Synthesis of new polyfluorene copolymers with a comonomer containing triphenylamine units and their applications in white‐light‐emitting diodes

Novel conjugated polyfluorene copolymers, poly[9,9‐dihexylfluorene‐2,7‐diyl‐co‐(2,5‐bis(4′‐diphenylaminostyryl)‐phenylene‐1,4‐diyl)]s (PGs), have been synthesized by nickel(0)‐mediated polymerization from 2,7‐dibromo‐9,9‐dihexylfluorene and 1,4′‐dibromo‐2,5‐bis(4‐diphenylaminostyryl)benzene with various molar ratios of the monomers. Because of the incorporation of triphenylamine (TPA) moieties, PGs exhibit much higher HOMO levels than the corresponding polyfluorene homopolymers and are able to facilitate hole injection into the polymer layer from the anode electrode in light‐emitting diodes. Conventional polymeric light‐emitting devices with the configuration ITO/PEDOT:PSS/polymer/Ca/Al have been fabricated. A light‐emitting device produced with one of the PG copolymers (PG10) as the emitting layer exhibited a voltage‐independent and stable bluish‐green emission with color coordinates of (0.22, 0.42) at 5 V. The maximum brightness and current efficiency of the PG10 device were 3370 cd/m² (at 9.6 V) and 0.6 cd/A, respectively. To realize a white polymeric light‐emitting diode, PG10 as the host material was blended with 1.0 wt % of a red‐light‐emitting polymer, poly[9,9‐dioctylfluorene‐2,7‐diyl‐alt‐2,5‐bis(2‐thienyl‐2‐cyanovinyl)‐1‐(2′‐ethylhexyloxy)‐4‐methoxybenzene‐5′,5′‐diyl] (PFR4‐S), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV). The device based on PG10:PFR4‐S showed an almost perfect pure white electroluminescence emission, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.36) at 8 V; for the PG10:MEH‐PPV device, the CIE coordinates at this voltage were (0.30, 0.40) with a maximum brightness of 1930 cd/m². Moreover, the white‐light emission from the PG10:PFR4‐S device was stable even at different driving voltages and had CIE coordinates of (0.34, 0.36) at 6 V and (0.31, 0.35) at 10 V. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1199–1209, 2007     

Synthesis and characterization of hyperbranched polyfluorenes containing triarylpyrazoline cores towards efficient blue light‐emitting diodes

New series of hyperbranched polyfluorenes containing triarylpyrazoline cores, PFZ10 , PFZ20 , PFNZ10 , and PFNZ20 , have been synthesized according to the “A₂ + A′₂ + B₃” Suzuki coupling method. The structures and property of the monomers and conjugated polymers were characterized by elemental analysis, gel permeation chromatography, cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry, and UV–visible absorption, ¹H NMR, ¹³C NMR, and photoluminescence spectroscopies. All these polymers exhibited good solubility in common organic solvents and good thermal stability. The long‐wavelength emission of polyfluorenes had been effectively reduced in these hyperbranched polymers. Standard polymer light emitting devices (PLEDs) from PFZ10 , PFZ20 , PFNZ10 , and PFNZ20 , with the configuration of ITO/PEDOT/polymer/TPBI/Alq₃/Mg:Ag, exhibited good electroluminescence (EL) properties The PLED based on PFNZ10 emitted pure blue light with a low turn‐on voltage of 5.3 V and a high EL efficiency of about 1.93%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5296–5307, 2007     

Synthesis and electroluminescence properties of white‐light single polyfluorenes with high‐molecular weight by click reaction

We reported a new way to synthesize single‐chain white light‐emitting polyfluorene (WPF) with an increased molecular weight using azide‐alkyne click reaction. Four basic polymers with specific end‐capping, which exhibited high‐glass transition temperatures (T_g > 100 °C) and excellent thermal stability, were used as foundations of the WPF's synthesis; a blue‐light polymer (PFB2) end‐capped with azide groups can easily react with acetylene end‐capped polymers (PFB1, PFG1, and PFR1, which are emitting blue‐, green‐ and red‐light, respectively) to form triazole‐ring linkages in polar solvents such as N,N‐dimethylforamide/toluene co‐solvent at moderate temperature of 100 °C, even without metal‐catalyst. Several WPFs that consist of these four basic polymers in certain ratios were derived, and the polymer light‐emitting diode device based on the high‐molecular weight WPF was achieved and demonstrated a maximum brightness of 7551 cd/m² (at 12.5 V) and a maximum yield of 5.5 cd/A with Commission Internationale de l'Eclairage coordinates of (0.30, 0.33) using fine‐tuned WPF5 as emitting material. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Copolyfluorenes containing phenothiazine or thiophene derivatives: Synthesis,characterization, and application in white‐light‐emitting diodes

Four copolyfluorenes chemically doped with 0.1 and 1 mol % 3,7‐bis[2‐thiophene‐2‐yl)‐2‐cyanovinyl]phenothiazine ( PFPhT ) or 2,5‐bis[2‐(thiophene‐2‐yl)‐2‐cyanovinyl]thiophene chromophores ( PFThT ) were synthesized using the Suzuki coupling reaction and applied in white‐light‐emitting devices. They were characterized by GPC, elemental analysis, DSC, TGA, optical spectra, and cyclic voltammetry. They exhibited good thermal stability (T_d > 420 °C) and moderate glass transition temperatures (>95 °C). The PhT‐Br and ThT‐Br showed PL peaks at 586 and 522 nm (with a shoulder at 550 nm). In film state, PL spectra of the copolymers comprised emissions from the fluorene segments and the chromophores due to incomplete energy transfer. Both monomers exhibited low LUMO levels around ?3.50 to ?3.59 eV, whereas the PhT‐Br owned the higher HOMO level (?5.16 eV) due to its electron‐donating phenothiazine core. Light‐emitting diodes with a structure of ITO/PEDOT:PSS/copolymer/Ca(50 nm)/Al(100 nm) showed broad emission depending on the chromophore contents. The maximum brightness and maximum current efficiency of PFPhT2 ( PFThT1 ) device were 8690 cd/m² and 1.43 cd/A (7060 cd/m² and 0.98 cd/A), respectively. White‐light emission was realized by further blending PFPhT2 with poly(9,9‐dihexylfluorene) (w/w = 10/1), with the maximum brightness and maximum current efficiency being 10,600 cd/m² and 1.85 cd/A. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 833–844, 2009     

Synthesis and characterization of new light‐emitting copolymers in polymeric‐light‐emitting‐diode device fabrications

A series of thiophene‐containing photoactive copolymers consisting of alternating conjugated and nonconjugated segments were synthesized. The ¹H NMR spectra corroborated the well‐defined structures, and the copolymers not only were soluble in common organic solvents but also had high glass‐transition temperatures (ca. 130 °C) and good thermal stability up to 390 °C. Introducing aliphatic functional groups, such as alkyl or alkoxyl, into chromophores of the copolymers redshifted the photoluminescence spectra and lowered the optical bandgaps. The electrochemical bandgaps calculated from cyclic voltammetry agreed with the optical bandgaps and thus indicated that electroluminescence and photoluminescence originated from the same excited state. The energy levels (highest occupied molecular orbital and lowest unoccupied molecular orbital) of all the copolymers were lower than those of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1.4‐phenylenevinylene] MEH–PPV, indicating balanced hole and electron injection, which led to improved performance in both single‐layer and double‐layer polymeric‐light‐emitting‐diode devices fabricated with these copolymers. All the copolymers emitted bluish‐green or green light above the threshold bias of 5.0 V under ambient conditions. At the maximum bias of 10 V, the electroluminescence of a device made of poly(2‐{4‐[2‐(3‐ethoxy phenyl)ethylene]phenyl}‐5‐{4‐[2‐(3‐ethoxy,4‐1,8‐octanedioxy phenyl)ethylene]phenyl}thiophene) was 5836 cd/m². The external electroluminescence efficiency decreased with the lifetime as the polymer degraded. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3954–3966, 2004     

Improving optoelectronic properties of the 2,7‐polyfluorene derivatives with carbazole and oxadiazole pendants by incorporating the blue‐emitting iridium complex pendants in C‐9 position of fluorine unit

To study the influence of a blue‐emitting iridium complex pendant on the optoelectronic properties of its 2,7‐polyfluorene (PF) derivatives with the carbazole and oxadiazole pendants, a class of 2,7‐PF derivatives containing carbazole, oxadiazole, and/without the cyclometalated iridium complex pendants in the C‐9 positions of fluorene unit were synthesized. Their thermal, photophysical, electrochemical, and electroluminescent (EL) properties were investigated. Among these 2,7‐PF derivatives (P 1 –P 4 ), P 2 and P 3 exhibited higher photoluminescence efficiency in dichloromethane and better EL properties in the single‐emissive‐layer polymer light‐emitting devices. The highest brightness of 3888 cd/m² and the maximum current efficiency of 2.9 cd/A were obtained in the P 2 ‐ and P 3 ‐based devices, respectively. The maximum brightness and efficiency levels were 1.7 and 2.1 times, respectively, higher than the corresponding levels from the parent 2,7‐PF derivative (P 1 )‐based devices. Our work indicated that EL properties of 2,7‐PF derivatives can be improved by introducing the blue‐emitting iridium complex into the alkyl side chain of fluorine unit as pendant. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular design of efficient white‐light‐emitting fluorene‐based copolymers by mixing singlet and triplet emission

A new strategy to realize efficient white‐light emission from a binary fluorene‐based copolymer (PF‐Phq) with the fluorene segment as a blue emitter and the iridium complex, 9‐iridium(III)bis(2‐(2‐phenyl‐quinoline‐N,C³′)(11,13‐tetradecanedionate))‐3,6‐carbazole (Phq), as a red emitter has been proposed and demonstrated. The photo‐ and electroluminescence properties of the PF‐Phq copolymers were investigated. White‐light emission with two bands of blue and red was achieved from the binary copolymers. The efficiency increased with increasing concentration of iridium complex, which resulted from its efficient phosphorescence emission and the weak phosphorescent quenching due to its lower triplet energy level than that of polyfluorene. In comparison with the binary copolymer, the efficiency and color purity of the ternary copolymers (PF‐Phq‐BT) were improved by introducing fluorescent green benzothiadiazole (BT) unit into polyfluorene backbone. This was ascribed to the exciton confinement of the benzothiadiazole unit, which allowed efficient singlet energy transfer from fluorene segment to BT unit and avoided the triplet quenching resulted from the higher triplet energy levels of phosphorescent green emitters than that of polyfluorene. The phosphorescence quenching is a key factor in the design of white light‐emitting polyfluorene with triplet emitter. It is shown that using singlet green and triplet red emitters is an efficient approach to reduce and even avoid the phosphorescence quenching in the fluorene‐based copolymers. The strategy to incorporate singlet green emitter to polyfluorene backbone and to attach triplet red species to the side chain is promising for white polymer light‐emitting diodes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 453–463, 2008     

Synthesis and characterization of highly stable blue‐light‐emitting hyperbranched conjugated polymers

Polyfluorene homopolymer ( P1 ) and its carbazole derivatives ( P2 – P4 ) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, ¹H NMR, ¹³C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer ( P1 ). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008     

Pure white‐light‐emitting diodes from phosphorescent single polymer systems

New white polymeric light‐emitting diodes from phosphorescent single polymer systems have been developed using a blue‐light‐emitting fluorene monomer copolymerized with a red‐light‐emitting phosphorescent dye, and end‐capped with a green‐light‐emission dye. All of the copolymers have good thermal stability with 5% weight loss temperatures at 380–413 °C and glass transition temperatures at 75–137 °C. We obtained white‐light‐emission devices by adjusting the molar ratio of the comonomers with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid)/polyvinylcarbazole (PVK)/emission layer/Ca/Ag. The highest brightness in such a device configuration is 300 cd/m² at a current density of 2900 A/m² with high white color quality (Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.34)). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 464–472, 2008     

High‐efficiency doped polymeric organic light‐emitting diodes

Fabrication of polymer light‐emitting diodes based on emission from the phosphorescent molecule fac‐tris(2‐phenylpyridine) iridium doped into a poly(N‐vinyl carbazole) host are reported. For single‐layered devices with magnesium‐silver cathodes, the luminance efficiency at 20 mA/cm² was measured as 8.7 cd/A. This efficiency could be increased by over a factor of two by incorporation of evaporated small‐molecule layers into the device structure. Significant increases in device efficiency were also obtained without these evaporated layers by modification of the electrodes. Incorporation of 3,4‐poly(ethylene dioxythiophene):poly(styrene sulfonate) at the anode improved the device efficiency but had little impact on drive voltage. Insertion of lithium fluoride at the cathode resulted in no improvement in performance for magnesium‐silver and aluminum cathodes, but a significant improvement was realized in efficiency and drive voltage for calcium‐aluminum cathodes. Excellent device performance was observed for all three cathode metals used in conjunction with cesium fluoride. Through optimization of the electrodes and emitter‐layer thickness, devices exhibiting efficiencies as high as 37.3 cd/A are realized. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2715–2725, 2003     

Synthesis and characterization of indeno[1,2‐b]fluorene‐based white light‐emitting copolymer

An indenofluorene‐based copolymer containing blue‐, green‐, and red light‐emitting moieties was synthesized by Suzuki polymerization and examined for application in white organic light‐emitting diodes (WOLEDs). Tetraoctylindenofluorene (IF), 2,1,3‐benzothiadiazole (BT), and 4,7‐bis(2‐thienyl)‐2,1,3‐benzothiadiazole (DBT) derivatives were used as the blue‐, green‐, and red‐light emitting structures, respectively. The number‐average molecular weight of the polymer was determined to be 25,900 g/mol with a polydispersity index of 2.02. The polymer was thermally stable (T_d = ～398 °C) and quite soluble in common organic solvents, forming an optical‐quality film by spin casting. The EL characteristics were fine‐tuned from the single copolymer through incomplete fluorescence energy transfer by adjusting the composition of the red/green/blue units in the copolymer. The EL device using the indenofluorene‐based copolymer containing 0.01 mol % BT and 0.02 mol % DBT units ( PIF‐BT01‐DBT02 ) showed a maximum brightness of 4088 cd/m² at 8 V and a maximum current efficiency of 0.36 cd/A with Commission Internationale de L'Eclairage (CIE) coordinates of (0.34, 0.32). The EL emission of PIF‐BT01‐DBT02 was stable with respect to changes in voltage. The color emitted was dependent on the thickness of the active polymer layer; layer (～60 nm) too thin was unsuitable for realizing WOLED via energy transfer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3467–3479, 2009     

Synthesis of copolyfluorenes containing green chromophores based on triphenylamine unit and their application in light‐emitting diodes

Two series of new copolyfluorenes ( PFTP, PFTT ) were prepared by the Suzuki coupling reaction from two green‐emitting dibromo monomers (TP‐Br, TT‐Br) based on triphenylamine unit to be applied in white light electroluminescent devices. They were characterized by molecular weight determination, elemental analysis, DSC, TGA, absorption and photoluminescence spectra, and cyclic voltammetry. The estimated actual contents of the TP and TT chromophores were lower than 7.8 mol % and 1.9 mol % for PFTP and PFTT , respectively. In film state both copolyfluorenes showed photoluminescence at 400–470 and 470–600 nm originated from fluorene segments and the chromophores, respectively, due to incomplete energy transfer. Light‐emitting diodes with a structure of ITO/PEDOT:PSS/copolymer/Ca(50 nm)/Al(100 nm) showed major emission at 493–525 nm, plus minor emission at 400–470 nm when chromophore contents were low. The maximum brightness and maximum current efficiency of PFTP2 device were 8370 cd/m² and 1.47 cd/A, whereas those of PFTT1 device were 9440 cd/m² and 1.77 cd/A, respectively. Tri‐wavelength white‐light emission was realized through blending PFTT1 with poly(9,9‐dihexylfluorene) and a red‐emitting iridium complex, in which the maximum brightness and CIE coordinates were 6880 cd/m² and (0.31, 0.33), respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1553–1566, 2009     

Synthesis and optoelectronic properties of silole‐containing polyfluorenes with binary structures

2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high M_w up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007     

Synthesis and electro‐optical properties of light‐emitting polymers containing oxadiazole derivatives for light‐emitting diodes applications

Two PPV‐based bipolar polymers containing 1,3,4‐oxadiazole pendant groups were synthesized via the Gilch polymerization reaction for use in light‐emitting diodes (LEDs). The resulting polymers were characterized using ¹H and ¹³C NMR, elemental analysis, DSC, and TGA. These polymers were found to be soluble in common organic solvents and are easily spin‐coated onto glass substrates, producing high optical quality thin films without defects. The electro‐optical properties of ITO/PEDOT/polymer/Al devices based on these polymers were investigated using UV‐visible, PL, and EL spectroscopy. The turn‐on voltages of the OC₁Oxa‐PPV and OC₁₀Oxa‐PPV devices were found to be 8.0 V. The maximum brightness and luminescence efficiency of the OC₁Oxa‐PPV device were found to be 544 cd/m² at 19 V and 0.15 cd/A, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1098–1110, 2008     

Conjugated and partially conjugated 2,5‐diphenylthiophene‐containing light‐emitting copolymers in polymeric light‐emitting diode (PLED) device fabrications

To study the effect of nonconjugation on polymeric and photophysical properties of thiophene‐containing polymers, new light‐emitting copolymers comprising either alternate 2,5‐diphenylthiophene and vinylene or alternate 2,5‐diphenylthiophene and aliphatic ether segments were synthesized. Both copolymers contained 2,5‐diphenylthiophene as the major chromophore and emitted a sky bluish fluorescence in dilute solution (10^?2 mg/mL). With a rigid and planarity structure and the concomitant crystallinity, the former copolymer (fully conjugated) possessed a higher quantum efficiency, a higher glass‐transition temperature, and a better thermal stability. In contrast, the latter copolymer (conjugated–nonconjugated) had better solubility and provided enhanced photophysical properties for the fabricated polymeric light‐emitting diode (PLED) device: at 15 V, the maximum current and brightness were 110 mA/cm² and 4289 cd/m², respectively, and the electroluminescence efficiency remained constant at approximately 4.9 cd/A in a voltage range of 8 to 14 V. The existence of intramolecular/intermolecular aggregates in the latter copolymer was corroborated from the the UV–vis and photoluminescence spectra of its solutions. With an increase in solution concentration, the shape and λ_max of the photoluminescence spectrum were redshifted. In a solution with a concentration as high as 10 mg/mL, the redshift was so drastic that the photoluminescence spectrum was nearly identical to that of a solid‐film. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6061–6070, 2004     

Synthesis and characterization of polyfluorenes containing bisphenazine units

Novel conjugated copolymers based on 9,9‐dioctylfluorene and bisphenazine (BP) were synthesized by Suzuki polymerization. Energy transfer from the conjugated main chain to the BP moieties was observed. Full energy transfer was achieved when the molar content of the bisphenazine was 20% (20BPPF) in toluene solution. The similar phenomena were observed even for 1% bisphenazine content copolymer (1BPPF) in film. The lowest occupied molecular orbital (LUMO) energy levels (?3.06 eV) of the copolymers were lower than that of the polyfluorene homopolymer (PFO; ?2.65 eV), indicating that the introduction of the BP unit was benefit to electron injection. Single‐layer electroluminescent devices (ITO/PEDOT:PSS/polymer/LiF/Al) were fabricated to investigate their electroluminescence (EL) performances. The maximum brightness and current efficiency of all BPPF copolymers surpassed the PFO homopolymer. The best single‐layer device was based on 5BPPF, with a maximum brightness of 1532 cd/m² and current efficiency of 1.09 cd/A. Much higher efficiency could be achieved for multilayer EL devices of 5BPPF (ITO/PEDOT:PSS/PVK/polymer/TPBI/LiF/Al), which showed a maximum current efficiency of 10.01 cd/A. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1990–1999, 2010     

Phosphorescent organic light‐emitting diodes using an iridium complex polymer as the solution‐processible host material

We prepared an iridium polymer complex having 2‐phenylpyridine as a η²‐cyclometallated ligand, a new OLED containing a solution‐processible iridium polymer as a host, and a phosphorescent iridium complex, [Ir(piq‐^tBu)₃] as a guest. This is the first example to apply a phosphorescent iridium complex polymer to a host material in a phosphorescent OLED. A phosphine copolymer ligand made from methyl methacrylate (MMA) and 4‐styryldiphenylphosphine can be used as an anchor polymer, which coordinates to luminescent iridium units to form a host metallopolymer easily. The OLED containing the host iridium‐complex polymer film, in which the guest, 2 wt % Ir(piq‐^tBu)₃, was doped, showed red electroluminescence as a result of efficient energy transfer from the iridium polymer host to the iridium guest. The maximum current efficiency of the device was 1.00, suggesting that a soluble iridium complex polymer can be used as a solution‐processible polymer host in EL devices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4358–4365, 2009     

Synthesis and characterization of fluorene‐based copolymers containing benzothiadiazole derivative for light‐emitting diodes applications

Five new thermally robust electroluminescent fluorene‐based conjugated copolymers, including poly[2,7‐(9,9‐dioctylfluorene)‐co‐4,7‐{5,6‐bis(3,7‐dimethyloctyloxymethyl)‐2,1,3‐(benzothiadiazole)}] ( PFO‐P2C₁₀BT ) were synthesized and used to fabricate the efficient polymer light‐emitting diodes (PLEDs). The glass transition temperatures of the polymers were found to be higher than that of poly(9,9‐dialkylfluorenes) and are in the range 113–165 °C. We fabricated PLEDs in indium‐tin oxide/PEDOT/light‐emitting polymer/cathode configurations using either double‐layer LiF/Al or triple‐layer Alq₃/LiF/Al cathode structures. The new copolymers were found to have emission colors that vary from greenish blue (491 nm) to green (543 nm) depending on the copolymer composition. The maximum brightness and luminance efficiency of these PLEDs were found to be up to 5347 cd/m² and 1.51 cd/A at 10 V, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6762–6769, 2008     

Polyfluorenes minimally doped with 1,4‐bis(2‐thienyl‐2‐cyanovinyl)benzene chromophore: Their synthesis,characterization, and application to white‐light‐emitting materials

Copolyfluorenes ( PFR1 and PFR2 ), chemically doped with 0.1 and 0.025 mol % 2,5‐dihexyloxy‐1,4‐bis(2‐thienyl‐2‐cyanovinyl)benzene (MR chromophere) were synthesized by the Suzuki coupling reaction. The PFR s were used to fabricate white‐light‐emitting devices through incomplete energy transfer. Because of the low content of the MR chromophore, the optical, thermal, and electrochemical properties of the PFR s were almost identical to those of polyfluorene, except for their photoluminescent (PL) and electroluminescent (EL) properties. The copolymer films showed PL peaks at about 428 and 570 nm originating from fluorene segments and MR chromophores, respectively. Compared with the model compound ( MR ), the polymer chains extended the conjugation length of the MR chromophores and exhibited a 20–48 nm red‐shift in the emission band. In addition, the lower LUMO level of the MR (?3.27 eV) was expected to improve the electron injection. The EL devices [ITO/PEDOT:PSS/ PFR s/Ca (50 nm)/Al (100 nm)] showed a broad emission band, covering the entire visible region, with chromaticity coordinates of (0.36, 0.35) and (0.32, 0.30) for PFR1 and PFR2 devices, respectively. The emission color of the PFR2 device was very similar to that of a pure white light (0.33, 0.33); and the maximal brightness and current efficiency were 3011 cd/m² and 1.98 cd/A, respectively, which surpass those found for polyfluorene devices (1005 cd/m², 0.28 cd/A). A). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3703–3713, 2008     

Synthesis,characterization, and optoelectronic properties of hyperbranched polyfluorenes containing pendant benzylether dendrons

Linear polyfluorenes with low generation of side benzylether dendrons ( PLG0 , PLG1 ) and hyperbranched polyfluorenes with 1,3,5‐benzene branch unit ( PHG0 and PHG1 ) were prepared by the Suzuki coupling reaction to investigate the structural effect on optoelectronic properties. Their optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. The excimer emission of polyfluorene at about 530 nm, induced by thermal annealing, was completely suppressed by the hyperbranched structure, but the suppression was not obvious by the side benzylether dendrons. The optoelectronic performance of the EL devices (ITO/PEDOT:PSS/polymer/Ca/Al) was strongly dependent upon chemical structures of the emitting polyfluorenes. The hyperbranched PHG0 with zero generation of benzylether side groups revealed the best device performance, with maximal luminance and maximal luminance efficiency of 2350 cd/m² and 0.33 cd/A, respectively. The results suggest that incorporation of branch units with low generation of benzylether dendrons is an effective way to improve annealing stability and EL performance of the polyfluorenes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5945–5958, 2008