Search

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 10 8 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.

We present a theoretical and experimental investigation of methoxy- and cyano-substituted p-phenylenevinylene model compounds. The compound containing both the alkoxy and cyano substitution exhibits a drop in the quantum yield relative to the singly-substituted alkoxy or alkyl compounds. In addition the emission spectrum loses structure and shifts to the red. Model calculations are performed on the chromophore and ab-initio CIS calculations show that the first excited state HOMO to LUMO transition is delocalised in methoxy-substituted compounds and localised on methoxy- and cyano-substituted compounds.

Time-resolved and steady-state photoluminescence (PL) studies of a cyano-substituted poly(phenylene vinylene) (CNPPV) in toluene solution are reported as a function of temperature. On reducing temperature there is no evidence for the formation of aggregates, with both the absorption and emission properties revealing only a moderate increase in the average length of conjugation. Time-resolved anisotropy data reveal a single rotational correlation time of six nanoseconds. These data are consistent with a very low molecular weight polymer sample that behaves in a molecular fashion.

We present the optical properties of four poly(p-phenylenevinylene) (PPV)-based statistical copolymers, which combine monomers of highly luminescent polymers and monomers carrying crown ether side groups. The photoluminescence efficiency for films on spectrosil ranges from 28% to 52%, whereas the electroluminescence (EL) efficiency of single-layer diodes with Al cathodes reaches 0.6 cd/A (internal quantum efficiency of 1.4%). Surprisingly, the efficiency for Ca cathodes diodes is lower than for Al ones. Slight variation of the EL spectra from pixel to pixel affects all the copolymers of the family, and we consider that it is indicative of chain aggregation induced by the crown ether moieties. Studies of light-emitting electrochemical cells, LECs, based on one of these polymers show that the ion mobility induced by the presence of the crown ethers is relatively small. Typical LEC behaviour was observed upon addition of poly(ethylene oxide), with EL internal quantum efficiency reaching 2.3%.

We report the fabrication of blue-emitting organic LEDs based on a soluble poly(p-phenylenevinylene) (PPV) copolymer, which takes advantage of both meta linkages and of an unusual substitution pattern (2,3) of the solubilising alkoxy chains onto the aromatic ring, in order to blue-shift the radiative emission. We recorded turn-on fields of similar to 1.1 MV/cm and efficiencies up to 0.032 ed/A in sandwich structures utilising Ca cathodes and a plasma-treated indium tin oxide (ITO) anode, coated with a poly(3,4-ethylene dioxythiophene) transport layer. The 1931 Commission Internationale de L'Eclairage (CIE) coordinates of the electroluminescence spectrum are (0.1881, 0.1812) without any filtering and (0.137, 0.0666), i.e., suitable for full colour displays applications, after filtering away the emission extending beyond 510 nm. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

We report some steady-state and time-resolved photoluminescence (PL) studies of a cyano-substituted phenlyene vinylene polymer film as a function of temperature. In contrast to simple aromatic molecules, on reducing the temperature the luminescence spectrum drops in intensity, gains structure and shifts to lower energy. While the rate of decay of the PL increases at short wavelengths and remains almost constant at long wavelengths. Using a simple kinetic scheme involving an intra-chain and an inter-chain excitation, we have successfully explained these data in terms of a delayed luminescence model.

We report investigations on a 4-acetamido-substituted naphthalimide polymer (4-AcNI) as a component for light-emitting diodes (LEDs). Devices prepared with 4-AcNI as the active material are relatively inefficient (4 × 10−4%). Higher internal quantum efficiency values of 0.4% are achieved if 4-AcNI is used as an electron-transporting layer (ETL) in devices which use poly(p-phenylene vinylene) (PPV) as a hole transport layer. For Al cathodes, this material proves to be superior to similar devices which use 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as the ETL. The results are used to shed some light on the function of ETLs in organic LEDs.

Recent results are reported on the synthesis of statistical copolymers 8 and 9 derived from the highly luminescent silyl PPV derivative (DMOS-PPV) with various alternative building blocks carrying side chains capable of supporting polyelectrolytes. These polymers are prepared by Gilch dehydrohalogenation polymerization. It is of interest to study the effect on charge transport in standard electroluminescent (EL) devices using these PPV copolymers. Moderately efficient conventional single-layer devices are obtained for copolymer 9 . When fabricated in a light-emitting electrochemical cell (LEC) configuration (lithium triflate) without any extra supporting polymer electrolyte (e.g., poly(ethylene oxide), PEO), devices based on both 8 and 9 show lower turn-on voltages and improved efficiency.

We report some time-resolved luminescence measurements on the conjugated polymer, MEH-PPV, that show a marked dependence on the intensity of the excitation light. At low laser powers the excited state lifetime is longer than has been reported previously and is consistent with emission from an interchain excitation that has low oscillator strength and hence a long natural radiative lifetime. We rationalise these data with a simple scheme that summarises the excited state kinetics in this and other conjugated, electroluminescent polymers.

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/m 2 . 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.

A novel silyl-substituted solvent processible poly(1,4-phenylenevinylene) (PPV) derivative, poly(2-dimethyloctylsily 1-1, 4phenylenevinylene) (DMOS-PPV) and copolymers of DMOS-PPV and poly(2-methoxy-5-ethylhexyloxy-1,4-phenylenevinylene) (MEH-PPV) have been synthesized by the dehydrohalogenation route, and the light-emitting properties of these polymers have been studied. Electroluminescent devices were fabricated with these polymers as emitting layers, and ITO and Al as anode and cathode, respectively. A single layer device using DMOS-PPV as the emissive layer showed 0.2 % internal quantum efficiency. Single layer devices using the copolymers showed internal quantum efficiencies between 0.1 – 0.02 % depending on the copolymer compositions.

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.

We report measurements of the photovoltaic effect in heterojunction structures consisting of a layer of C60 thermally evaporated onto a film of the conjugated polymer poly(p-phenylenevinylene) (PPV) sandwiched between electrodes of indium-tin oxide and Al. Peak quantum efficiencies of up to about 9% (electrons collected per incident photon) were measured under short-circuit conditions, with corresponding open-circuit voltages approaching 0.9 V. Increased quantum yields were obtained under forward and reverse biases. We model the response as arising from the dissociation of photogenerated excitons at the PPV/C60 interface, with electron transfer to the C60. The C60 layer acts as a dielectric spacer, providing a constructive enhancement of the optical fields at the PPV/C60 interface. We have applied this model to estimate an exciton diffusion range of 60 to 80 A.

We report measurements of the efficiency and time dependence of photoluminescence in a high electron affinity cyano-substituted derivative of poly (p-phenylenevinylene). In solution the photoluminescence quantum yield is 0.52 ± 0.05, and the luminescence lifetime is 0.9 ± 0.1 ns. In solid films the luminescence quantum yield is 0.35±0.03 and the luminescence lifetime, of 5.6 ± 0.2 ns, is much longer. These results strongly suggest that the emission from the film is from an inter-chain excitation, and that inter-molecular interactions are an important factor to consider in the design of highly luminescent conjugated polymers.

In this work we report the synthesis and characterization of processable poly(aromatic oxadiazole)s. The polymers are rendered processable by either dissolving the polymer in strongly acidic organic solvent or by the thermal conversion of a soluble precursor polyhydrazide. The optical and charge transporting properties of the polymers have been investigated by UV-Vis absorption, photoluminescence spectroscopy and cyclic voltammetry. All the polymers have been found to exhibit strong purple-blue fluorescence and good hole-blocking and electron-injecting properties.

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.

We report photoluminescence studies of poly(3-dodecylthiophene) (P3DT) in solution. In a good solvent the polymer exhibits luminescence with a high quantum efficiency and a decay time of 500 ps. In a poor solvent the emission is red shifted with a 20-fold reduction in quantum efficiency and a decay profile that is non-monoexponential, but has an average lifetime that is very similar to the good solvent environment. The data indicate a large increase in the natural radiative lifetime from approximately 1 ns in a good solvent to 20 ns in a poor solvent, which implies an emitting state that is different in the two situations. In the poor solvent the spectrum is almost identical to that of the thin film, suggesting that the polymer aggregates in the solution and the emitting species is the same in both environments. The data are consistent with the formation of an excited state that is not localized on a single chain but is delocalized over more than one chain.

We report investigations on the use of singly and doubly functionalised poly(methacrylates) (PMA) for the fabrication of polymeric light-emitting diodes (LEDs). The functional groups we used were distyrylbenzene (DSB) as blue chromophore and 2-phenyl-5-phenyl-1,3,4-oxadiazole (PPD) or 2-phenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as charge-transport groups to produce three homopolymers (with one functional group only) and a copolymer bearing both DSB and PBD groups (PMA-DSB-PBD). The polymers have been used alone or blended together in single-layer devices or in double-layer devices, for which a thin poly( p -phenylene vinylene) (PPV) layer was used as a hole-transporting material. Despite the high photoluminescence yield of these DSB-based materials, successful fabrication of blue-emitting LEDs has only been achieved by using the copolymer, both in single- and double-layer devices.

Summary form only given. A new series of alternating copolymers based on poly(p-phenylenevinylene) (PPV) was synthesized. The electron affinity of the polymers is substantially increased through the use of electron-withdrawing substituents. Optimum conditions for the condensation polymerization were explored, and polymers with a M/sub n/ in excess of 30,000 were produced. The synthesis is extremely flexible and allows a large variety of conjugated polymers with different emission properties to be synthesized. Cyclic voltammetry was used to estimate the position of the HOMO and LUMO relative to poly(2,5-dialkoxy-1,4-phenylenevinylene) analogues. Fabrication of efficient bilayer polymer LEDs using PPVin conjunction with the new polymers and stable metal negative contacts such as aluminum and gold is reported.

We consider 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 efficient electron—hole capture to generate excitons. We also report recent results on the fabrication of diodes on top of non-transparent substrates such as silicon. This requires the deposition of a transparent top electrode, and we have used indiumtin oxide in this role.

Light-emitting diodes fabricated with a layer of poly( p -phenylenevinylene) (PPV) sandwiched between electrodes of indium-tin oxide (ITO) and calcium have been studied over extended periods of operation. Different biasing conditions, with drive at constant voltage, constant current and with a.c. voltage have been used. The best results indicate that continuous operation with square-wave biasing (50% duty cycle, 1070 Hz) and current density in the range 300–800 mA/cm 2 can be achieved beyond 1200 h. This amounts to about 825 A h/cm 2 total charge flux through the device. No significant spectral aging has been detected on this time scale. Emission spectra do not change even when varying the frequency of sinusoidal excitation or the level of a d.c. bias.

We report investigations of electroluminescence and photoluminescence in several soluble ladder-type oligo( para -phenylene)s which we have used in a range of single- and double-layer electroluminescence devices. In double-layer devices which incorporate a thin film of poly(phenylenevinylene) (PPV) as a hole transport layer, yellow emission with 0.6% internal quantum efficiency can be achieved. We find that pure blue emission can be obtained by diluting the luminescent polymer into a poly(9-vinylene carbazole) (PVK) matrix. This gives a blue-emitting electroluminescent device with more than 0.1% internal quantum efficiency.

The effects of doping poly(cyanoterephthalylidene) with sodium in ultrahighvacuum been studied by optical absorption spectroscopy. Upon doping, new optical transitions are observed within the bandgap; the characteristics of these transitions are consistent with the formation of bipolarons. The optical absorption results are confirmed by direct measurements of the doping-induced gap states using ultraviolet photoelectron spectroscopy.

We report the electrochemical, optical, and electroluminescent properties of fluorine containing poly(phenylene vinylene) random copolymers. We used 2,3,5,6-tetrafluoro-1,4-phenylene vinylene and 2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene moieties, with ratios of the two copolymer units varying between 5:95 and 27:75. The electron withdrawing effect of fluorine on the conjugated π-electron system was confirmed by electrochemical measurements, which showed an increase of the oxidation and a decrease of the reduction potentials, upon increase of the fluorine content. Light emitting diodes fabricated from the copolymers showed emission in the red-orange, with lower turn-on voltages and higher electroluminescence efficiencies for lower fluorine contents. We observed maximum photoluminescence efficiencies of 6.7%.

We present the electro-optical characteristics of LECs based on two copolymers derived from poly(p-phenylene vinylene), DB-alt-BTEM-PPV and BDMOS-co-BTEM-PPV, having ion-transporting side groups. We find typical LEC behaviour upon addition of lithium triflate. Addition of poly(ethylene oxide), PEO, improves the EL efficiency, but the response time increases. We discuss these observations on the basis of PEO-induced phase separation.

A range of substituted head-to-tail polythiophene random copolymers containing alkyl and ω-hydroxyalkyl side chains has been synthesized by protection of the alcohol as a tetrahydropyranyl acetal during polymerization. The ω-hydroxyl group can be transformed into an azide which, on heating, decomposes and leads to crosslinking which renders the solid polythiophene film insoluble and modifies its optical properties. An ω-hydroxyalkyl homopolymer has also been synthesized by this route and affords polymers with unexpected optical properties.

New electroluminescent poly(arylene vinylene)s 1 containing electron-withdrawing/donating substituents have been synthesized by the precursor route outlined below. The synthesis of two novel polymers and the evaluation of their photoluminescent and electroluminescent properties in polymer light-emitting diodes (LEDs) are reported.

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.

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.

PITN is an easily prepared low band-gap conjugated polymer, albeit very insoluble. The best synthetic route is the condensation of phthalic anhydride derivatives with P 4 S 10 . We have found that the, often more convenient, phthalic acids or methyl esters can he used as readily in place of the anhydride. We have also looked at a range of new substituted PITN polymers, and copolymers. No significant band gap reduction has been observed. This work was carried out as part of Technology Group 7 of the MoD Corporate Research Programme.

We present an experimental characterisation of cyano-substituted p-phenylene vinylene model compounds and polymers. The photophysics of these samples in toluene solution are investigated using steady state and time-resolved photoluminescence spectroscopy The influence of cyano and methoxy substitution on the energetics and the natural radiative lifetime are studied.

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.

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.

We report the synthesis and luminescence properties of poly[2,5-bis(dimethyloctylsilyl)-l,4-phenylene vinylene)](BDMOS-PPV) 4 and its statistical copolymer poly[2,5-bis(dimethyloctylsilyl)-1,4-phenylene vinylene)]-co-[2,5-bis(trisethoxymethoxy)-1,4-phenylene vinylene)] (BDMOS-BTEM-PPV) 6 with units carrying ion-transporting triethoxy side-chains. The highly fluorescent polymers were synthesised by dehydrohalogenation polymerisation and show promise as materials for LED and LEC fabrication.

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.

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.

We report the effects of the substitution of butoxy chains on the phenyl 2,3 positions of poly(p-phenylene vinylene) (PPV). We find that this substitution has a remarkable influence on the optical and electroluminescent properties of the resulting semiconductor (DB-PPV) which does not show the red-shift of the emission, typical of alkoxy substituted PPVs, such as poly(2-methoxy-5-(2′-ethyl-hexyloxy)-l, 4-phenylene vinylene), MEH-PPV, dominated by the influence of the π-electron rich oxygen atom. We report photoluminescence (PL), quantum efficiencies of 40%, electroluminescence (EL) efficiencies of 0.6 cd/A in 2-layer ITO/PPV/DB-PPV/Ca diodes, and luminances up to 4500 cd/m 2 .

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.

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.

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 expect an enhanced χ (2) response. We attribute a slow response to a poling field and subsequent relaxation to hairpin diffusion along the polymer chains. Values of r 33 -r 13 of 50 pm/V were observed.

The development of improved polymers for light emitting diodes (LED)s requires fluorescent materials with high electron affinities to act both as emitters and as charge transport materials. In this paper we report the synthesis of novel distyrylpyrazines and distyrylpyrazine- N-oxides as model compounds for novel high electron affinity polymers. The UV-VIS and PL emission spectra demonstate that the emission of these materials can be tuned from blue to red by changing the substituents. Cyclic voltammetry reveals that these compounds possess high electron affinities

Several soluble precursor routes, involving sulfonium-, methoxy-, and chloro-substituted polymers, have been investigated for the synthesis of poly(pyridine vinylene)(PPyV). The thermal conversions of these precursors to fully conjugated polymer PPyV have been characterised by TGA, FT-IR and UV-VIS spectroscopy in conjunction with microanalysis. Of all the precursors, the chloro-substituted polymer is the most convenient for forming good quality thin films. PPyV fluoresces orange red and has a HOMO-LUMO band gap of 2.2 eV. PPyV has a lower luminescent quantum efficiency compared with its analogue, poly(phenylene vinylene) (PPV), but a higher electron affinity according to CV measurements (with reduction potential of -1.3 V). PPyV was used as an orange red emissive layer in a LED using aluminium as cathode.

New CF 3 -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.

We have studied the effect of X-ray exposure on poly(p-phenylene vinylene), PPV, and an iodo- derivative of PPV, poly(2-iodo-1,4-phenylene 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.

We present photocurrent measurements of poly(p-phenylene vinylene) (PPV) and derivatives for photon energies up to 5.0 eV. We observe photocurrent peaks related to the first, second and third absorption peaks, which we associate with the dissociation of a succession of increasingly energetic excitons. We have performed INDO/SCI calculations for the five-ring PPV oligomer, which show different distributions of the electronic charge of the exciton wavefunction over the chain at different excitation energies. We discuss the significance of these states for the photoconduction in PPV and question the applicability of a band-based model.

The synthesis of a new poly(methacrylate) copolymer bearing an efficient blue light emitting chromophore, a charge transporting aromatic oxadiazole and a UV-sensitive crosslinkable unit is reported. The statistical copolymer was synthesized via a multi-step route and has been characterised by NMR, FT-IR, and DSC. The copolymer has excellent solution processibility and exhibits strong luminescence. Upon cross-linking via UV-treatment, the copolymer becomes insoluble, while gaining both mechanical strength and thermal stability without loss of luminescence. The structure and properties of this novel copolymer and its application in light emitting devices are discussed.

The cyclic voltammograms and optical properties for PPV, MEH-PPV, CN-PPV and poly(aromatic oxadiazoles) have been measured on Au/Pd and ITO substrates. The ITO is a convenient substrate for preparing films of PPV under high temperature and vacuum. Furthermore the CV data obtained with polymer films on ITO more closely resemble the working EL device.

We present the photophysics of some soluble poly(3-alkyltbiophenes) (P3ATs) in fluid solution and in the solid state. We have used quantitative time-resolved and steady-state luminescence spectroscopies to examine the photophysics of these polymers in the different environments. We report data that examine the nature of the excited states in these different media and offer an alternative explanation to the low luminescence quantum efficiency of the P3AT films in terms of a decrease in the natural radiative lifetime of the emitting state. The importance of the solvating alkyl groups will be discussed in terms of the excited state dynamics, the nature of the excited states and the influence on both the solvato — and thermochromic properties of these polymers.