Synthesis and photophysics of new highly luminescent poly(alkylthiophene) derivatives with pyridine in the backbone

Starting from 2,6-bis-(3-octylthiophene-2yl)-pyridine, two new poly(alkylthiophene) derivatives, POTPyOT and POTPy, containing pyridine in the backbone were prepared from nickel(0)-mediated Stille coupling or by palladium-catalyzed Yamamoto coupling. These polymers exhibited good solubility in common organic solvents, thermal stability up to 400 °C, and facile film formation. They were amorphous and give strong luminescence both in CHCl₃ solution and solid state film. The polymers emitted blue light in solution with photoluminescence (PL) emission maximum at 420-484 nm and green light with PL emission maximum at 500-514 nm in thin films. These polymers showed a reversible redox reaction at potential from 0 to 1.3 V (vs. SCE). Nevertheless, the reduced form of the polymer was very unstable; it decomposed in the presence of oxygen or water. The emission and UV-vis absorption of the polymer were influenced by the solvent polarity, protonation, and acid-base treatment. These may be the results of the stabilization of the polar excited state by solvation and the change of the conformation in polymer backbone. Electroluminescence (EL) was achieved from a single-layer PLED with the configuration of ITO/POTPyOT/Al. The turn-on voltage of the device is 10 V and the λ_max (550 nm) of the EL is voltage independent.     

Pure color and stable blue-light emission-alternating copolymer based on fluorene and dialkoxynaphthalene

A new blue-light emitting polymer that alternates between fluorene and alkoxynaphthalene structure has been developed. The fluorene and naphthalene units were highly distorted with an angle of 76.22° according to theoretical calculations. The obtained polymer has a weight average molecular weight of 273,800 with a polydispersity index of 2.35, good solubility and high thermal stability with a T_g of 176 °C. The film photoluminescence (PL) spectrum (405 nm) is consistent with that of solution and the PL spectra of the polymer did not show any peak in the long wavelength region even after annealing for 24 h at 100 °C. The double-layered device with an ITO/PEDOT/polymer/LiF/Al structure has a turn-on voltage of about 5.4 V, maximum brightness of 110 cd/m² and an electroluminescent efficiency of 0.09 cd/A. The OLED generates pure blue EL emission (λ_max = 405 nm) with excellent CIE coordinates (x = 0.15, y = 0.10) as well as stable blue EL emission that is not altered by voltage increase.     

A novel conjugated polymer based on cyclopenta[def]phenanthrene backbone with spiro group

Poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[def]phenanthrene)) (PCPP) is a stable blue light emitting conjugated polymer even after annealing at 150 °C or operation of the device in air. The spiro form of PCPP, poly(2,6-(3′,6′-bis(2-ethylhexyloxy)-4,4′-spirobi(4H-cyclopenta[def]phenanthrene))) (spiro-PCPP), has been synthesized by Yamamoto polymerization. The PL emission spectrum of the polymer in THF solution shows a maximum peak at 398 nm, nearly identical with that of PCPP. The PL spectrum of the polymer in the solid state exhibits a maximum peak at 451 nm, which is red-shifted over 50 nm from that of the solution, due to the inter-chain interaction of the polymers. The PL spectra of spiro-PCPP in the mixture of THF and MeOH from 9:1 to 3:7 ratios showed increasing peaks at 458 and 484 nm. With an increased ratio of the hydrophilic solvent (MeOH), the inter-chain interaction of the hydrophobic polymers was enhanced to show peaks at 458 and 484 nm. This phenomenon has the same tendency as compared to the PL spectrum in solid thin film state. The polymer LED with the configuration of ITO/PEDOT/spiro-PCPP/Ca:Al emitted light with maximum peaks at around 463 nm. The emission color of the spiro-PCPP device is sky blue with the CIE coordinates of (0.14, 0.15), which are close to those of the standard blue (0.14, 0.08).     

Synthesis and properties of various PPV derivatives with phenyl substituents

New electroluminescent polymers with various phenyl groups, poly[2-dimethyl(octyl)silyl-5-(4-(dimethyl(octyl)silyl)phenyl)-1,4-phenylenevinylene] (P1), poly[2,5-bis(4-(dimethyl(octyl)silyl)phenyl)-1,4-phenylenevinylene] (P2), poly[2,5-bis(9,9-dihexylfluorenyl)-1,4-phenylenevinylene] (P3), and poly[2,5-bis(4-(4-(2-etylhexyloxy)phenyl)phenyl)-1,4-phenylenevinylene] (P4), have been synthesized by the Gilch polymerization. The maximum absorption peaks of P1-P4 appeared at 388-423 nm in THF solution, and are red-shifted to 404-425 nm in solid thin film. The photoluminescence (PL) emission spectra of P1-P4 show a maximum peak at 482-503 nm in THF solution and at 521-549 nm as the solid film state. The emission spectra in the solid film state are more red-shifted over 40 nm, and the full width at half maximum (fwhm) was 30 nm greater than the solution conditions. The polymer light-emitting diodes (PLEDs) with the configuration of ITO/PEDOT/polymer/Al emitted light with maximum peaks at around 517-546 nm. The various phenyl substituents, with intermolecular interactions in the solid film state, can introduce the color tuning and device performance enhancement of the conjugated polymer as an emissive layer in PLED.     

Efficient and color pure blue light emitting random copolymer with fluorene and fluorenylstilbene

A blue electroluminescent polymer, random copolymer of fluorenylstilbene and fluorene, was prepared by the nickel catalyzed coupling reaction. The structure and properties of the copolymer were analyzed by various spectroscopic methods. The obtained polymer had good solubility and thermal stability with high T_g. The polymer in thin film emits strong blue luminance (max=468 nm) with narrow bandwidth upon photoexcitation. PL spectrum of the polymer in the film is almost consistent with that of solution one as well as the EL spectrum, indicating that the aggregation and the excimer fluorescence are suppressed by the introduction of fluorenylstilbene comonomer. Moreover, the introduction of fluorenylstilbene comonomer lowered the oxidation potential to lead feasible hole injection, when the compared with poly(fluorene) homopolymer. The ITO/PEDOT/polymer/LiF/Al device showed the maximum brightness of 3500 cd/m² with a turn on voltage of 4.4, the maximum efficiency of 0.878 lm/W and blue emission with CIE chromaticity coordinates of ((x,y)=(0.17, 0.25)).     

Enhancing the electroluminescence properties of novel blue light emitting polymer and MEH‐PPV based white light emitting polymer devices by processing condition optimization

A series of triarylaminooxadiazole‐containing tetraphenylsilane light emitting polymer (PTOA) and poly(2‐methoxy, 5‐(2′‐ethyl‐hexyloxy)‐p‐phenylene‐vinylene) (MEH‐PPV) based white light emitting polymer devices (PLEDs) were fabricated to study blue and orange–red emitter composition and light emitting layer processing effects on white emission electroluminescence properties. Color purity, current turn‐on voltage, brightness, and current efficiency were strongly determined by MEH‐PPV content and the thin film processing condition. The intensity of PTOA blue emission was equal to that of MEH‐PPV orange–red emission when the device was fabricated by a polymer composite film containing 10 wt % of MEH‐PPV. Color purity [Commission Internationale de L'Eclairage (CIE_x,y) coordinates (0.26,0.33)] was nearly white emission under applied 8 V. The brightness and current efficiency of PTOA‐MEH‐PPV composite film based devices increased as MEH‐PPV content increased. Furthermore, white emission blue shifted with increasing spin‐rate of thin film coating and applied voltage. Low turn‐on voltage, high current density, and high brightness were obtained for the device fabricating with light emitting layer coating with high spin‐rate. Moreover, low current efficiency was obtained for the PLED with a thinner light‐emitting layer. A white emission CIE (0.28,0.34) was obtained for PTOA‐MEH‐PPV based white PLED. White PLED brightness and efficiency can be as high as 700 cd/m² and 0.78 cd/A, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Enhancing the electroluminescence performances of blue polymer light emitting devices via carriers transporting materials incorporation

A series of polymer light emitting devices (PLEDs) based on the composite films of N‐arylbenzimidazoles trimer (TPBI), poly (n‐vinylcarbazole) (PVK), and a triarylaminooxadiazole‐containing tetraphenylsilane light emitting polymer (PTOA) were investigated. Electroluminescence (EL) performance is enhanced with doped TPBI into the light‐emitting layer for the PTOA‐based devices. A deep blue emission (Commission Internationale de L'Eclairage (CIE_x,y) corodinates (0.16,0.06)) is obtained for the TPBI‐PTOA‐based device. Brightness and current efficiency of the TPBI‐PTOA‐based device can be as high as 961 cd/m² and 1.85 cd/A, respectively. The EL performances of TPBI‐PTOA composite film‐based devices are further enhanced by inserting a TPBI layer into the light emitting layer and cathode interface for a better electron and hole charge balance. Doping TPBI into the light‐emitting layer of PVK‐PTOA is not favorable for enhanced EL performances. Brightness and current efficiency reduced with increasing TPBI content for the TPBI‐PVK‐PTOA‐based devices. Similar results are obtained for devices based on the TPBI‐PVK‐PTOA/TPBI bi‐layer composite solid film. Morphology and charge balance effects on EL performances of TPBI‐PTOA and TPBI‐PVK‐PTOA composite films based PLEDs are discussed in detail. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The influence of tetrakis-ethylhexyloxy groups substituted in PPV derivative for PLEDs

New electroluminescent polymer with tetrakis-alkoxy group, poly[2,3,5,6-tetrakis(2-ethylhexyloxy)-1,4-phenylenevinylene] (TEH-PPV), has been synthesized by the Gilch polymerization. In solid film state, the TEH-PPV exhibits absorption spectra with maximum peaks at 451 nm, and PL spectrum at 505-545 nm. As compared to MEH-PPV, TEH-PPV with tetrakis-ethylhexyloxy groups in phenylene unit can get shorter conjugation length, and had more blue shifted absorption and emission peaks due to steric hindrance, in spite of increasing the number of alkoxy substituents which may increase the effective conjugation length caused by the electron-donating effect. The polymer LEDs (ITO/PEDOT/polymer/Al) of TEH-PPV showed emission with maximum peaks at around 505-590 nm. Tetrakis-ethylhexyloxy groups induced very typical vibronically structured band in solid film state, since the conjugated backbone is twisted by steric hindrance. And they can enhance the internal efficiency of the conjugated polymer as emissive layer in PLED because of the restraint of inter-chain interaction by the avoidance of close packing to give decent device performance.     

Efficient white polymer-light-emitting-diodes based on polyfluorene end-capped with yellowish-green fluorescent dye and blended with a red phosphorescent iridium complex

A novel series of blue and yellowish-green light-emitting single polymers were prepared by end-capping of low contents of 4-bromo-7H-benzo [de]naphtha[2′,3′:4,5]imidazo[2,1-a]isoquinolin-7-one (M1) into polyfluorene. Electroluminescence (EL) spectra of these polymers exhibit blue emission (λ_max = 430/460 nm) from the fluorene segments and yellowish-green emission (λ_max = 510/530 nm) from the M1 units. For the polymer (PFNAP-0.06) with the M1 unit content of 0.06 mol-%, its EL spectrum shows balanced intensities of blue emission and yellowish-green emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.25, 0.34). The maximum brightness of the device prepared from the polymer (PFNAP-0.06) is 6704 cd/m² at 10 V with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) [PEDOT:PSS]/PVK/emission layer/Ca/Ag. A new white polymer-light-emitting-diode (WPLED) can be developed from the single polymer (PFNAP-0.06) system blended with a red phosphorescent iridium complex [Bis(2-[2′-benzothienyl)-pyridinato-N,C^3′] iridium (acetylacetonate) (BtpIr)]. We were able to obtain a white-light-emission device by adjusting the molar ratio of BtpIr to PFNAP-0.06 with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) [PEDOT:PSS]/PVK/emission layer/Ca/Ag. The brightness in such a device configuration is 4030 cd/m² at 9 V with CIE coordinates of (0.32, 0.34).     

Metallo-homopolymer and metallo-copolymers containing light-emitting poly(fluorene/ethynylene/(terpyridyl)zinc(II)) backbones and 1,3,4-oxadiazole (OXD) pendants

A series of novel metallo-polymers containing light-emitting poly(fluorene/ethynylene/(terpyridyl)zinc(II)) backbones and electron-transporting 1,3,4-oxadiazole (OXD) pendants (attached to the C-9 position of fluorene by long alkyl spacers) were synthesized by self-assembled reactions. The integrated ratios of ¹H NMR spectra reveal a facile result to distinguish the well-defined main-chain metallo-polymeric structures which were constructed by different monomer ligand systems (i.e. single, double, and triple monomer ligands with various pendants). Furthermore, UV-vis and photoluminescence (PL) spectral titration experiments were carried out to verify the metallo-polymeric structures by varying the molar ratios of zinc(II) ions to monomers. As a result, the enhancement of thermal stability (T_d) and quantum yields were introduced by the metallo-polymerization, and their physical properties were mainly affected by the nature of the pendants. The photophysical properties of these metallo-polymers exhibited blue PL emissions (around 418 nm) with quantum yields of 34-53% (in DMF). In contrast to metallo-polymers containing alkyl pendants, the quantum yields were greatly enhanced by introducing 1,3,4-OXD pendants but reduced by carbazole (CAZ) pendants. Moreover, electroluminescent (EL) devices with these light-emitting metallo-polymers as emitters showed green EL emissions (around 550 nm) with turn-on voltages of 6.0-6.5 V, maximum efficiencies of 1.05-1.35 cd A⁻¹ (at 100 mA/cm⁻²), and maximum luminances of 2313-3550 cd/m² (around 15 V), respectively.     

A water-solubilized, segmented, alternating block copolymer of a 1,4-bis-styrylbenzene with polyethylene glycol

The synthesis and characterization of a new segmented alternating copolymer is described, having monodisperse, partially methoxy-substituted bis-1,4-styrylbenzene chromophores linked with polyethylene glycol segments (average MW 1000) at the terminal aryl rings, so that the chromophore long axis lies along the polymerization vector. The product polymer is a blue-emitting material that is soluble in organic solvents and water. It is a waxy solid with a degree of polymerization of ∼3-6, a melting transition at 35 °C and good thermogravimetric stability up to 300 °C. It exhibits blue photoluminescence (PL) at 437 nm in chloroform, and at 445-465 nm in water, with relative PL quantum yields of 0.7 and 0.3, respectively. Its neat film luminescence maximum is 460 nm; solid state blending with PMMA blue shifts the emission to 440 nm at 10% polymer in PMMA.     

New soluble unsaturated polyketone derived from diarylidenecycloalketone: synthesis and optical and electrochemical properties of π-conjugated poly(diarylidenecyclohexanone) with long side chains

A new type of unsaturated polyketone having cyclohexanone moiety in a π-conjugated main chain was prepared by polycondensation between 2,6-bis(4-bromobenzylidene)cyclohexanone and 2,5-dihexyloxy-p-phenylene diboric ester in the presence of Pd(PPh₃)₄. The polymer had good solubility in common organic solvents. Analysis by gel permeation chromatography (GPC; polystyrene standards) showed that the polymer had M_n and M_w values of 7800 and 18?200, respectively. The polymer exhibited a [η] value of 0.70 dl g⁻¹ in benzene at 30 °C. The chloroform solution of the polymer showed an UV-Vis peak at 392 nm, and the PL spectrum gave a peak at 533 nm. DSC exhibited that the polymer had a T_g of 85 °C. The DSC data, observation with a polarizing microscope, X-ray diffraction data and UV-Vis data of the obtained polymer showed a phase transition above 200 °C. TGA showed that the polymer had good thermal stability with 5 wt% loss temperature of 407 °C under N₂. Electrochemical oxidation (or p-doping) of the polymer started at about 0.7 V vs. Ag/AgNO₃ and gave a peak at 1.06 V vs. Ag/AgNO₃ with a color change of the film from yellow to deep red. The color change was followed by UV-Vis spectroscopy. The corresponding p-dedoping peak appeared at 0.58 V vs. Ag/AgNO₃.     

Largely enhanced LED efficiency of carbazole-fluorene-silole copolymers by using TPBI hole blocking layer

A new series of soluble 3,6-carbazole-fluorene-silole copolymers (PCz-F-S) with M_w up to 52.1 kDa were synthesized by Suzuki coupling reactions. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence (PL), and electroluminescence (EL) spectra. The main absorption peaks of solutions and films of the copolymers are at 354 nm and 347 nm, respectively, showing the combined contribution from the 3,6-carbazole and fluorene blocks. The silole absorption is at wavelength range between 400 nm and 500 nm. Compared with the solution absorption, largely decreased relative absorption of the silole to the 3,6-carbazole and fluorene blocks can be found for the films of the copolymers. The copolymers possess HOMO levels of around −5.36 eV, mainly from the contribution of 3,6-carbazole. Under excitation, the films of the copolymers show silole-dominated green emissions because of PL excitation energy transfer, with high absolute PL quantum yields up to 86%. EL devices with a configuration of ITO/PEDOT/PCz-F-S/Ba/Al only display a maximum external quantum efficiency of 0.48% whereas a device configuration of ITO/PEDOT/PCz-F-S/TPBI/Ba/Al with TPBI hole blocking layer greatly boosts the efficiency to 3.03% for a practical brightness of 236 cd/m². The improved EL efficiency suggests that more balanced charge injection and transport can be realized by inserting the TPBI hole blocking layer.     

Synthesis, thermal stability, light emission, and fluorescent photopatterning of poly(diphenylacetylene)s carrying naphthalene pendant groups

Naphthalene (Nap)-containing poly(diphenylacetylene)s with different spacer lengths (-{C₆H₅CC[C₆H₄O(CH₂)_mO-Nap]}_n-; P1(m), m = 4, 6, 8) are synthesized. The monomers are prepared by etherifications of 1,m-dibromoalkanes with 1-naphthol and 1-(4-hydroxy)phenyl-2-phenylacetylene and are polymerized by TaCl₅-n-Bu₄Sn and WCl₆-Ph₄Sn catalysts. Whereas the tantalum-based catalyst gives insoluble products in low yields, the tungsten-based catalyst furnishes soluble polymers with high molecular weights (M_w up to 5.0 × 10⁴) in satisfactory yields (up to 62%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, UV, PL, and EL analyses. All the polymers are thermally stable: while the polymers lose 5% of their weights at ∼420 °C under nitrogen, no decreases in molecular weights are found after they have been annealed at 200 °C for 2 h in air. When their THF solutions are photoexcited, the polymers emit strong green lights with high efficiencies (up to 98%). No significant shifts in the photoluminescence spectra are observed when the polymers are cast into thin solid films, suggestive of little involvement of aggregative or excimeric emission. A multilayer EL device with a configuration of ITO/P1(8):PVK/BCP/Alq₃/LiF/Al is constructed, which emits a green light of 520 nm with a maximum external quantum efficiency of 0.16%. The spectral stability is outstanding: no recognizable change is observed in the EL spectrum when the device current is raised. Irradiation of a film of P1(8) through a mask photooxidizes and quenches the emission of the exposed regions, resulting in the formation of two-dimensional luminescent photopatterns.     

Electrospray deposition of polymer thin films for organic light-emitting diodes

Electrospray process was developed for organic layer deposition onto polymer organic light-emitting diode [PLED] devices in this work. An electrospray can be used to produce nanometer-scale thin films by electric repulsion of microscale fine droplets. PLED devices made by an electrospray process were compared with spin-coated ones. The PLED device fabricated by the electrospray process showed maximum current efficiency of 24 cd/A, which was comparable with that of the spin-coating process. The electrospray process required a higher concentration of hole and electron transport materials in the inks than spin-coating processes to achieve PLED maximum performance. Photoluminescence [PL] at 407 nm was observed using electrosprayed poly(N-vinyl carbazole) films, whereas a peak at 410 nm was observed with the spin-coated ones. Similar difference in peak position was observed between aromatic and nonaromatic solvents in the spin-coating process. PLED devices made by the electrospray process showed lower current density than that of spin-coated ones. The PL peak shift and reduced current of electrosprayed films can therefore be attributed to the conformation of the polymer.     

Synthesis and characterization of alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units

A series of soluble alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units are synthesized by palladium-catalyzed Suzuki coupling reaction. All polymers demonstrate green colors of photoluminescence (PL) in chloroform, good thermal stability (with decomposition temperatures above 436 °C), and high glass transition temperatures (in the range of 120-144 °C). Owing to the large steric hindrance of diaryl substituents on bithiophenes in the polymers (P2-P4), the aggregation of solids is reduced as well as the solubility is improved, so the performance of their PLED devices are superior to that of the non-substituted polymer (P1). Compared with P1, the introduction of substitutents at 3,3′-position of bithiophene in P2-P4 has significant effects on the photophysical properties of resulting polymers in solution and solid states. Though the PL quantum yield of P1 is much higher than those of diaryl-substituted polymers (P2-P4), the PLED device of P1 has the worst electroluminescence (EL) properties due to the poor solubility of P1. Consequently, among these polymers, the device made of P3 as an emitter has the highest luminance of 2590 cd/m² at 9.5 V. For optimum device performance, a device of P3 blended with PVK can be further enhanced to a brighter luminance of 4284 cd/m² at 18 V.     

Synthesis of a soluble conjugated copolymer based on dialkyl-substituted dithienothiophene and its application in photovoltaic cells

A soluble conjugated alternating 3,5-didecanyldithieno[3,2-b:2′,3′-d]thiophene-thiophene copolymer was synthesized by palladium(0)-catalyzed Stille coupling reaction. The thermal, absorption, emission, electrochemical, and photovoltaic properties of the polymer were examined. A weight-average molecular weight around 6.2 × 10⁴ and a polydispersity index of 1.8 was estimated for the polymer using gel permeation chromatography. The polymer exhibits good thermal stability with decomposition temperature of 340 °C and glass-transition temperature of 136 °C. The polymer shows strong absorption peaked at 505 nm in diluted solution and 518 nm in thin film with an optical band gap 2.0 eV. The polymer exhibits intense emission located at 550 nm in solution and 603 nm in film. The HOMO and LUMO energies of the polymer were estimated to be −5.4 and −3.4 eV, respectively, by cyclic voltammetry. Polymer solar cells were fabricated based on the blend of the polymer and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The power conversion efficiency of 0.7% was achieved under AM 1.5, 100 mW/cm² using polymer:PCBM (1:4, w/w) as active layer.     

Synthesis and characterization of the soluble luminescent poly[2-decyloxy-5-(4’-ethoxyphenyl)-1,4-phenylenevinylene]

Summary A new soluble luminescent poly[2-decyloxy-5-(4^′-ethoxyphenyl)-1,4-phenylene-vinylene] (DEP-PPV) is prepared by the dehydrohalogenation of 1,4-bis(bromo-methyl)-2-decyloxy-5-(4^′-ethoxyphenyl) benzene in this study. The structure and properties of the DEP-PPV are examined by ¹H NMR, FT-IR, UV/VIS, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The incorporation of a decyloxy substituent in the 2-position of phenylene ring makes the DEP-PPV soluble in organic solvents and eliminates tolan-bis-benzyl structure defects. The energy band gap of DEP-PPV in tetrahydrofuran is 2.36 eV. The PL peak of DEP-PPV solution shifts to higher wavelength as the solution concentration increases. The PL spectrum of the DEP-PPV film shows a peak at 546 nm and the one of the pristine PPV film does at 540 nm. This red shift of PL peak for the DEP-PPV as compared with that for the PPV indicates that the incorporation of a conjugated ethoxyphenyl group on the phenylene ring can increase the conjugation length of phenylenevinylene units in the DEP-PPV. With the DEP-PPV acting as a light-emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DEP-PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 530 nm, which corresponds to the yellowish-green light. The turn-on voltage of the device is about 16 V. Its maximum brightness is 46 cd/m² at a voltage of 18 V.     

Electrophosphorescence from iridium complex-doped mesogen-jacketed polymers

A mesogen-jacketed polymer P-Ct {poly{2,5-bis[(5-tert-butylphenyl)-1,3,4-oxadiazole]styrene}} has been investigated as a host material for IrMDPP [Ir(III)bis(5-methyl-2,3-diphenylpyrazine) (acetyl acetonate)] doped polymer electrophosphorescent device. It was found that the device with P-Ct was more efficient than that with PVK. The maximum luminance and external luminous efficiency can reach 3702 cd/m² and 0.83 cd/A, respectively, which were higher than those of device with PVK (1999 cd/m² and 0.68 cd/A), which can be partly explained by the more balanced carrier injection and transportation and longer lifetime of excitons in P-Ct-TPD-IrMDPP. It was also found that as the IrMDPP content increased in P-Ct-TPD, the EL spectra color shifts from green-yellow to yellow-orange and were different from PL spectra, which was partly due to the dominating role of direct charge-trapping and recombination in the EL process over the energy-transfer routes.     

Defect-free Poly(9,9-bis(2-ethylhexyl)fluorene-2,7-vinylene) for Polymer Light-Emitting Diode (PLED) Devices

The π-conjugated light-emitting polymer poly(9,9-bis(2-ethylhexyl)fluorene-2,7-vinylene) (PEHFV), was synthesized in defect-free form via Horner-Emmons coupling. The structure and properties of the polymer were characterized by ¹H NMR, ¹³C NMR, UV-vis, photoluminescence (PL), and electroluminescence (EL) spectroscopies as well as gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The weight-average molecular weight (M_w) and polydispersity of the PEHFV were 34,000 g/mol and 2.3, respectively. The UV-vis spectra showed absorption maxima at 425 and 452 nm, and the PL emission spectra showed a maximum at 505 nm with a shoulder at 541 nm. The polymer was soluble in common organic solvents and easily spin-coated on indium-tin oxide (ITO)-coated glass substrates. A double-layer light-emitting device with an ITO/PEDOT:PSS/PFV/Al configuration was fabricated. The turn-on voltage for the PEHFV device was observed at 3.0 V.