S.C. Moratti | University of Otago (original) (raw)

Papers by S.C. Moratti

Research paper thumbnail of Synthesis and Characterization of Chitosan/ Dextran-Based Hydrogels for Surgical Use

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.

Research paper thumbnail of ChemInform Abstract: Synthesis of a Novel Diterpenoid Rearrangement Product

Cheminform, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of 1,2-Dibromoethyl Acetate, a Reagent for Feist-Benary Condensations

Synthetic Communications, 1990

Research paper thumbnail of 1,2-Dibromoethyl Acetate, a Reagent for Feist-Benary Condensations

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conversion of Manoyl Oxide into 12β-Hydroxymanoyl Oxide

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conversion of 2-Oxomanoyl Oxide into an Analogue of Pisiferic Acid

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Electronic excitations in luminescent conjugated polymers

Solid State Communications, 1997

We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emi... more We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved and single-layer EL diodes achieve luminous efficiencies above 2 Lumen W -1 and peak brightnesses up to 90 000 cd m -2. We discuss measurements of photoconductivity, photovoltaic response, photoluminescence excitation spectra and stimulated emission in films of PPV. We consider that the photoexcited state in these films of PPV is the intrachain singlet exciton. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments and can be used as the active lasing medium when incorporated in suitable microcavity structures.

Research paper thumbnail of Efficient light-emitting diodes based on polymers with high electronaffinities

Research paper thumbnail of Dye-based donor/acceptor solar cells

Solar Energy Materials and Solar Cells, 2000

We have fabricated organic donor/acceptor solar cells with three different architectures using so... more We have fabricated organic donor/acceptor solar cells with three different architectures using soluble derivatives (dyes) of the molecular semiconductors phthalocyanine as electron donor (D), i.e. hole transport material and perylene as electron acceptor (A), i.e. electron transport material. These architectures comprise a blend and a double layer structure as well as the only recently reported laminated-device structure. The organic semiconducting

Research paper thumbnail of Electronic Processes of Conjugated Polymers in Semiconductor Device Structures

Synthetic Metals, 1997

We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emi... more We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved, and single-layer EL diodes achieve luminous efficiencies above 2 Lumens/W and peak brightnesses up to 90,000 cd/m2. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments, and can be used as the active lasing medium when incorporated in suitable microcavity structures.

Research paper thumbnail of Light-emitting electrochemical cells based on poly( p-phenylene vinylene) copolymers with ion-transporting side groups

Synthetic Metals, 2001

Solid-state light-emitting devices have been fabricated from blends of lithium salt/18-crown-6 et... more Solid-state light-emitting devices have been fabricated from blends of lithium salt/18-crown-6 ether complex with a ruthenium(II) binuclear complex containing 1,6-bis[4-(4 0 -methyl-2,2 0 -bipyridyl)]hexane and regular 2,2 0 -bipyridine ligands. Orange light is emitted for low turn-on voltages, i.e. ranging from 2.5 to 3 V. The use of an additional PEDOT-PSS layer, obtained from an aqueous dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS), on the indium tin oxide (ITO) anode has been investigated leading to improved operating lifetimes. By replacing the triflate salt by a derivative of a more delocalized anion, such as trifluorosulfonimide, turn-on rate is enhanced and the corresponding ionic conductivity allows to reach operating voltages in the neighborhood of the electrochemical gap of the Ru-based complex. However, whatever the case, device performances decrease upon operation within few hours. We report that the main degradation process involved in the decrease of the light emission intensity during device operation is based on an electrochemical degradation of the ruthenium complex, mainly a loss of capacity on the reduction side. #

Research paper thumbnail of Second order nonlinear optical response of nematic liquid crystalline main chain polymers

Synthetic Metals, 1999

We have synthesised and carried out preliminary characterisation of NLO-active semiflexible main ... more We have synthesised and carried out preliminary characterisation of NLO-active semiflexible main chain polymers with a head-to-tail structure which exhibit a nematic liquid crystalline mesophase. We predict that the nematic order facilitates a large number of dipoles to couple collectively to a dc~ poling field, From this process we ex attribute a slow response to a poling field and subsequent relaxation to hairpin diffusion a ong the polymer chains. Values of P ect an enhanced x@) response. We ru-r,3 of 50 pm/V were observed.

Research paper thumbnail of Efficient photodiodes from interpenetrating polymer networks

Nature, 1995

THE photovoltaic effect involves the production of electrons and holes in a semiconductor device ... more THE photovoltaic effect involves the production of electrons and holes in a semiconductor device under illumination, and their subsequent collection at opposite electrodes. In many inorganic semiconductors, photon absorption produces free electrons and holes directly 1 . But in ...

Research paper thumbnail of Photoinduced doping in conjugated polymers

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.

Research paper thumbnail of Electrochemical and optical studies of PPV derivatives and poly(aromatic oxadiazoles

Synthetic Metals, 1997

The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol The cyclic voltam... more The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol (aromatic oxadiazoles) have been (aromatic oxadiazoles) have been measured on Au/Pd and IT0 substrates. The IT0 is a convenient substrate for preparing fi ms of PPV under hi measured on Au/Pd and IT0 substrates. The IT0 is a convenient substrate for preparing fi ms of PPV under hi 7 7 and vacuum. Furthermore the CV data obtained with polymer films on IT0 more closely resemble the working E and vacuum. Furthermore the CV data obtained with polymer films on IT0 more closely resemble the working E & & h temperature h temperature device. device.

Research paper thumbnail of Liquid crystalline phthalocyanines in organic solar cells

Synthetic Metals, 1999

Small exciton diffusion lengths, insufficient charge transport and low absorption prevent organic... more Small exciton diffusion lengths, insufficient charge transport and low absorption prevent organic materials from achieving commercially useful power conversion efficiencies. The recently reported long exciton diffusion range along the columnar axes in the mesophase of disc shaped liquid crystals might represent a way to circumvent these limitations. In this paper we investigate a double-layer photovoltaic device comprising a discotic phthalocyanine derivative as electron-donor and a perylene derivative as electron-acceptor material. We fabricated one device with a pristine phthalocyanine layer and compare it with a device that was thermally treated to obtain a higher ordered mesophase.

Research paper thumbnail of The effect of X-ray irradiation on poly( p-phenylene vinylene) and derivatives

Synthetic Metals, 1997

We have studied the effect of X-ray exposure on poly(p-phenylene vinylene), PPV, and an iodo-deri... more We have studied the effect of X-ray exposure on poly(p-phenylene vinylene), PPV, and an iodo-derivative of PPV, poly(2-iodo-1,4phenylene vinylene), PIPV. We report the effect of the chemical changes produced on the optical absorption (bleaching), photoluminescence (quenching), electrical conductivity (enhancement), and field-effect mobility (enhancement). We attribute these changes in part to p-type doping of these polymers caused by the radiation exposure. These effects are enhanced for the iodo-PPV which has an increased X-ray absorption cross section and the possibility of iodine doping after C-I bond scission.

Research paper thumbnail of Site-selective fluorescence studies of poly(p-phenylene vinylene) and its derivatives

Physical Review B, 1996

We report fluorescence measurements on poly(p-phenylene vinylene), PPV, and four derivatives of t... more We report fluorescence measurements on poly(p-phenylene vinylene), PPV, and four derivatives of this polymer, all of which show strong luminescence and can be used as emissive materials in electroluminescent diodes. We measure the variation of the emission spectrum with excitation energy at low temperature, and find a threshold energy above which emission is independent of excitation energy and below which the emission energy tracks with the excitation energy. This information makes it possible to separate out the effects of spectral diffusion by exciton migration from other forms of excited-state relaxation. We find that PPV and two derivatives with asymmetric, branches side chains show little or no excited-state relaxation. In contrast, the other two derivatives (one with bromine and dodecyloxy attachments at the two and five positions on the phenylene, the other with hexyloxy attachments at these sites, and cyano groups at the vinylic carbons) show further relaxation by about 0.25 eV. We consider that emission in these two polymers is from an interchain excimer excited state. Supporting evidence for the cyano-PPV is seen in the differences between the dilute solution and solid-state fluorescence spectra.

Research paper thumbnail of Light-emitting devices based on a poly(p-phenylene vinylene) derivative with ion-coordinating side groups

We report the phase-separation and the optoelectronic properties of an alternating poly͑p-phenyle... more We report the phase-separation and the optoelectronic properties of an alternating poly͑p-phenylene vinylene͒-based copolymer, to which poly͑ethylene oxide͒, PEO, and or lithium triflate are added. The alternating units of this copolymer ͑DB-BTEM-PPV͒ are 2,3-dibutoxy-1,4-phenylene vinylene, and 2,5-bis͑triethoxymethoxy͒-1,4-phenylene vinylene, a moiety containing side groups allowing ion solvation and transport. Upon addition of the ion-transporting polymer PEO to DB-BTEM-PPV blended with lithium triflate, we have found a sizeable efficiency increase ͑from 0.9 to 1.5 cd/A͒, with a concomitant increase of the response time. We propose that this is due to solvation and complexation of lithium triflate by the PEO, which simultaneously reduces the quenching of photoluminescence ͑and electroluminescence͒ efficiency by the ionic charge, and the effectiveness of formation of highly doped, low-barrier, polymer/electrode interfaces. We discuss charge transport and injection in the copolymer and in the blend with reference to the diodes characteristics, and to the phase separation of PEO, which we investigated with atomic force microscopy.

Research paper thumbnail of Site-selective fluorescence studies of poly(p-phenylene vinylene) and its derivatives

Physical Review B, 1996

We report fluorescence measurements on poly(p-phenylene vinylene͒, PPV, and four derivatives of t... more We report fluorescence measurements on poly(p-phenylene vinylene͒, PPV, and four derivatives of this polymer, all of which show strong luminescence and can be used as emissive materials in electroluminescent diodes. We measure the variation of the emission spectrum with excitation energy at low temperature, and find a threshold energy above which emission is independent of excitation energy and below which the emission energy tracks with the excitation energy. This information makes it possible to separate out the effects of spectral diffusion by exciton migration from other forms of excited-state relaxation. We find that PPV and two derivatives with asymmetric, branches side chains show little or no excited-state relaxation. In contrast, the other two derivatives ͑one with bromine and dodecyloxy attachments at the two and five positions on the phenylene, the other with hexyloxy attachments at these sites, and cyano groups at the vinylic carbons͒ show further relaxation by about 0.25 eV. We consider that emission in these two polymers is from an interchain excimer excited state. Supporting evidence for the cyano-PPV is seen in the differences between the dilute solution and solid-state fluorescence spectra.

Research paper thumbnail of Synthesis and Characterization of Chitosan/ Dextran-Based Hydrogels for Surgical Use

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.

Research paper thumbnail of ChemInform Abstract: Synthesis of a Novel Diterpenoid Rearrangement Product

Cheminform, 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of 1,2-Dibromoethyl Acetate, a Reagent for Feist-Benary Condensations

Synthetic Communications, 1990

Research paper thumbnail of 1,2-Dibromoethyl Acetate, a Reagent for Feist-Benary Condensations

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conversion of Manoyl Oxide into 12β-Hydroxymanoyl Oxide

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Conversion of 2-Oxomanoyl Oxide into an Analogue of Pisiferic Acid

Cheminform, 1991

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Research paper thumbnail of Electronic excitations in luminescent conjugated polymers

Solid State Communications, 1997

We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emi... more We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved and single-layer EL diodes achieve luminous efficiencies above 2 Lumen W -1 and peak brightnesses up to 90 000 cd m -2. We discuss measurements of photoconductivity, photovoltaic response, photoluminescence excitation spectra and stimulated emission in films of PPV. We consider that the photoexcited state in these films of PPV is the intrachain singlet exciton. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments and can be used as the active lasing medium when incorporated in suitable microcavity structures.

Research paper thumbnail of Efficient light-emitting diodes based on polymers with high electronaffinities

Research paper thumbnail of Dye-based donor/acceptor solar cells

Solar Energy Materials and Solar Cells, 2000

We have fabricated organic donor/acceptor solar cells with three different architectures using so... more We have fabricated organic donor/acceptor solar cells with three different architectures using soluble derivatives (dyes) of the molecular semiconductors phthalocyanine as electron donor (D), i.e. hole transport material and perylene as electron acceptor (A), i.e. electron transport material. These architectures comprise a blend and a double layer structure as well as the only recently reported laminated-device structure. The organic semiconducting

Research paper thumbnail of Electronic Processes of Conjugated Polymers in Semiconductor Device Structures

Synthetic Metals, 1997

We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emi... more We report progress in the processing and application of poly(phenylene vinylene), PPV, as the emissive layer in electroluminescent diodes, LEDs. Photoluminescence efficiencies above 60% for solid films of PPV are now achieved, and single-layer EL diodes achieve luminous efficiencies above 2 Lumens/W and peak brightnesses up to 90,000 cd/m2. We demonstrate that PPV of this type can show stimulated emission in sub-picosecond pump-probe experiments, and can be used as the active lasing medium when incorporated in suitable microcavity structures.

Research paper thumbnail of Light-emitting electrochemical cells based on poly( p-phenylene vinylene) copolymers with ion-transporting side groups

Synthetic Metals, 2001

Solid-state light-emitting devices have been fabricated from blends of lithium salt/18-crown-6 et... more Solid-state light-emitting devices have been fabricated from blends of lithium salt/18-crown-6 ether complex with a ruthenium(II) binuclear complex containing 1,6-bis[4-(4 0 -methyl-2,2 0 -bipyridyl)]hexane and regular 2,2 0 -bipyridine ligands. Orange light is emitted for low turn-on voltages, i.e. ranging from 2.5 to 3 V. The use of an additional PEDOT-PSS layer, obtained from an aqueous dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS), on the indium tin oxide (ITO) anode has been investigated leading to improved operating lifetimes. By replacing the triflate salt by a derivative of a more delocalized anion, such as trifluorosulfonimide, turn-on rate is enhanced and the corresponding ionic conductivity allows to reach operating voltages in the neighborhood of the electrochemical gap of the Ru-based complex. However, whatever the case, device performances decrease upon operation within few hours. We report that the main degradation process involved in the decrease of the light emission intensity during device operation is based on an electrochemical degradation of the ruthenium complex, mainly a loss of capacity on the reduction side. #

Research paper thumbnail of Second order nonlinear optical response of nematic liquid crystalline main chain polymers

Synthetic Metals, 1999

We have synthesised and carried out preliminary characterisation of NLO-active semiflexible main ... more We have synthesised and carried out preliminary characterisation of NLO-active semiflexible main chain polymers with a head-to-tail structure which exhibit a nematic liquid crystalline mesophase. We predict that the nematic order facilitates a large number of dipoles to couple collectively to a dc~ poling field, From this process we ex attribute a slow response to a poling field and subsequent relaxation to hairpin diffusion a ong the polymer chains. Values of P ect an enhanced x@) response. We ru-r,3 of 50 pm/V were observed.

Research paper thumbnail of Efficient photodiodes from interpenetrating polymer networks

Nature, 1995

THE photovoltaic effect involves the production of electrons and holes in a semiconductor device ... more THE photovoltaic effect involves the production of electrons and holes in a semiconductor device under illumination, and their subsequent collection at opposite electrodes. In many inorganic semiconductors, photon absorption produces free electrons and holes directly 1 . But in ...

Research paper thumbnail of Photoinduced doping in conjugated polymers

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.

Research paper thumbnail of Electrochemical and optical studies of PPV derivatives and poly(aromatic oxadiazoles

Synthetic Metals, 1997

The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol The cyclic voltam... more The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol The cyclic voltammograms and optical properties for PPV, MEH-WV, CN-PPV and pol (aromatic oxadiazoles) have been (aromatic oxadiazoles) have been measured on Au/Pd and IT0 substrates. The IT0 is a convenient substrate for preparing fi ms of PPV under hi measured on Au/Pd and IT0 substrates. The IT0 is a convenient substrate for preparing fi ms of PPV under hi 7 7 and vacuum. Furthermore the CV data obtained with polymer films on IT0 more closely resemble the working E and vacuum. Furthermore the CV data obtained with polymer films on IT0 more closely resemble the working E & & h temperature h temperature device. device.

Research paper thumbnail of Liquid crystalline phthalocyanines in organic solar cells

Synthetic Metals, 1999

Small exciton diffusion lengths, insufficient charge transport and low absorption prevent organic... more Small exciton diffusion lengths, insufficient charge transport and low absorption prevent organic materials from achieving commercially useful power conversion efficiencies. The recently reported long exciton diffusion range along the columnar axes in the mesophase of disc shaped liquid crystals might represent a way to circumvent these limitations. In this paper we investigate a double-layer photovoltaic device comprising a discotic phthalocyanine derivative as electron-donor and a perylene derivative as electron-acceptor material. We fabricated one device with a pristine phthalocyanine layer and compare it with a device that was thermally treated to obtain a higher ordered mesophase.

Research paper thumbnail of The effect of X-ray irradiation on poly( p-phenylene vinylene) and derivatives

Synthetic Metals, 1997

We have studied the effect of X-ray exposure on poly(p-phenylene vinylene), PPV, and an iodo-deri... more We have studied the effect of X-ray exposure on poly(p-phenylene vinylene), PPV, and an iodo-derivative of PPV, poly(2-iodo-1,4phenylene vinylene), PIPV. We report the effect of the chemical changes produced on the optical absorption (bleaching), photoluminescence (quenching), electrical conductivity (enhancement), and field-effect mobility (enhancement). We attribute these changes in part to p-type doping of these polymers caused by the radiation exposure. These effects are enhanced for the iodo-PPV which has an increased X-ray absorption cross section and the possibility of iodine doping after C-I bond scission.

Research paper thumbnail of Site-selective fluorescence studies of poly(p-phenylene vinylene) and its derivatives

Physical Review B, 1996

We report fluorescence measurements on poly(p-phenylene vinylene), PPV, and four derivatives of t... more We report fluorescence measurements on poly(p-phenylene vinylene), PPV, and four derivatives of this polymer, all of which show strong luminescence and can be used as emissive materials in electroluminescent diodes. We measure the variation of the emission spectrum with excitation energy at low temperature, and find a threshold energy above which emission is independent of excitation energy and below which the emission energy tracks with the excitation energy. This information makes it possible to separate out the effects of spectral diffusion by exciton migration from other forms of excited-state relaxation. We find that PPV and two derivatives with asymmetric, branches side chains show little or no excited-state relaxation. In contrast, the other two derivatives (one with bromine and dodecyloxy attachments at the two and five positions on the phenylene, the other with hexyloxy attachments at these sites, and cyano groups at the vinylic carbons) show further relaxation by about 0.25 eV. We consider that emission in these two polymers is from an interchain excimer excited state. Supporting evidence for the cyano-PPV is seen in the differences between the dilute solution and solid-state fluorescence spectra.

Research paper thumbnail of Light-emitting devices based on a poly(p-phenylene vinylene) derivative with ion-coordinating side groups

We report the phase-separation and the optoelectronic properties of an alternating poly͑p-phenyle... more We report the phase-separation and the optoelectronic properties of an alternating poly͑p-phenylene vinylene͒-based copolymer, to which poly͑ethylene oxide͒, PEO, and or lithium triflate are added. The alternating units of this copolymer ͑DB-BTEM-PPV͒ are 2,3-dibutoxy-1,4-phenylene vinylene, and 2,5-bis͑triethoxymethoxy͒-1,4-phenylene vinylene, a moiety containing side groups allowing ion solvation and transport. Upon addition of the ion-transporting polymer PEO to DB-BTEM-PPV blended with lithium triflate, we have found a sizeable efficiency increase ͑from 0.9 to 1.5 cd/A͒, with a concomitant increase of the response time. We propose that this is due to solvation and complexation of lithium triflate by the PEO, which simultaneously reduces the quenching of photoluminescence ͑and electroluminescence͒ efficiency by the ionic charge, and the effectiveness of formation of highly doped, low-barrier, polymer/electrode interfaces. We discuss charge transport and injection in the copolymer and in the blend with reference to the diodes characteristics, and to the phase separation of PEO, which we investigated with atomic force microscopy.

Research paper thumbnail of Site-selective fluorescence studies of poly(p-phenylene vinylene) and its derivatives

Physical Review B, 1996

We report fluorescence measurements on poly(p-phenylene vinylene͒, PPV, and four derivatives of t... more We report fluorescence measurements on poly(p-phenylene vinylene͒, PPV, and four derivatives of this polymer, all of which show strong luminescence and can be used as emissive materials in electroluminescent diodes. We measure the variation of the emission spectrum with excitation energy at low temperature, and find a threshold energy above which emission is independent of excitation energy and below which the emission energy tracks with the excitation energy. This information makes it possible to separate out the effects of spectral diffusion by exciton migration from other forms of excited-state relaxation. We find that PPV and two derivatives with asymmetric, branches side chains show little or no excited-state relaxation. In contrast, the other two derivatives ͑one with bromine and dodecyloxy attachments at the two and five positions on the phenylene, the other with hexyloxy attachments at these sites, and cyano groups at the vinylic carbons͒ show further relaxation by about 0.25 eV. We consider that emission in these two polymers is from an interchain excimer excited state. Supporting evidence for the cyano-PPV is seen in the differences between the dilute solution and solid-state fluorescence spectra.