Polyfluorenes containing tetraphenylthiophene segments: Synthesis,photophysics, and electroluminescence

2,5‐Bis(4‐bromophenyl)‐3,4‐diphenylthiophene was synthesized from benzyl chloride and sulfur and through the subsequent bromination of the intermediate 2,3,4,5‐tetraphenylthiophene. It was condensed with 2,7‐dibromo‐9,9‐dihexylfluorene via a nickel‐mediated Yamamoto coupling reaction to afford a new series of statistical copolymers with various compositions. In addition, poly(9,9‐dihexylfluorene) (PF) was synthesized under the same conditions for comparison. All the polymers were soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, and dichloromethane. Their glass‐transition temperatures increased with an increase in the tetraphenylthiophene (TPT) content in the polymers, and they were 63–149 °C. The solutions of the polymers in THF emitted intense blue light with a photoluminescence maximum at 418–440 nm and quantum yields of 0.32–0.62. Thin films of the polymers with TPT fractions lower than 20 mol % emitted blue‐green light with two well‐resolved peaks at 445 and 520 nm and an optical band gap of about 2.85 eV. A thin film of the polymer with aTPT fraction of 50 mol % emitted pure blue light with a maximum at 419 nm and an optical band gap of 3.28 eV. An enhancement of the light‐emitting‐diode brightness by a factor of ～8 with respect to that of PF was achieved in apolymer containing 5 mol % TPT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4015–4026, 2006     

New highly luminescent cationic polyelectrolytes based on poly(phenylenevinylene‐alt‐fluorenevinylene) or poly(fluorenevinylene) derivatives and their neutral precursors

Poly(phenylenevinylene‐alt‐fluorenevinylene) ( PF ) or poly(fluorenevinylene) ( F ) derivatives that carried alkyl chains with terminal tertiary amino groups were successfully synthesized via Heck coupling. They were postquaternized by reacting with bromoethane to the corresponding cationic polyelectrolytes PFQ and FQ . The neutral polymers PF and F as well as the quaternized polymer FQ were soluble in common organic solvents such as THF, chloroform, dichloromethane, and toluene. In contrast, the quaternized polymer PFQ did not dissolve in these solvents but was soluble in environmentally friendlier solvents like water and alcohols. The neutral precursors exhibited higher thermal stability and glass‐transition temperatures than the corresponding quaternized counterparts. All polymers emitted intense blue‐greenish light in solution (462–489 nm) with relatively high photoluminescence (PL) quantum yields 0.32–0.57, and as thin films (475–557 nm) with optical band gaps of 2.48–2.57 eV. The water soluble PFQ could find potential applications as chemo or biosensor. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1481–1491, 2007     

New poly(p‐phenylene vinylene) derivatives with two oxadiazole rings per repeat unit: Synthesis,photophysical properties,electroluminescence, and metal ion recognition

Two new poly(p‐phenylene vinylene) derivatives OX1‐PPV and OX2‐PPV bearing two 1,3,4‐oxadiazole rings per repeat unit and a fully conjugated backbone with solubilizing dodecyloxy side groups were synthesized and investigated. The amorphous conjugated polymers had glass‐transition temperature values of 60–75 °C and emitted intense blue or greenish‐blue light in solution with photoluminescence (PL) emission maxima at 379–492 nm and PL quantum yields of 0.41–0.52. In the solid state they emitted yellowish‐green light with PL emission maxima at 533–555 nm. Cyclic voltammetry showed that both conjugated polymers had reversible reduction and irreversible oxidation, making them n‐type materials. The electron affinity of OX2‐PPV was estimated as 2.85 eV whereas that of OX1‐PPV was 2.75 eV. Yellow electroluminescence (EL) was achieved from single‐layer light‐emitting diodes of OX2‐PPV with an EL emission maximum at 555 nm and a brightness of 70 cd/m². Polymer OX2‐PPV, which was functionalized with 2,6‐bis(1,3,4‐oxadiazole‐2‐yl)pyridine, demonstrated sensitivity to various metal ions as a fluorescence‐mode chemosensor. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2112–2123, 2004     

Synthesis and optical properties of novel blue‐light‐emitting poly(p‐phenylene vinylene) derivatives with pendant oxadiazole or cyano groups

Two novel poly(p‐phenylene vinylene) polymers, which carried side substituents with cyano groups or 1,3,4‐oxadiazole, were synthesized by Heck coupling. They consisted of alternating conjugated segments and nonconjugated aliphatic spacers. The polymers had moderate molecular weights, were amorphous, and dissolved readily in tetrahydrofuran and halogenated organic solvents. They were stable up to approximately 340 °C in N₂ and 290 °C in air, and the anaerobic char yield was around 60% at 800 °C. The polymer with cyano side groups emitted blue light in solutions and thin films with identical photoluminescence (PL) maximum at 450 nm; this supported the idea that chain interactions were hindered even in the solid state. The PL maximum of this polymer in thin films was blueshifted upon annealing at 120 °C, indicating a thermochromic effect as a result of conformational changes in the polymer backbone. The polymer containing side substituents with oxadiazole rings emitted blue light in solutions with a PL maximum at 474 nm and blue‐greenish light in thin films with a PL maximum at 511 nm. The PL quantum yields of the polymers in tetrahydrofuran were 0.13–0.24. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1768–1778, 2004     

Synthesis,photophysics, and electroluminescent performance of stable blue‐light‐emitting copoly(9,9‐diarylfluorene)s

A series of fluorene derivatives containing nonsymmetric and bulky aromatic groups at C‐9 position were synthesized and used for the preparation of blue‐light‐emitting copolyfluorenes ( P1 – P4 ) by the Suzuki coupling polycondensation. The copolymers were characterized by molecular weight determination, elemental analysis, differential scanning calorimeter, thermogravimetric analysis, absorption and emission spectroscopy, cyclic voltammetry, and differential pulse voltammetry. Their decomposition temperatures and glass transition temperatures are 423–441 °C and >120 °C, respectively. In film state, the copolyfluorenes exhibit blue photoluminescence at 425–450 nm, which remains almost unchanged after annealing at 200 °C in air for 60 min. Polymer light‐emitting diodes [ITO/PEDOT:PSS/ P1 – P4 /Ca(50 nm)/Al(100 nm)] show stable blue‐light emission under device operation with the CIE co‐ordinates being between (0.16, 0.07) and (0.17, 0.09). The light‐emitting diodes devices from P1 and P3 containing electron‐deficient oxadiazole units display enhanced performance, with the maximum brightness and maximum current efficiency being (4510 cd/m² and 2.40 cd/A) and (2930 cd/m², 1.19 cd/A), respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2821–2834, 2009     

Synthesis,optical properties,and electroluminescence of conjugated poly(p‐phenylenevinylene) derivatives containing 1,3,4‐oxadiazole and pyridine rings in the main chain

Three new poly(p‐phenylenevinylene) derivatives—PO, POD, and POP—with oxadiazole and pyridine rings along the main chain were synthesized via Heck coupling. The polymers were amorphous and dissolved readily in common organic solvents. They showed relatively low glass‐transition temperatures (up to 42 °C) and satisfactory thermal stability. Solutions of the polymers emitted blue‐greenish light with photoluminescence (PL) emission maxima around 460 nm and PL quantum yields of 0.28–0.49. Thin films of the polymers displayed PL emission maxima at 461–521 nm, and their tendency to form aggregates was significantly influenced by the chemical structure. Light‐emitting diodes with polymers PO and POP, with an indium tin oxide/poly(ethylenedioxythiophene) (PEDOT)/polymer/Ca configuration, emitted yellow and green light, respectively, and this could be attributed to excimer emission. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3212–3223, 2004     

Synthesis and characterization of a high-efficiency light-emitting alternating copolymer

A new high-efficiency light-emitting alternating copolymer of triphenylamine and pure PPV (TPA–PPV) has been designed and synthesized. The copolymer was highly soluble in common solvents. It could be spin cast onto various substrates to give highly transparent homogeneous thin films without heat treatment. The fluorescence quantum yield in benzene is almost up to 1.00. The maximum fluorescence wavelength for this alternating copolymer appeared around 470 nm. The fluorescence of TPA–PPV solution quenched by C₆₀ was examined, and the result indicated that a strong interaction exists between TPA–PPV and C₆₀ at the exited state. A primary single-layer LED based on ITO/TPA–PPV/Al has been fabricated, and the onset voltage is only 1.5 V and a bright green light was observed. The electroluminescence spectrum gives a peak at 510 nm when the operating voltage of 17 V was applied. The photoluminescence spectrum also appeared at the same wavelength as the electroluminescence, indicating that the same excited states are involved in the two processes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2587–2594, 1999     

Synthesis,photophysics, structure‐tunable photoluminescence,and electrochemical properties of soluble poly(p‐phenylenevinylene)‐based polymers with adjacent 1,3,4‐oxadiazoles in the backbone

Three new poly(p‐phenylenevinylene)‐based polymers containing two 1,3,4‐oxadiazole moieties in the main chain per repeat unit were synthesized by Heck coupling. A single, double, or triple bond was introduced between the oxadiazoles to provide a means for modifying the polymer properties. The polymers were readily soluble in common organic solvents and showed T_g values lower than 50 °C. The color of the emissive light in both the solid state and the solution could be tuned by a change in the nature of the bond between the oxadiazole rings. The polymers emitted ultraviolet‐green light in solution with a photoluminescence (PL) emission maximum at 345–483 nm and blue‐green light at 458–542 nm in thin films. The PL quantum yields in solution were 0.36–0.43. The electrochemical properties are affected by the nature of the bond between the oxadiazoles as well. In polymers with a single bond between the oxadiazoles, a lower ionization potential was observed than in polymers with a double or triple bond. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3079–3090, 2005     

Synthesis and properties of new ultraviolet–blue‐emissive fluorene‐based aromatic polyoxadiazoles with confinement moieties

Three families of fluorene–oxadiazole‐based polymers with confinement moieties have successfully been prepared by the two‐step method for polyoxadiazole synthesis. These polymers show good solubility in common organic solvents, high thermal stability, and strong violet and blue photoluminescence in solution and as films, respectively. Their low‐lying highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels originate from the electron deficiency of an oxadiazole moiety, and this suggests that they may be useful for blue‐emitting and electron‐transport/hole‐blocking layers in electroluminescent devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 674–683, 2003     

Enhancement of color purity in blue light emitting poly(fluorene)s and poly(p‐phenylene)s with 2,6‐distyrylpyridine kinked segments along the backbone

2,6‐bis(4‐Distyrylpyridine) ( 1 ) was synthesized by the condensation of 2,6‐dimethylpyridine with 4‐bromobenzaldehyde. Two new series of soluble random or alternating polyfluorenes ( PF‐Py ) and poly‐p‐phenylenes ( PP‐Py ) with various compositions were prepared by Suzuki coupling utilizing 1 as a comonomer. These polymers showed optical band gaps of 3.00–3.07 eV and photoluminescence (PL) quantum yields in solution of 0.37–0.91 for PF‐Py and 0.29–0.38 for PP‐Py . Polymers PF‐Py emitted blue light with PL maximum at 410–424 nm in solution and 406–428 nm in thin films that was red shifted with increasing distyrylpyridine content. Polymers PP‐Py behaved as blue emitters both in solution and in solid state, with PL maximum at 416–436 nm. The optical properties of these polymers could be tuned by the reversible protonation–deprotonation process of the pyridine ring. The emitted color of the polymers in solution and thin film could be changed continuously between blue and green (PL maximum up to about 520 nm) by exposing the polymers to the acid or base environment. Thin films of PF‐Py displayed excellent color stability with a small red shift of 10 nm but without additional emission band in the long wave region of the spectrum, even after being annealed at high temperature for a long time. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4486–4495, 2005     

New series of highly phenyl‐substituted polyfluorene derivatives for polymer light‐emitting diodes

A new series of highly phenyl‐substituted polyfluorene derivatives were synthesized and characterized. The resulting polymers were amorphous and showed excellent solubility in common organic solvents, such as chloroform, tetrahydrofuran, xylene, toluene, chlorobenzene, and so forth. All possessed satisfied thermal stability with glass‐transition temperatures (T_g's) in the range of 79–115 °C. They emitted blue light with photoluminescent (PL) maximum peaks at about 408–412 nm in thin films. The PL efficiencies of the polymer films were measured around 30–33%. The highly phenylated pendants improved the T_g of polyfluorene without forming defects in the polymers and reduced their tendency to form aggregate/excimers. Polymer light‐emitting diodes were fabricated from these polymers with the configuration of indium tin oxide/polyethylenedioxythiophene:polystyrene sulfonic acid/polymer/Ba/Al, which emitted bright blue light with maximum peaks at 418–420 nm. The maximum external quantum efficiencies of these devices were 0.41–0.6%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2985–2993, 2004     

White electroluminescence from a single polymer: A blue‐emitting polyfluorene incorporating orange‐emitting benzoselenadiazole segments on its main chain

We have developed efficient white‐light‐emitting polymers through the incorporation of low‐bandgap orange‐light‐emitting benzoselenadiazole ( BSeD ) moieties into the backbone of a blue‐light‐emitting bipolar polyfluorene (PF) copolymer, which contains hole‐transporting triphenylamine and electron‐transporting oxadiazole pendent groups. By carefully controlling the concentrations of the low‐energy‐emitting species in the resulting copolymers, partial energy transfer from the blue‐fluorescent PF backbone to the orange‐fluorescent segments led to a single polymer emitting white light and exhibiting two balanced blue and orange emissions simultaneously. Efficient polymer light‐emitting devices prepared using this copolymer exhibited luminance efficiencies as high as 4.1 cd/A with color coordinates (0.30, 0.36) located in the white‐light region. Moreover, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study revealed that energy transfer from the PF backbone to the low‐bandgap segments, rather than charge trapping, was the main operating process involved in the electroluminescence process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2938–2946, 2007     

Synthesis,characterization, and electroluminescence of PPV copolymers containing electron and hole‐transporting units

Three series of poly(phenylene vinylene) (PPV) derivatives containing hole‐transporting triphenylamine derivatives [N‐(4‐octoxylphenyl)diphenylamine, N,N′‐di(4‐octyloxylphenyl)‐N,N′‐diphenyl‐1,4‐phenylenediamine, and N,N′‐di(4‐octoxylphenyl)‐N,N′‐diphenylbenzidine] (donor) and electron‐transporting oxadiazole unit (2,5‐diphenyl‐1,3,4‐oxadiazole) (acceptor) in the main chain were synthesized by improved Wittig copolymerization. The resulting donor–acceptor (D‐A) polymers are readily soluble in common organic solvents, such as chloroform, dichloroethane, THF, and toluene. The polymers containing oxadiazole group exhibit good thermal stability with 5% weight loss above 400 °C. The intramolecular charge‐transfer was observed in these D‐A polymers. In comparison with corresponding polymers without oxadiazole unit, the single‐layer devices based on the D‐A polymers showed much improved electroluminescent properties, because of the balanced charge injection and transport. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1566–1576, 2008     

Blue light‐emitting poly(p‐phenylenevinylene) derivatives containing alternating conjugated segments and aliphatic spacers

Two new poly(p‐phenylenevinylene) derivatives were prepared by Heck coupling. They contained alternating conjugated segments on the basis of p‐distyrylbenzene and flexible nonconjugated spacers. The synthesized polymers P1 and P2 carried two m‐terphenyl of four tertbutyl pendants, respectively, per repeat unit. Both polymers were amorphous and exhibited satisfactory thermal stability. Polymer P1 displayed a limited solubility in common organic solvents, whereas P2 dissolved readily in these solvents. The glass‐transition temperature values were 128 °C for P1 and 37 °C for P2 . The polymers emitted blue or violet‐blue light with photoluminescent maxima at about 445 and 460 nm for solutions and thin films, respectively. The bulky pendants reduced their tendency to form aggregates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1091–1098, 2003     

Novel thermally stable poly(amine hydrazide)s and poly(amine‐1,3,4‐oxadiazole)s for luminescent and electrochromic materials

We describe the preparation, characterization, and luminescence of four novel electrochromic aromatic poly(amine hydrazide)s containing main‐chain triphenylamine units with or without a para‐substituted N,N‐diphenylamino group on the pendent phenyl ring. These polymers were prepared from either 4,4′‐dicarboxy‐4″‐N,N‐diphenylaminotriphenylamine or 4,4′‐dicarboxytriphenylamine and the respective aromatic dihydrazide monomers via a direct phosphorylation polycondensation reaction. All the poly(amine hydrazide)s were amorphous and readily soluble in many common organic solvents and could be solution‐cast into transparent and flexible films with good mechanical properties. These poly(amine hydrazide)s exhibited strong ultraviolet–visible absorption bands at 346–348 nm in N‐methyl‐2‐pyrrolidone (NMP) solutions. Their photoluminescence spectra in NMP solutions or as cast films showed maximum bands around 508–544 and 448–487 nm in the green and blue region for the two series of polymers. The hole‐transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. All obtained poly(amine hydrazide)s and poly(amine‐1,3,4‐oxadiazole)s exhibited two reversible oxidation redox couples at 0.8 and 1.24 V vs. Ag/AgCl in acetonitrile solution and revealed excellent stability of electrochromic characteristics, changing color from original pale yellow to green and then to blue at electrode potentials of 0.87 and 1.24 V, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3245–3256, 2005     

Synthesis,characterization, and electroluminescence of novel copolyfluorenes and their applications in white light emission

New copolyfluorenes (PC8OF0–PC8OF50) comprised of 9,9‐dioctylfluorene and jacketed units 2,5‐bis[(5‐octyloxy‐phenyl)‐1,3,4‐ oxadiazole]‐1‐(3,5‐dibromophenyl)‐benzene (35C8) were synthesized by palladium‐catalyzed Suzuki coupling reaction. They were characterized by molecular weight determination, ¹H NMR, elemental analysis, DSC, TGA, absorption and emission spectroscopy, and cyclic voltammetry (CV). These copolymers were readily soluble in common organic solvents and exhibited high glass transition temperature and thermal stability.The copolymer films showed absorption peaks from 381 nm to 351 nm, and PL peaks from 432 nm to 421 nm with a blue shift originated from 35C8 units. Both the HOMO energy levels and LUMO levels changed little as the content of 35C8 units increased (?5.59 eV to ?5.48 eV and ?2.60 eV to ?2.49 eV). Electroluminescent devices: ITO/PEDOT:PSS[poly(ethylenedioxythiophene):polystyrenesulfonate]/polymer/Ca (25 nm)/Ag(80 nm) (a), ITO/PEDOT:PSS/polymer/TPBI [1,3,5‐ tris(N‐phenylbenzimidazol‐2‐yl)benzene](15 nm)/Mg:Ag(10:1, wt)/Ag (b), and ITO/ PEDOT:PSS/PVK[Poly(N‐vinylcarbazole)]/polymer/TPBI(15 nm)/Ca(25 nm)/Ag(80 nm) (c) were fabricated to investigate the influence of jacketed contents and device architectures on emission characteristics. The maximum brightness and current efficiency of the PC8OF25 device (5097.8 cd/m² and 0.484 cd/A) surpassed those of the PC8OF0 device (3122.8 cd/m² and 0.416 cd/A). The EL emissions of PC8OF0 – PC8OF50 were pure blue and low‐energy excimer emission bands were successfully suppressed, indicating that these copolymers could be good candidates for blue light‐emitting materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4555–4565, 2009     

Copolyfluorenes containing pendant bipolar carbazole and 1,2,4‐triazole groups: Synthesis,characterization, and optoelectronic applications

Three novel copolyfluorenes ( P1 ‐ P3 ) containing pendant bipolar groups (2.5–7.7 mol %), directly linked hole‐transporting carbazole and electron‐transporting aromatic 1,2,4‐triazole, were synthesized by the Suzuki coupling reaction and applied to enhance emission efficiency of polymer light‐emitting diodes based on conventional MEH‐PPV. The bipolar groups not only suppress undesirable green emission of polyfluorene under thermal annealing, but also promote electron‐ and hole‐affinity of the resulting copolyfluorenes. Blending the bipolar copolyfluorenes with MEH‐PPV results in significant enhancement of device performance [ITO/PEDOT:PSS/MEH‐PPV+ P1 , P2 or P3 /Ca(50 nm)/Al(100 nm)]. The maximum luminance and luminance efficiency were enhanced from 3230 cd/m² and 0.29 cd/A of MEH‐PPV‐only device to 15,690 cd/m² and 0.81 cd/A (blend device with MEH‐PPV/ P3 = 94/6 containing about 0.46 wt % of pendant bipolar residues), respectively. Our results demonstrate the efficacy of the bipolar copolyfluorenes in enhancing emission efficiency of MEH‐PPV. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(fluorenevinylene) derivatives by Heck coupling: Synthesis,photophysics, and electroluminescence

Three new poly(fluorenevinylene) derivatives were synthesized, characterized, and used as emissive materials in light‐emitting diodes (LEDs). They were synthesized by Heck coupling of 9,9‐dihexyl‐2,7‐divinylfluorene with 2,7‐dibromo‐9,9‐dihexylfluorene, 2,3‐bis(4‐bromophenyl)quinoxaline, or 2,5‐bis(4‐bromophenyl)‐3,4‐diphenylthiophene to afford the polymers F , Q , and T , respectively. Polymers F and Q had medium number–average molecular weights (M_n ? 14,000) with relatively narrow polydispersity (1.3–1.6), while T was obtained as an oligomer (M_n ? 4000). All polymers were soluble in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. They emitted blue‐greenish fluorescence light in dilute THF solution (444–491 nm), with photoluminescence (PL) quantum yields of 0.32–0.54, and in thin film (453–488 nm). LEDs with the configuration of ITO/PEDOT‐PSS/Polymer/Li:Al were fabricated and evaluated. The electroluminescence (EL) spectra of the Q and F polymers were very broad covering the blue–green–red region, whereas the spectrum of the polymer T was almost purely blue. The threshold electrical field for light emission of the devices was almost the same (?1.75 MV/cm). The external quantum efficiency of the devices of polymers Q and F was about 1.0 × 10^?3%, whereas that of polymer T was ?3.0 × 10^?5%. The fluorescence lifetime of polymers F and Q was significantly longer than that of the polymer T . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4494–4507, 2006     

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     

Highly substituted poly(2,3‐diphenyl‐1,4‐phenylenevinylene) derivatives having bulky phenyl and fluorenyl pendant groups: Synthesis,characterization, and electro‐optical properties

Two series of poly(2,3‐diphenyl‐1,4‐phenylenevinylene) (DP‐PPV) derivatives containing multiple bulky substituents were synthesized. In the first series, two different groups were incorporated on C‐5,6 positions of the phenylene moiety to increase steric hindrance and to obtain blue‐shifted emissions. In the second series, bulky fluorenyl groups with two hexyl chains on the C‐9 position were introduced on two phenyl pendants to increase the solubility as well as steric hindrance to prevent close packing of the main chain. Polymers with high molecular weights and fine‐tuned electro‐optical properties were obtained by controlling the feed ratio of different monomers during polymerization. The maximum photoluminescent emissions of the thin films are located between 384 and 541 nm. Cyclic voltammetric analysis reveals that the band gaps of these light‐emitting materials are in the range from 2.4 to 3.3 eV. A double‐layer EL device with the configuration of ITO/PEDOT/P4/Ca/Al emitted pure green light with CIE′1931 at (0.24, 0.5). Using copolymer P6 as the emissive layer, the maximum luminescence and current efficiency were both improved when compared with the homopolymer P4. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6738–6749, 2006