ 25/0 Chrm Eur J 1997, 3, No 2

Macromolecules, 2000

ABSTRACT We report the synthesis and electroluminescent properties of random poly(phenylenevinyle... more ABSTRACT We report the synthesis and electroluminescent properties of random poly(phenylenevinylene) copolymers, carrying fluorine substitutions. In particular, we used 2,3,5,6-tetrafluoro-1,4-phenylenevinylene and 2-methoxy-5-(2‘-ethylhexyloxy)-1,4-phenylenevinylene moieties. The ratios of the two copolymer units were varied between 5:95 and 27:75. Electrochemical measurements showed an increase of the oxidation and a decrease of the reduction potentials of the copolymers upon increase of the fluorine content, as expected for the electron withdrawing effect of fluorine on the conjugated π-electron system. The copolymers showed emission in the red-orange region, with maximum photoluminescence efficiencies of 6.7%. We also observed lower turn-on voltages and higher electroluminescence efficiencies for lower fluorine contents.

Macromolecular Symposia, 2009

A series of hydrogels were formed from the reaction between an amine functionalized succinyl chit... more A series of hydrogels were formed from the reaction between an amine functionalized succinyl chitosan and an oxidized dextran. The properties and rate of formation of the gel were related to both the amine and aldehyde levels of the precursors. These levels could be readily changed by altering the reaction conditions, and allowed good control of the gel properties. Oxidation of the dextran with periodate was accompanied by chain scission and a large reduction in molecular weight. The gel showed excellent haemostatic properties and reduction of adhesions in animal models.

Australian Journal of Chemistry, 1995

Synthetic Metals, 1999

We report the properties of MEH-PPV/onium salt blends which we find to be doped by a photoinduced... more We report the properties of MEH-PPV/onium salt blends which we find to be doped by a photoinduced electron-transfer reaction on photoabsorption in the MEH-PPV. The quantum efficiency of this process is determined as a function of the incident photon energy, and compared with the corresponding photocurrent quantum efficiency. This system can be used to measure a cumulative dose of visible or high-energy radiation.

Synthetic Metals, 1997

New CF3-substituted PPV derivatives have been synthesised by Wittig-Horner polycondensation. To o... more New CF3-substituted PPV derivatives have been synthesised by Wittig-Horner polycondensation. To obtain a better understanding of the relationship between absorption and luminescence properties and structure a single crystal X-ray analysis of a model oligomer has been performed. The effect of electron withdrawing trifluoromethyl groups at vinylidene linkages in PPVs on absorption, luminescence, hole blocking and electron injecting properties has been investigated.

Synthetic Metals, 1996

We report the use of α-sexithiophene (T6) thin films sublimed onto glass substrates coated with i... more We report the use of α-sexithiophene (T6) thin films sublimed onto glass substrates coated with indium-tin oxide in light-emitting diodes. Absolute photoluminescence quantum efficiencies were found to be in the range 10−2–10−3%, and indicate that T6 should be used as a hole injector into an emissive layer, rather than as a luminescent layer. We have fabricated double-layer organic light-emitting diodes where a cyano-substituted derivative of poly(p-phenylenevinylene) (PPV), MEH-CN-PPV, was spun on top of the T6 layer prior to evaporation of Ca-Al cathodes. Turn-on voltages for electroluminescence of about 3 V were found in structures with total thickness between 160 and 230 nm, while internal quantum efficiencies were up to 0.4%, i.e. at least ten times less than those measured in comparative devices where a PPV hole-injecting layer was used in place of T6. The substantial difference is interpreted on the basis of a significant lowering of the barrier to electron ejection from the luminescent layer into the hole-injecting layer when passing from PPV to T6. This allows inefficient recombination to take place in T6, as confirmed by the electroluminescence spectra.