Vinyl copolymers containing pendant 1,4‐distyrylbenzene and 1,3,4‐oxadiazole chromophores: Preparation and optoelectronic properties

We prepared two vinyl copolymers P1 and P2 containing pendant distyrylbenzene and aromatic 1,3,4‐oxadiazole derivatives, respectively, from their precursor poly(styrene‐ran‐4‐vinylbenzyl chloride) (M_w = 11,400, PDI = 1.18), which had been prepared by the controlled radical polymerization (RAFT). Two main chain polymers containing similar isolated distyrylbenzene ( P3) and aromatic 1,3,4‐oxadiazole ( P4 ) chromophores were also synthesized for comparative study. The resulted copolymers ( P1 – P4 ) are soluble in common organic solvents and are basically amorphous materials with 5% weight‐loss temperature higher than 360 °C. The PL spectral results reveal that the architecture of P1 prevents the formation of inter‐ or intramolecular interaction. The HOMO and LUMO levels of P2 , estimated from cyclic voltammetric data, are ?5.96 and ?3.81 eV, respectively, which are much lower than those of P1 (?5.12 and ?3.11 eV). The emission of blend from P1 and P2 are contributed mainly from distyrylbenzene fluorophore (～450 nm) owing to efficient energy transfer. Moreover, the blend exhibits three kinds of redox behavior depending on their weight ratios. The luminance and current efficiency of the EL device lpar;ITO/PEDOT/ MEH ‐ PPV + P2 /Al) are 503 cd/m² and 0.11 cd/A, which can be improved to 1285 cd/m² and 0.44 cd/A, respectively, as the weight ratio of P2 increases from 0 to 20%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5362–5377, 2006     

Hyperbranched copolyfluorene from a 2,4,7‐trifunctional fluorene monomer

A new hyperbranched ( P1 ) and linear copolyfluorene ( P2 ) were prepared from 2,4,7‐trifunctional (branching) and 2,7‐bifunctional fluorene monomer, respectively, by the Wittig reaction, followed with end‐capping by aromatic oxadiazole groups, to study the effect of hyperbranch structure. The weight‐average molecular weights (M_w) of P1 and P2 , determined by gel permeation chromatography using polystyrene as standard, were 33,000 and 25,700, respectively. The polymers were readily soluble in common organic solvents and exhibited good thermal stability (T_d > 400 °C). Optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. In film state, the absorption and PL spectra peaked at 401–425 nm and 480–495 nm, respectively. The P1 showed energy funnel effect and enhanced fluorescence efficiency owing to hyperbranched structure and terminal oxadiazole groups. The HOMO and LUMO levels of P1 ( P2) , estimated from cyclic voltammograms, are ?5.34 (?5.25) eV and ?2.94 (?2.94) eV, respectively. Two‐layer polymer light‐emitting diodes devices (ITO/PEDOT/ P1 /Ca/Al) exhibited maximal luminance and luminous efficiency of 3630 cd/m² and 0.78 cd/A, respectively, which are superior to its linear counterpart P2 (598 cd/m², 0.11 cd/A). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5541–5551, 2007     

Luminescent copoly(aryl ether)s with new electron‐transporting bis(3‐(trifluoromethyl)phenyl)‐1,3,4‐oxadiazole or bis(3‐(trifluoromethyl)phenyl)‐4‐(4‐hexyloxyphenyl)‐4H‐1,2,4‐triazole segments

To investigate the effect of trifluoromethyl groups in enhancing electron affinity of aromatic oxadiazole and triazole chromophores, we prepared four new copoly(aryl ether)s ( P1 – P4 ) consisting of bis(3‐(trifluoromethyl) phenyl)‐1,3,4‐oxadiazole (ETO) or bis(3‐(trifluoromethyl)phenyl)‐4‐(4‐hexyloxyphenyl)‐4H‐1,2,4‐triazole (ETT) segments and hole‐transporting segments [2,5‐distyrylbenzene (HTB) or bis(styryl)fluorine (HTF)]. Molecular spectra (absorption and photoluminescence) and cyclic voltammetry were used to investigate their optical and electrochemical properties. The emissions of P1 – P4 are dominated by the hole‐transporting fluorophores with longer emissive wavelengths around 442–453 nm via efficient excitation energy transfer. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of P1 – P4 , estimated from electrochemical data, are ?5.15, ?5.18, ?5.30, ?5.27, ?3.39, ?3.49, ?3.36, and ?3.48 eV, respectively. The LUMO levels of ETO and ETT segments are significantly reduced to ?3.39～?3.36 eV and ?3.48～?3.49 eV, respectively, as compared with ?2.45 eV of P5 containing a 2,5‐diphenyl‐1,3,4‐oxadiazole segment. Moreover, electron and hole affinity can be enhanced simultaneously by introducing isolated hole‐ and electron‐transporting segments in the backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5900–5910, 2004     

Novel mesogen‐jacketed poly(p‐phenylenevinylene) derivatives bearing oxadiazole pendants: Design,synthesis, and optoelectronic properties

1,3,4‐oxadiazole moieties were laterally linked to the phenyl rings via a short ? OCH₂ spacer and a series of novel poly(p‐phenylenevinylene) derivatives have been successfully synthesized through Horner–Witting–Emmons coupling reaction. The structures and properties of the monomers and the resulting conjugated polymers were characterized by nuclear magnetic resonance spectroscope, Fourier transform infrared, elemental analysis, gel permeation chromatography, thermogravimetric analysis, UV–vis absorption (UV) spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. The UV spectra at solution state was similar to what's observed at film state while the PL spectra at film state had a red shift from 19 to 28 nm compared with the results at solution state, which implied that the unique bulky jacketed structure containing oxadiazole unit of these copolymers could effectively suppress π‐stacking/aggregation. LUMO levels of these polymers varied from ?3.44 to ?3.63 eV with increasing content of oxadiazole units, which facilitated electron injection. PLEDs with the configuration of ITO/PEDOT/Polymer/TPBI (15 nm)/LiF (1 nm)/Al (100 nm) were fabricated, which emit a yellowish green light around 540 and 570 nm with a maximum brightness of 1074.7 cd/m² and luminous efficiency of 0.108 cd/A. The introduction of the unique bulky OXD unit into PPVs at a low molar content largely improved the electroluminescence properties of PPV. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7173–7186, 2008     

Synthesis of electroluminescent copoly(aryl ether)s containing alternate 1,4‐distyrylbenzene derivatives and aromatic 1,3,4‐oxadiazole or 3,3″‐terphenyldicarbonitrile segments

New copoly(aryl ether)s ( P1 – P3 ) containing alternate 2,5‐dihexyloxy‐1,4‐di(m‐ethoxystyryl)benzene ( P1 , P2 ) or 2,5‐dihexyloxy‐1,4‐distyrylbenzene ( P3 ) chromophores and aromatic 1,3,4‐oxadiazole ( P1 ) or 3,3″‐terphenyldicarbonitrile ( P2 , P3 ) segments were prepared by Horner reaction ( P1 and P2 ) or nucleophilic displacement reaction ( P3 ). They are basically amorphous materials with 5% weight‐loss temperature above 410 °C. Their absorption, photoluminescence spectra, and quantum yields are dependent on the composition of the isolated fluorophores. The emissions are exclusively dominated by 1,4‐distyrylbenzene segments via excitation energy transfer from electron‐transporting 1,3,4‐oxadiazole ( P1 ) or 3,3″‐terphenyldicarbonitrile ( P2 , P3 ) chromophores. The HOMO and LUMO energy levels have been estimated from their cyclic voltammograms, and the observations confirm that oxidation and reduction start from the emitting 1,4‐distyrylbenzene and electron‐transporting segments, respectively, indicating that both carriers affinity can be enhanced simultaneously. Among the two‐layer PLED devices (ITO/PEDOT/ P1 – P3 /Al), P1 exhibits the best performance with a turn‐on field of 4 × 10⁵ V/cm and a maximum luminance of 225 cd/m². However, P2 emits green–yellow light (555 nm), owing to the excimer emission. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5009–5022, 2005     

Optical and electrochemical properties of copoly(aryl ether)s consisting of alternate 2,5‐distyrylbenzene and electron‐transporting oxadiazole or triazole derivatives

New copoly(aryl ether) P1 consisting of alternate electron‐transporting 2‐(3‐(trifluoromethyl)phenyl)‐5‐(4‐(5‐(3‐(trifluoromethyl)phenyl)‐1,3,4‐oxadiazol‐2‐yl)‐2,5‐bis(hexyloxy)phenyl)‐1,3,4‐oxadiazole and hole‐transporting 2,5‐distyrylbenzene (DSB) was synthesized via nucleophilic substitution polymerization. We investigated the optical and electrochemical properties of alternate copoly(aryl ether)s P1 – P6 , which contain the same hole‐transporting DSB segments, but with different electron transporting segments. The effect of trifluoromethyl groups in electron transporting segments is also discussed. Referencing to the spectra of their model compounds M1 – M4 , the emissions of P1 – P3 are dominated exclusively by the hole‐transporting fluorophores with longer emissive wavelength about 452–453 nm via efficient excitation energy transfer. Furthermore, P1 – P3 also exhibit unique variations in energy transfer in acidic media and solvatochromism in organic solvents. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of P1 – P4 , estimated from electrochemical data, are ?5.12, ?5.15, ?5.18, ?5.00 eV and ?2.93, ?3.39, ?3.49, ?2.76 eV, respectively. The electron and hole affinity of P1 – P6 can be enhanced simultaneously by introducing isolated hole‐ and electron‐transporting segments in backbone. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5083–5096, 2005     

Linear π‐conjugated polymers containing 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit: Synthesis and optical properties

Some linear π‐conjugated polymers containing 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit were synthesized via Sonogashira or Suzuki reaction for the first time and characterized by IR, NMR, and GPC. Because of the introduction of 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit into π‐conjugated system, all polymers exhibited good thermal stability with high decomposition temperature. Their optical and electrochemical properties were investigated. Based on the 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit linked with different aromatic rings, the polymers showed the tunable fluorescence from blue to blue‐green emission with satisfied quantum yield. Cyclic voltammetry measurement indicated that the LUMO and HOMO levels of the polymers could be adjustable through the main‐chain structural modification. All polymers had low LUMO level (?2.86 to ?3.06 eV) due to the high‐electron affinity of triazine unit. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 702–712, 2008     

Vinyl copolymers containing pendant 1,3,4-oxadiazole chromophores: Preparation and electrochemical and electroluminescent properties

Three vinyl copolymers (P1–P3) containing pendant aromatic 1,3,4-oxadiazole derivatives were prepared from their precursor poly(styrene-ran-4-vinylbenzyl chloride) (weight-average molecular weight = 11,400, polydispersity index = 1.18), which had been synthesized by controlled radical polymerization (reversible addition–fragmentation chain transfer). The copolymers were readily soluble in common organic solvents and were basically amorphous materials with 5% weight loss temperatures higher than 360°C. The photoluminescence spectroscopy results revealed that the architectures of P2 and P3 suppressed aggregate formation in the solid state. The LUMO levels of P2 (−3.10 eV) and P3 (−3.09 eV), estimated from cyclic voltammetry data, were much higher than that of P1 (−3.81 eV). The HOMO levels were in the order of P3 (−5.37 eV) > P2 (−5.77 eV) > P1 (−5.96 eV). However, both the HOMO and LUMO levels of P1–P3 were much lower than that of poly[2-methoxy-5-(2′-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) because of the electron-withdrawing characteristics of the pendant aromatic 1,3,4-oxadiazole groups. The luminance (5860 cd/m²) and current efficiency (1.45 cd/A) of an electroluminescence device [indium tin oxide/poly(3,4-ethylene dioxythiophene)/MEH-PPV/Al] were improved significantly to 16,261 cd/m² and 4.79 cd/A, respectively, through blending with P2 (50/50). This study suggests that copolymers P1–P3 are versatile materials for electron-transport/injection applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2259–2272, 2007     

Crosslinkable poly(p‐phenylenevinylene) derivative

To simplify the fabrication of multilayer light‐emitting diodes, we prepared a p‐phenylenevinylene‐based polymer capped with crosslinkable styrene through a Wittig reaction. Insoluble poly(p‐phenylenevinylene) derivative (PPVD) films were prepared by a thermal treatment. The photoluminescence and ultraviolet–visible (UV–vis) absorbance of crosslinked films and noncrosslinked films were studied. We also studied the solvent resistance of crosslinked PPV films with UV–vis absorption spectra and atomic force microscopy. Double‐layer devices using crosslinked PPVD as an emitting layer, 2‐(4‐tert‐butylphenyl)‐5‐phenyl‐1,3,4‐oxadiazole (PBD) in poly(methyl methacrylate) as an electron‐transporting layer, and calcium as a cathode were fabricated. A maximum luminance efficiency of 0.70 cd/A and a maximum brightness of 740 cd/m² at 16 V were demonstrated. A 12‐fold improvement in the luminance efficiency with respect to that of single‐layer devices was realized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2124–2129, 2004     

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     

Conjugated copolymers comprised cyanophenyl‐substituted spirobifluorene and tricarbazole‐triphenylamine repeat units for blue‐light‐emitting diodes

A series of conjugated blue‐light‐emitting copolymers, PTC‐1 , PTC‐2 , and PTC‐3, comprised different ratios of electron‐withdrawing segments (spirobifluorene substituted with cyanophenyl groups) and electron‐donating segments (tricarbazole‐triphenylamines), has been synthesized. The structures of these polymers were characterized and their thermal, photophysical, electrochemical, and electroluminescence properties were measured. Incorporation of rigid spirobifluorene units into the copolymers led to blue‐shifted absorption peaks in dilute toluene solution. Cyclic voltammetric measurement indicated the bandgaps of the polymers were in the range of 2.77–2.94 eV. It was found that increasing cyanophenyl‐spirobifluorene content in the polymer backbone lowered both the HOMO and LUMO energy levels of the copolymers, which was beneficial for electron injection/transporting in the polymer layer of the device. OLED device evaluation indicated that all the polymers emitted sky blue to deep blue light when the pure polymers were used as the emissive layers in the devices with a configuration of ITO/PEDOT:PSS/polymers/CsF/Ca/Al. The devices have been optimized by doping 30 wt % PBD into the polymer layers. Among the doped devices, PTC‐2 showed the best performance with the turn‐on voltage of 3.0 V, maximum brightness of 7257 cd/m², maximum current efficiency of 1.76 cd/A, and CIE coordinates of (0.15, 0.14). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 292–301, 2010     

Soluble polynorbornenes with pendant carbazole derivatives as host materials for highly efficient blue phosphorescent organic light‐emitting diodes

We report novel host polymers for a high‐efficiency polymer‐based solution‐processed phosphorescent organic light‐emitting diode with typical blue‐emitting dopant bis(4,6‐difluorophenylpyridinato‐N,C²)iridium(III) picolinate (FIrpic). The host polymers, soluble polynorbornenes with pendant carbazole derivatives, N‐phenyl‐9H‐carbazole ( P1 ), N‐biphenyl‐9H‐carbazole ( P2 ), and 9,9′‐(1,3‐phenylene)bis‐9H‐carbazole (mCP) ( P3 ) are efficiently synthesized by vinyl addition polymerization of norbornene monomers using Pd(II) catalyst in combination with 1‐octene chain transfer agent. The polymers exhibit high thermal stability with high decomposition (T_d5 > 410 °C) and glass transition temperatures (T_g ≈ 268 °C). The HOMO (ca. ?5.5 to ?5.7 eV) and LUMO (ca. ?2.0 to ?2.1 eV) levels with the high triplet energy of about 2.7–3.0 eV suggest that the polymers are suitable for a host material for blue emitters. Among the solution‐processed devices that were fabricated based on the emissive layers containing the P1 ? P3 host doped with various concentrations of FIrpic (7–13 wt %), the best device with P3 host exhibits power efficiency of 3.0 lm W^?1 and external quantum efficiency of 4.0% at a luminance of 1000 cd m^?2 that is outstanding among the polymeric rivals. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Hyperbranched and thermally cross‐linkable oligomer from a new 2,5,7‐tri‐functional fluorene monomer

New hyperbranched (HOFV) and linear oligomers (LOFV) were prepared from 2‐bromo‐5,7‐divinyl‐9,9‐dihexylfluorene (AB₂) and 2‐bromo‐7‐vinyl‐9,9‐dihexylfluorene, respectively, by the Heck reaction to study the effect of hyperbranched structure. The oligomers were readily soluble in common organic solvents. The weight‐average molecular weights (M_w) of HOFV and LOFV, determined by gel permeation chromatography using polystyrene as standard, were 2350 and 3950, respectively. Optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. In film state, the absorption and PL spectra peaked at 416 ～ 425 nm and 473 ～ 503 nm, respectively. The HOFV showed energy funnel effect and enhanced fluorescence efficiency owing to the hyperbranched structure. The HOMO and LUMO levels of HOFV (LOFV), estimated from their cyclic voltammograms, were ?5.25 (?5.34) eV and ?2.66 (?2.75) eV, respectively. Thermal curing of HOFV to form cross‐linked HPFV (hyperbranched poly(fluorenevinylene)) was studied by IR, DSC, UV–visible spectra, NMR, AFM and SEM. The terminal vinyl groups in HOFV film almost disappeared to provide smooth, homogeneous and solvent‐resistant films of HPFV. Two‐layer PLED devices (ITO/PEDOT/HPFV/Ca/Al) exhibited maximal luminance and luminous efficiency of 1480 cd/m² and 0.18 cd/A, respectively, which were superior to its linear counterpart LPFV (352 cd/m², 0.06 cd/A). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 70–84, 2008     

Preparation and properties of oxadiazole‐containing polyacetylenes as electron transport materials

A series of functional polyacetylenes (PAs) bearing diphenyl oxadiazole pendant groups ( P1 – P4 ) were prepared, and the resultant polymers are completely soluble in common organic solvents. Their structures and properties were characterized and evaluated by DSC, TGA, UV, PL, CV, and EL analyses. The results show that all the resulting polymers possesses low LUMO energy level and high thermal stability, and the resultant functional polyacetylenes without spacer group between the polyacetylene conjugated main chain and oxadiazole pendant groups ( P1 – P3 ) show lower LUMO energy level (～?3.87 eV) and higher thermal properties (T_g) than that ( P4 ) with a flexible spacer. The resultant polymer ( P2 ) was applied as an ETM in bilayer electroluminescent devices and effectively enhances external quantum efficiency and the brightness of device, and decreases turn‐on voltages of devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1406–1414, 2010     

Synthesis and characterization of luminescent polyethers with 2,5‐distyrylthiophene and aromatic oxadiazole chromophores

Two new luminescent copolyethers ( P1 and P2 ) with isolated 2,5‐distyrylthiophene‐emitting segments and electron‐transporting 2,5‐diphenyl‐1,3,4‐oxadiazole chromophores were successfully synthesized by the Horner–Wadworth–Emmons reaction. The solubility, optical, and electrochemical properties of the polymers were investigated and correlated with nonlinear thiophene and 1,3,4‐oxadiazole groups. P2 with pendant 1,3,4‐oxadiazole was soluble in common organic solvents such as chloroform, tetrahydrofuran, and C₂H₂Cl₄. Thermogravimetric analysis and differential scanning calorimetry showed that the copolyethers were thermally stable below 345 °C, with glass‐transition temperatures higher than 110 °C. They were yellow‐greenish emitting materials with a band gap of 2.57–2.58 eV estimated from the onset absorption. Incorporating the thiophene moiety narrowed the band gaps of the copolyethers. The photophysical and electronic properties of the polymer and the preliminary electroluminescent device made from the polymer demonstrate that the polymer may be a potential candidate material for the fabrication of polymeric light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2927–2936, 2002     

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     

Single layer light‐emitting diodes from copolymers comprised of mesogen‐jacketed polymer containing oxadiazole units and PVK

A series of copolymers PCt‐co‐Poly(N‐vinylcarbazole) were synthesized through common radical polymerization, in which P‐Ct as a kind of mesogen‐jacketed liquid crystalline polymer was introduced, and the effects of copolymers composing variation on the optical properties of the polymers were studied. The structures and properties of the copolymers were characterized and evaluated by thermogravimetric (TGA), UV, photoluminescence (PL), cyclic voltammetry (CV), and electroluminescence (EL) analyses. All the polymers enjoy high thermal stability. PL peaks in the film show blue‐shift compared with in solutions and fluorescent quantum efficiency decreased with the N‐vinylcarbazole (nvk) content increasing, which supported the efficient energy transfer from nvk units to the oxadiazole units. CV revealed that, with the incorporation of nvk to the copolymer, these copolymers had high‐lying HOMO energy levels ranging from ?5.94 to ?6.09 eV. Single‐layer light‐emitting diodes (LEDs) with the configuration of ITO/PEDOT/PCt‐nvk/Mg:Ag/Ag were fabricated, which emit a blue light around 450 and 490 nm with a maximum luminance of 703 cd/m². The device performance varies with the content of nvk and device configuration, with device configuration ( b ) and PCt‐nvk8 giving the best value of external quantum efficiency of 0.27%. We show here that by proper design copolymer structure and modification of device configuration can exhibit strong blue EL in higher external quantum efficiency. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1843–1851, 2008     

Low bandgap π‐conjugated copolymers based on fused thiophenes and benzothiadiazole: Synthesis and structure‐property relationship study

A series of low bandgap conjugated polymers consisting of benzothiadiazole alternating with dithienothiophene (DTT) or dithienopyrrole (DTP) unit with or without 3‐alkylthiophene bridge have been synthesized. Effect of the fused rings and 3‐alkylthiophene bridge on the thermal, optical, electrochemical, charge transport, and photovoltaic properties of these polymers have been investigated. These polymers show broad absorption extending from 300 to 1000 nm with optical bandgaps as low as 1.2 eV; the details of which can be varied either by incorporating 3‐alkylthiophene bridge or by replacing DTT with DTP. The LUMO levels (?2.9 to ?3.3 eV) are essentially unaffected by the specific choice of donor moiety, whereas the HOMO levels (?4.6 to ?5.6 eV) are more sensitive to the choice of donor. The DTT and DTP polymers with 3‐alkylthiophene bridge were found to exhibit hole mobilities of 8 × 10^?5 and 3 × 10^?2 cm² V^?1 s^?1, respectively, in top‐contact organic field‐effect transistors. Power conversion efficiencies in the range 0.17–0.43% were obtained under simulated AM 1.5, 100 mW cm^?2 irradiation for polymer solar cells using the DTT and DTP‐based polymers with 3‐alkylthiophene bridge as donor and fullerene derivatives as acceptor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5498–5508, 2009     

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 characterization of novel poly(p‐phenylenevinylene) derivatives containing phenothiazine‐5‐oxide and phenothiazine‐5, 5‐dioxide moieties

PPV‐based copolymers containing phenothiazine‐5‐oxide and phenothiazine‐5, 5‐dioxide moieties have been successfully synthesized by Wittig‐Horner reaction and characterized by means of UV‐vis, photoluminescence, electroluminescence spectra, and cyclic voltammetry. All of these copolymers can be dissolved in common organic solvents such as chloroform, tetrahydrofuran, and toluene. The PL maxima in the film state are located at 582, 556, and 552 nm for P1, P2, and P3, respectively. The HOMO and LUMO levels of P2 are found to be ?5.21 and ?2.68 eV, respectively; whereas those of P3 are found to be ?5.26 and ?2.71 eV, respectively. The cyclic voltammetry result indicates that the conversion of electron‐donating sulfide to electron‐withdrawing sulfoxide or sulfone group in polymers plays a dominating role in increasing its oxidation potential. Yellowish‐green light ranging from 568 to 540 nm was observed for the single layer device with the configuration of ITO/Polymer/Ca/Al. Double layer devices with Zn (BTZ)₂ as a hole blocking layer exhibited enhanced EL performance compared to the single layer devices. The maximum brightness of the double layer devices of P1, P2, and P3 is 278, 400, and 796 cd/m², respectively. The results of EL and electrochemical analyses revealed that they are promising candidate materials for organic, light‐emitting diodes with hole‐transporting ability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4291–4299, 2007