Aggregation-enhanced emission and efficient electroluminescence of conjugated polymers containing tetraphenylethene units

Tetraphenylethene (TPE) is a popular luminogen characterized by aggregation-induced emission and has been widely used to construct solid-state emissive materials. In this work, two thermally stable polymers (P1 and P2) consisting of TPE conjugated to the 2,7-positions of fluorene and carbazole, respectively, are synthesized and characterized. Both polymers are weakly fluorescent in solutions but show greatly enhanced emission as the aggregate formation, presenting an aggregation-enhanced emission feature. Two kinds of polymer light-emitting diodes are fabricated utilizing P1 and P2 as emitters (EML) (device I: ITO/PEDOT:PSS (45 nm)/PVK:EML (1:1 wt%, 55 nm)/TPBI (38 nm)/Ca:Ag; device II: ITO/PEDOT:PSS (45 nm)/ PVK:OXD-7:EML (3:1:3 wt%, 55 nm)/TPBI (38 nm)/Ca:Ag). The device II of P2 shows the best performances, affording a maximum luminance of 6500 cd/m 2 and a high peak efficiency of 2.11 cd/A.     

High-performance blue electroluminescent devices based on 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-oxadiazole

An electron transporting moiety (1,3,4-oxadiazole) and a hole transporting moiety (carbazole) were combined to create 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-oxadiazole (CzOxa), a three layer device with a configuration of ITO/TPD(50 nm)/CzOxa(40 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm) which exhibited a blue emission peak at approximately 470 nm (x = 0.14, y = 0.19) with a maximum luminance of 26,200 cd m(-2) at a drive voltage of 15 V and a maximum luminous efficiency of 2.25 lm W(-1).     

Carbazolevinylene‐based polymers and model compounds with oxadiazole and triphenylamine segments: Synthesis,photophysics, and electroluminescence

Two new soluble alternating carbazolevinylene‐based polymers POXD and PTPA as well as the corresponding model compounds MOXD and MTPA were synthesized by Heck coupling. POXD and MOXD contained 2,5‐diphenyloxadiazole segments, while PTPA and MTPA contained triphenylamine segments. All samples displayed high thermal stability. The polymers had higher glass transition temperature (T_g) than their corresponding model compounds. The samples showed absorption maximum at 364–403 nm with optical band gap of 2.62–2.82 eV. They emitted blue‐green light with photoluminescence (PL) emission maximum at 450–501 nm and PL quantum yields in THF solution of 0.15–0.36. The absorption and the PL emission maxima of PTPA and MTPA were blue‐shifted as compared to those of POXD and MOXD . The electroluminescence (EL) spectra of multilayered devices made using four materials exhibited bluish green emissions, which is well consistent with PL spectra. The EL devices made using poly(vinyl carbazole) doped with MOXD and MTPA as emitting materials showed luminances of 12.1 and 4.8 cd m^?2. POXD and PTPA exhibited 25.4, and 96.3 cd m^?2, respectively. The polymer containing the corresponding molecules in the repeating group showed much higher device performances. Additionally, POXD and MOXD exhibited better stability of external quantum efficiency (EQE) and luminous efficiency with current density resulting from enhancing the electron transporting properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5592–5603, 2008     

Synthesis and characterization of new poly(aryl ether)s with isolated fluorophores

Four novel poly(aryl ether)s ( P1 – P4 ) consisting of alternate isolated electron‐transporting (3,3″′‐bis‐trifluoromethyl‐p‐quaterphenyl for P1 , P3 or 3,3″′‐dicyano‐p‐quaterphenyl for P2 , P4 ) and hole‐transporting fluorophores [N‐(2‐ethylhexyl)‐3,6‐bis(styryl)carbazole for P1 , P2 or 9,9‐dihexyl‐2,7‐bis(styryl)fluorene for P3 , P4 ] were synthesized and characterized. These poly(aryl ether)s can be dissolved in organic solvents and exhibited good thermal stability with 5% weight‐loss temperature above 500 °C in nitrogen atmosphere. The photoluminescent (PL) spectra of the films of these polymers showed maximum peaks at around 442–452 nm. The PL spectral results revealed that the emission of polymers was dominated by the fluorophores with longer emissive wavelength via the energy transfer from p‐quaterphenyl to 3,6‐bis(styryl)carbazole or 2,7‐bis(styryl)fluorene segments. Therefore, the p‐quaterphenyl segments function only as the electron‐transporting/hole‐blocking units in these polymers, and the other segments are the emissive centers and hole‐transporting units. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy levels of these polymers were measured by cyclic voltammetry. The electron‐donating nitrogen atom on carbazole resulted in the higher HOMO energy levels of P1 and P2 than those of P3 and P4 . The single‐layer light‐emitting diodes (LED) of Al/poly(aryl ether)s ( P1 – P4 )/ITO glass were fabricated. P1 , P2 , and P4 revealed blue electroluminescence, but P3 emitted yellow light as a result of the excimer emission. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2215–2224, 2002     

Synthesis and characterization of new blue‐light‐emitting polymers based on PPP and PPV having fluorene pendant at vinyl bridge

The new poly(arylene vinylene) derivatives, which are composed of biphenylene vinylene phenylene vinylene, biphenylene vinylene m‐phenylene vinylene, terphenylene vinylene phenylene vinylene, and terphenylene vinylene m‐phenylene vinylene as backbone and bulky fluorene pendants at each vinyl bridge, were designed, synthesized, and characterized. The obtained polymers showed weight‐average molecular weights of 11,100–39,800 with polydispersity indexes ranging from 1.5 to 2.1. The resulting polymers were amorphous with high thermal stability and readily soluble in common organic solvents. The obtained polymers showed blue emission (λ_max = 456–475 nm) in PL spectra, and polymer 4 containing terphenylene vinylene m‐phenylene vinylene showed the most blue shifted blue emission (λ_max = 456 nm). The double layer light‐emitting diode devices fabricated by using obtained polymers as emitter emitted bright blue light. The device showed turn on voltage around 6.5 V and brightness of 70–250 cd/m². © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4923–4931, 2006     

Synthesis of pure blue emissive poly(2,7‐carbazole)s anchored by electron donor pendant

Three novel poly(2,7‐carbazole)s having hole injection and transporting pendent moieties of carbazole and triphenylamine at the N‐position were synthesized for achieving pure blue electroluminescence. The N‐pendants in the polymers correspond to N‐phenylcarbazol‐2‐yl ( P1 ), N,N‐diphenylamino‐N‐phenylcarabazol‐2‐yl ( P2) , and 4‐phenyl having a hydrocarbon chain with a triphenylamine terminal ( P3 ), respectively. Electronic, optical, and electroluminescence properties of these polymers were compared with those of a poly(2,7‐carbazole) directly connected with triphenylamine at the N‐position ( P0 ) having an aggregation‐induced emissive property. The photoluminescence (PL) spectra suggested that they could emit in the region of blue light in the film state. Especially, P2 that has the fixed and large diphenylaminocarbazolyl pendant showed a deep‐blue fluorescence with CIE(x, y) = (0.15, 0.07). The P0 , P2 , and P3 based light emitting diode devices showed maximum electroluminescence wavelengths in the range of 430–450 nm. The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]), high luminance (1130 cd/m²) and current density (628 mA/cm²) at 8 V, whereas low‐energy emissions around 500–600 nm were emerged at higher than 9 V. The P0 and P3 devices also showed a blue electroluminescence in the range of 8–11 V, but their luminance and efficiency were low. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2526–2534     

N-苯基咔唑取代的蓝光聚(2,7-咔唑)的合成与表征

采用Suzuki聚合方法并通过改变催化剂的投料量,合成了一系列具有不同分子量的N-苯基咔唑取代的蓝光聚(2,7-咔唑),并详细研究了分子量对聚合物的光物理、电化学和电致发光器件性质的影响.结果表明,刚性N-苯基咔唑侧链的引入,能够有效地调控主链之间的相互作用,提高蓝光的色纯度,并使得该系列聚合物的固态荧光量子效率高达0.40.同时,在热退火及器件工作过程中,没有观察到类似聚芴中绿光峰的出现,表明具有良好的光谱稳定性.单层聚合物电致发光器件的最大发光效率为0.33 cd/A,色坐标为(0.18,0.12).     

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     

Phenothiazine‐S,S‐dioxide‐ and fluorene‐based light‐emitting polymers: Introduction of e−‐deficient S,S‐dioxide into e−‐rich phenothiazine

A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by ¹H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO₂ unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007     

New ladder‐type conjugated polymer containing carbazole and fluorene units in backbone: Synthesis,optical, and electrochemistry properties

This article describes the synthesis and characterization of a new ladder‐type poly (p‐phenylene) (LPFC) containing alkylcarbazole and dialkylfluorene units in backbone, and its optical and electrochemical properties as well as its light‐emitting device performance. LPFC shows the well‐defined structure, high molecular weights, excellent thermal stability, and good solubility in common organic solvents. And it also shows strongly blue emission (λ_max = 465 nm) with quantum efficiency of 70% in solution, while its solid emission (λ_max = 470 nm) is almost the same as its solution. Electrochemical studies show that the highest occupied molecular orbital (HOMO) energy levels of LPFC is up to 5.29 eV, which is significantly higher than that of LPPP without carbazole in backbone, indicating an enhanced ability of hole injection from anodes. Furthermore, the single layer light‐emitting device using LPFC as the active layer shows blue emission (λ_max = 470 nm) with maximum luminescence of ～ 2000 cd/m² and maximum luminance efficiency of 0.43 cd/A. The attractive properties exhibited from new ladder‐type polymer establish LPFC as a good candidate for the potential application as transporting and emitting layer in polymeric light emitting diodes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3120–3127, 2008     

Fluorene pendant-functionalization of poly(N-vinylcarbazole) as deep-blue fluorescent and host materials for polymer light-emitting diodes

π-Electron coupling of pendant conjugated segment in π-stacked semiconducting polymers always causes the formation of defect trapped sites and further quenched high-band excitons, which is harmful to the performance and stability of deep-blue polymer light-emitting diodes (PLEDs). Herein, considerate of “defect” carbazole (Cz) electromers in poly(N-vinylcarbazole) (PVK), a series of fluorene units are introduced into pendant segments (PVCz-DMeF, PVCz-FMeNPh and PVCz-DFMeNPh) to suppress the strong π-electron coupling of pendant Cz units and enhance radiative transition toward fabricating sable PLEDs. Compared to PVCz-FMeNPh and PVCz-DFMeNPh, PVCz-DMeF spin-coated films show a relatively efficient deep-blue emission, completely similar to its single pendant chromophore, confirmed an extremely weak charge-transfer and electron coupling between adjacent pendant segments. Therefore, PLEDs based on PVCz-DMeF present stable and deep-blue emission with a high color purity (0.17, 0.08), associated with extremely weak defect emission at 600∼700 nm (induced by carbazole electromers). Finally, PLEDs based on PVCz-DMeF/F8BT blended films (1:1) also present the high maximum luminance (L_max) of 6261 cd/m² and current efficiency (CE_max) of 2.03 cd/A, confirmed slightly trapped sites formation. Therefore, precisely control the arrangement and packing model of pendant units in π-stacked polymer is an essential prerequisite for building efficient and stable emitter for optoelectronic devices.     

Synthesis and properties of conjugated copolycondensates consisting of carbazole‐2,7‐diyl and fluorene‐2,7‐diyl

Carbazole and fluorene‐based random and alternating copolycondensates were synthesized to develop high‐performance blue light‐emitting polymers by improving electron injection ability of poly(N‐aryl‐2,7‐carbazole)s that showed intense blue electroluminescence (EL) with good hole‐injection and ‐transport ability. These copolycondensates absorbed light energy at about λ_max = 390 nm in CHCl₃ and 400 nm in film state, and fluoresced at about λ_max = 417 nm in CHCl₃ and 430 nm in the thin film state. Energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of them were about 2.9 eV, and the energy levels of LUMO situated lower than that of corresponding polycarbazole. Polymer light‐emitting diode devices having configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)/polymer/CsF/Al using the copolycondensates, poly(N‐arylcarbazole‐2,7‐diyl), and poly(9,9‐dialkylfluorene‐2,7‐diyl), emitted bluish EL at operating voltages lower than 7 V. The device embedded the random copolycondensate showed notably higher performance with maximum luminance of 31,200 cd m^?2 at 11.0 V, and the current efficiencies observed under operating voltages lower than 7 V were higher than those of the other devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and properties of nitrogen‐linked poly(2,7‐carbazole)s as hole‐transport material for organic light emitting diodes

A novel class of carbazole polymers, nitrogen‐linked poly(2,7‐carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium‐catalyzed amination reaction. The polymers were characterized by ¹H NMR, Infrared, Gel permeation chromatography, and MALDI‐TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2 . To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV‐Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of ?5.12 to ?5.20 eV. Therefore, light emitting diodes employing these polymers as a hole‐transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen‐linked poly(2,7‐carbazole) P3 with p,p′‐biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m‐phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880–3891, 2009     

New blue electroluminescent n‐type polyfluorene copolymers with a 1,3,4‐oxadiazole unit in the main chain

Novel polyfluorene copolymers alternately having an 1,3,4‐oxadiazole unit in the main chain were prepared by both one‐step and two‐step methods for polyoxadiazole synthesis. They displayed highly efficient blue photoluminescence, the properties of which were affected by the extent of conjugation and the changes in the electron density by a side chain. An electrochemical analysis of the polymers using cyclic voltammetry suggested that they could be used as electron‐transport/hole‐blocking materials as well as blue emission materials for polymer light‐emitting diodes. A simple double‐layer device consisting of poly(N‐vinylcarbazole) as a hole‐transport layer and poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐((1,4‐bis(1,3,4‐oxadiazole)‐2,5‐di(2‐ethylhexyloxy)phenylene)‐5,5′‐diyl)] as an emission layer exhibited narrow blue electroluminescence with a maximum at 430 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1058–1068, 2004     

叔丁基联苯基苯基噁二唑作空穴限制层的掺杂聚合物蓝光发光二极管

叔丁基联苯基苯基噁二唑作空穴限制层的掺杂聚合物蓝光发光二极管马於光,吴军,薛善华,黄劲松,田文晶,刘式墉,沈家骢,刘晓冬（吉林大学分子光谱与分子结构开放实验室,集成光电子学国家重点实验室,长春,１３００２３）（白求恩医科大学基础部）关键词聚合物,发光...     

Electroluminescent Properties of an Electrochemically Cross‐Linkable Carbazole Peripheral Poly(Benzyl Ether) Dendrimer

The electroluminescent (EL) properties of a cross‐linkable carbazole‐terminated poly(benzyl ether) dendrimer, G₃‐cbz DN, doped into a PVK:PBD host matrix with a double‐layer device configuration are investigated. Different concentrations of the guest material can control device efficiency, related to chromaticity of white emission and the origin of excited‐state complexes occurring between hole‐transporting carbazole units (PVK or G₃‐cbz DN) and electron‐transporting oxadiazole (PBD). Two excited states (exciplex and electroplex) generated at the interfaces of PVK/G₃‐cbz DN and PBD result in competitive emission, exhibiting a broad band in the EL spectra.     

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     

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 and electrochemical and electroluminescent properties of N‐phenylcarbazole‐substituted poly(p‐phenylenevinylene)

An N‐phenylcarbazole‐containing poly(p‐phenylenevinylene) (PPV), poly[(2‐(4′‐carbazol‐9‐yl‐phenyl)‐5‐octyloxy‐1,4‐phenylenevinylene)‐alt‐(2‐(2′‐ethylhexyloxy)‐5‐methoxy‐1,4‐phenylenevinylene)] (Cz‐PPV), was synthesized, and its optical, electrochemical, and electroluminescent properties were studied. The molecular structures of the key intermediates, the carbazole‐containing boronic ester and the dialdehyde monomer, were crystallographically characterized. The polymer was soluble in common organic solvents and exhibited good thermal stability with a 5% weight loss at temperatures above 420 °C in nitrogen. A cyclic voltammogram showed the oxidation peak potentials of both the pendant carbazole group and the PPV main chain, indicating that the hole‐injection ability of the polymer would be improved by the introduction of the carbazole‐functional group. A single‐layer light‐emitting diode (LED) with a simple configuration of indium tin oxide (ITO)/Cz‐PPV (80 nm)/Ca/Al exhibited a bright yellow emission with a brightness of 1560 cd/m² at a bias of 11 V and a current density of 565 mA/cm². A double‐layer LED device with the configuration of ITO/poly(3,4‐ethylenedioxy‐2,5‐thiophene):poly (styrenesulfonic acid) (60 nm)/Cz‐PPV (80 nm)/Ca/Al gave a low turn‐on voltage at 3 V and a maximum brightness of 6600 cd/m² at a bias of 8 V. The maximum electroluminescent efficiency corresponding to the double‐layer device was 1.15 cd/A, 0.42 lm/W, and 0.5%. The desired electroluminescence results demonstrated that the incorporation of hole‐transporting functional groups into the PPVs was effective for enhancing the electroluminescent performance. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5765–5773, 2005     

Synthesis and tunable emission of novel polyfluorene co-polymers with 1,8-naphthalimide pendant groups and application in a single layer-single component white emitting device

New luminescent polymers containing two individual emission species-poly(fluorene-alt-phenylene) as a blue host and variable amounts of 1,8-naphthalimide as red dopant have been designed and synthesized. Optical studies (optical absorption (OA) and steady-state photoluminescence emission (PL)) in diluted solutions and thin solid films reveal that the emission spectrum can be tuned by varying the content of 1,8-naphthalimide moieties. Although no significant interaction can be observed between both moieties in the ground state, after photoexcitation an efficient energy transfer takes place from the PFP backbone to the red chromophore, indeed, by adjusting the polymer/naphthalimide ratio it is possible to obtain single polymers which emit white light to the human eye in solid state. Energy transfer is more effective in the co-polymers than in physical mixtures of the two chromophores. We prepared single-layer electroluminescent simple devices with structure: ITO/poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS)/active layer/Ba/Al. With this single layer-single component device structure, white light with Commission Internationale de l’Eclairage (CIE) color coordinates (0.3, 0.42) is obtained for the electroluminescence (EL) emission with an efficiency of 22.62 Cd/A.