Synthesis and characterization of a novel fluorene‐alt‐carbazole polymer to host green,blue, and red phosphorescence

A novel fluorene‐alt‐carbazole polymer host Poly(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl‐alt‐N‐tetrahydropyran‐3,6‐carbazole) (PFCz), composed of N‐tetrahydropyran‐3,6‐carbazole and 9,9‐dioctyl‐2,7‐fluorene in the polymer backbone, was synthesized by Suzuki coupling. The PFCz possesses good thermal stability and proper lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) energy levels to facilitate the injection and transport of electrons and holes. Upon doping with blue, green, and red phosphors, red ‐ green ‐ blue (R‐G‐B) phosphorescent devices hosted by PFCz have been fabricated and investigated. In contrast to those of blue and green devices, the red devices give better performances with a maximum luminous efficiency of 4.88 cd/A and a maximum power efficiency of 1.85% at 149.84 cd/m², due to favorable triplet energy level (E_T) of PFCz for red phosphor, bis(2‐methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) [Ir(MDQ)₂(acac)]. Additionally, with different doped concentrations of Ir(MDQ)₂(acac), the PFCz‐related red devices emit nearly pure red light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.57, 0.38), (0.60, 0.38), (0.61, 0.38), and (0.62, 0.38), which were very close to the standard red (0.66, 0.34) by the National Television System Committee. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43234.     

Carbazole/fluorene copolymers with dimesitylboron pendants for blue light-emitting diodes

A series of random and alternating carbazole/fluorene copolymers with various dimesitylboron-containing carbazole derivative contents were synthesized by Suzuki polymerization for use as a light-emitting layer in blue light-emitting diodes. Two carbazole derivatives, CzPhB and CzPhThB consisted of a carbazoyl group as the donor and a dimesitylboron group as the acceptor group, separated by phenyl and phenyl-thiophene groups π-conjugated systems, respectively. The copolymers exhibited good thermal stability and blue emission in both solution and the solid state. Moreover, the CzPhB/fluorene and CzPhThB/fluorene copolymers exhibited a higher PL quantum efficiency than the fluorene-based homopolymer (POF). Higher brightness and larger current efficiency were observed for the CzPhB/fluorene and CzPhThB/fluorene copolymer-based devices compared to the POF-based device. Additionally, the CzPhThB/fluorene copolymer-based devices had better EL performances than the CzPhB/fluorene copolymer-based devices. The turn-on voltage, maximal brightness, and highest luminescence efficiency of the carbazole/fluorene copolymer-based devices were found to be 4.5-8.5 V, 436 cd/m², and 0.51 cd/A, respectively.     

Synthesis and electrophosphorescent device study of carbazole containing dendronized styrenic polymers

Styrenic polymers P1(G0-CZ) and P2(G2-CZ) with carbazoles and carbazole containing dendrons as side chains were efficiently synthesized via “graft-to” approach by using copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The new polymers showed wide band gaps and had good thermal stabilities. Two new polymers were studied as electrophosphorescent host materials in OLED devices. Electrophosphorescent devices with the configuration of ITO/PEDOT:PSS/polymers:Ir(ppy)₃/TPBI/LiF/Al were fabricated. The polymer P1(G0-CZ) based device showed a maximum current efficiency of 21.4 cd/A, a power efficiency of 12.7 lm/W and an external quantum efficiency of 6.02%. The effect of host polymer structures on the aggregation of transition metal complexes Ir(ppy)₃ in active layer was also investigated.     

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

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

Synthesis and light emitting properties of sulfide-containing polyfluorenes and their nanocomposites with CdSe nanocrystals: A simple process to suppress keto-defect

A new series of sulfide-containing polyfluorene homopolymers and copolymers (PFS, PF1, PF3 and PF4) comprising 9,9-di[11-(decylsulfanyl)undecyl] fluorene, 9,9-dihexylfluorene, triphenylamine or benzothiadiazole moieties were synthesized by Ni(0)-mediated Yamamoto-coupling and palladium-catalyzed Suzuki polymerizations. Three other polyfluorenes (PF2, PF5 and PFC6) without sulfur atom in the alkyl side chains were also synthesized by a similar method for comparison purpose. These fluorene-based polymers were characterized using FT-IR spectroscopy, elemental analysis, DSC, TGA, photoluminescence (PL) and electroluminescence (EL) spectroscopies. The synthesized polymers PFS and PF1–PF3 emit blue light at around 440–468 nm, while copolymers PF4 and PF5 emit green light at around 540 nm. In annealing experiments, these polymer films show better stability against thermal oxidation than polymer PFC6. Sulfide-containing polymers show not only good electroluminescent color stability, but their EL spectra also remain unchanged at high driving voltage. A multi-layer electroluminescent device with the configuration of ITO/PEDOT/PF1/CsF/Al exhibited a stable sky-blue emission with color coordinates (0.21, 0.23) at 10 V, which showed a maximum brightness of 2991 cd/m² at 8 V (75 mA/cm²) and a maximum efficiency of 1.36 cd/A. Finally, by ligand exchange process, the sulfur element could form coordination bonding with quantum dots, and PLED devices using these new QDs-containing organic/inorganic hybrid materials as light-emitting layers exhibit superior or comparable EL performance compared to those without quantum dots.     

Synthesis and characterization of poly(fluorene vinylene) copolymers containing thienylene–vinylene units

Narrow‐band‐gap 2,5‐thienylene‐divinylene (ThV) units were incorporated into the poly(fluorene vinylene) backbone via a Gilch reaction as an energy trap with various feed ratios; this yielded pronounced changes in the electrochemical and optical properties of the material. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the polymers {poly(9,9‐di‐iso‐octylfluorene vinylene) [poly(fluorene vinylene‐co‐thiophene vinylene (FV))], C1, and C2 } were estimated to be ?5.53 to ?5.10 eV and ?2.98 to ?2.84 eV, respectively, by cyclic voltammetry measurements. In comparison with poly(FV), the HOMO energy levels of polymers poly(fluorene vinylene‐co‐thiophene vinylene (FV) (90 : 10) ( C1 ) and poly(fluorene vinylene‐co‐thiophene vinylene (FV) (80 : 20) ( C2 ) were significantly increased, but their LUMO energy levels were slightly decreased. The optical properties were investigated by absorption and emission spectra of the polymers. The good spectral overlap between the emission of poly(FV) and the absorption of polymers C1 and C2 revealed a sufficient energy transfer from the majority of 9,9‐di‐iso‐octylfluorene vinylene units to the minority of ThV units. The reduction of self‐absorption losses of polymers C1 and C2 due to spectral separation caused by the incorporation of ThV units could be indirectly confirmed by nonlinear optical (NLO) properties. The result of the NLO properties of the polymers showed that the third‐order NLO coefficients of poly(FV), C1, and C2 were 8.1 × 10^?10, 1.35 × 10^?9, and 1.51 × 10^?9 esu, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and performances of 9,9-bis(perfluorohexylethyl propionate) fluorene copolymers

2,7-dibromo-9,9-bis(perfluorohexylethyl propionate) fluorene was synthesized by Michael addition reaction using 2,7-dibromofluorene and perfluorohexyl ethyl acrylate as the reactants. 9,9-Bis(perfluorohexylethyl propionate) fluorene copolymers were then synthesized by Suzuki coupling reaction with 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborane-diyl)-9,9 -dioctyl fluorene, 2,7-dibromo-9,9-dioctyl fluorene and 2,7-dibromo-9,9-bis(perfluorohexylethyl propionate) fluorene as the monomers. The fluorinated fluorene copolymers were characterized and investigated via Fourier infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance spectroscopy (¹HNMR), ultraviolet absorption spectroscopy (UV–vis), cyclic voltammetry (CV) and photoluminance spectroscopy (PL). Because of the long fluorine-containing alkyl side chain, the ultraviolet absorption peak of 9,9-bis(perfluorohexylethyl propionate) fluorene is blue-shifted compared with poly(9,9-dioctylfluorene)(PF8). The LUMO energy level increases and the energy band gap of copolymers widens. Due to the self-assembly of the long fluoroalkyl side chain, the photoluminance spectra of 9,9-bis(perfluorohexylethyl propionate) fluorene copolymers exhibit a new excimer emission peak at 550 nm. The photoluminance stabilities of the copolymers under irradiation and humid conditions are significantly improved due to protective effect from the long fluoroalkyl side chain. After being irradiated under 500 W iodine tungsten lamp or kept under 70% relative humid conditions, the 9,9-bis(perfluorohexylethyl propionate) fluorene copolymers showed much better photoluminance stability than that of poly(9,9-dioctylfluorene) (PF8). These show that introducing long fluoroalkyl side chain into conjugated polymer main chain is a promising strategy to improve environmental stability of devices based on organic conjugated polymers.     

Synthesis,characterization, and optoelectronic properties of two new polyfluorenes/poly(p‐phenylenevinylene)s copolymers

Two novel copolymers of polyfluorenes/poly(p‐phenylenevinylene)s copolymers with p‐tert‐butyl‐phenylenemethylene groups in the C‐9 position of alternating fluorene unit, poly[1,4‐(2,5‐dibutyloxyl)‐phenyleneviny lene‐alt‐9‐(p‐tert‐butyl‐phenylenemethylene)fluorene] and poly[1,4‐(2,5‐dioctyloxyl)‐phenylenevinylene‐alt‐9‐(p‐tert‐butyl‐phenylenemethylene)fluorine], have been synthesized via the Heck polycondensation reaction. The synthesized polymers were characterized by FTIR, NMR, DSC, TGA, UV–vis, and PL spectra. The polymers showed high glass transition temperatures and good thermal stability. A polymer light‐emitting diode with the configuration ITO/PEDOT:PSS/P2/Ca/Al has been fabricated. The device emitted a yellow light with a peak wavelength of 578 nm similar to the PL spectra of the copolymer film. A maximal luminance of 534 cd/m² was obtained at a driving voltage of 24.5 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3955–3962, 2006     

Synthesis and characterization of fluorene end-labeled polymers prepared by nitroxide-mediated polymerization

The fluorene-based alkoxyamine 9-(2,2,6,6-tetramethyl-4-hydroxypiperidinyloxy)fluorene was prepared and investigated as a unimolecular initiator in the nitroxide-mediated polymerization (NMP) of styrene. Reactions performed in either bulk or ethereal solvents at 125 °C generated polymers possessing low polydispersity indices (PDIs) and number average molecular weight (M_n) values close to those anticipated based on monomer-to-initiator ratios. A linear relationship between monomer conversion and M_n values was observed by analysis of reaction aliquots with ¹H NMR and gel permeation chromatography (GPC), while PDI values remained low throughout. Analysis of the polymers by UV–vis spectroscopy indicated that approximately 80% of the polymer chains were labeled with the fluorene chromophore, while fluorescence spectroscopy was used to verify that the fluorene was polymer-bound.     

Synthesis of Benzothiadiazole-Based Liquid Crystalline Polyacrylates for Polarized Light Emitting Diodes

Two benzothiadiazole-based liquid crystalline polyacrylates were synthesized. These polymers revealed a nematic liquid crystal phase and exhibited photoluminescence as well as polarized electroluminescence when incorporated into light-emitting diode applications. The polymers showed dichroic ratios of about 8.3–8.8 in UV-vis absorption and photoluminescence emission. The polymer with vinylene linkages (P2) showed better electroluminescence device performance than that with acetylene linkages (P1). The P2 device emitted red light at 604 nm with a turn-on voltage at 6 V, and a maximum polarized luminance of 235 cd/m² at 12 V, with an efficiency of 0.09 cd/A and a polarization ratio of 6.5.     

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

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

White Electroluminescence from a Single-Polymer System with Simultaneous Three-color Emission

A series of polymers were synthesized by incorporating low contents of fluorenone (FO) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) into the main chain of poly(9,9-dioctylfluorene). White-light emission was obtained from a single polymer by adjusting the FO and DBT contents. All polymers showed good thermal stability with 5% weight loss up to 410 °C and good solubility in common organic solvents. Electroluminescence devices with indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/emission layer/Ca/Al structure were found to emit white light with Commission Internationale de l’Eclairage coordinate of (0.37, 0.34). These devices exhibited a maxium brightness of 3414 cd/m² and a maximum current efficiency of 2.79 cd/A.     

Electroluminescent Characteristics of DBPPV–ZnO Nanocomposite Polymer Light Emitting Devices

We have demonstrated that fabrication and characterization of nanocomposite polymer light emitting devices with metal Zinc Oxide (ZnO) nanoparticles and 2,3-dibutoxy-1,4-poly(phenylenevinylene) (DBPPV). The current and luminance characteristics of devices with ZnO nanoparticles are much better than those of device with pure DBPPV. Optimized maximum luminance efficiencies of DBPPV–ZnO (3:1 wt%) before annealing (1.78 cd/A) and after annealing (2.45 cd/A) having a brightness 643 and 776 cd/m² at a current density of 36.16 and 31.67 mA/cm² are observed, respectively. Current density–voltage and brightness–voltage characteristics indicate that addition of ZnO nanoparticles can facilitate electrical injection and charge transport. The thermal annealing is thought to result in the formation of an interfacial layer between emissive polymer film and cathode.     

Synthesis and characterization of novel poly(arylenevinylene) derivative

The new poly(arylenevinylene) derivative composed naphthalene phenylene vinylene backbone was developed. The theoretical calculation showed that the model compound of the obtained polymer was highly distorted between the stryl and naphthalene units as well as between the backbone and fluorene side units. The polymer was synthesized by the palladium catalyzed Suzuki coupling reaction with 2,6‐(1′,2′‐ethylborate)‐1,5‐dihexyloxynaphtalene and 1,2‐bis(4′‐bromophenyl)‐1‐(9″,9″‐dihexyl‐3‐fluorenyl)ethene. The structure of the polymer was confirmed by ¹H NMR, IR, and elemental analysis. The weight–average molecular weight of the polymer is 29,800 with the polydispersity index of 1.87. The new polymer showed good thermal stability with high T_g of 195°C. The bright blue fluorescence (λ_max = 475 nm) was observed both in solution and film of new polymer with naphthalene phenylene vinylene backbone. Double layer LED devices with the configuration of ITO/PEDOT/polymer/LiF/Ca/Al showed a turn‐on voltage at around 4.5 V, the maximum luminance of 150 cd/m², and the maximum efficiency of 0.1 cd/A. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Blue‐light‐emitting poly(arylene ethynylenes) containing alternating sequences of biphenylene or fluorenediyl and p‐phenylene moieties linked through triple bonds

Two new poly(arylene ethynylenes) were synthesized by the reaction of 1,4‐diethynyl‐2.5‐dioctylbenzene either with 4,4′‐diiodo‐3,3′‐dimethyl‐1,1′‐biphenyl or 2,7‐diiodo‐9,9‐dioctylfluorene via the Sonogashira reaction, and their photoluminescence (PL) and electroluminescence (EL) properties were studied. The new poly(arylene ethynylenes) were poly[(3,3′‐dimethyl‐1,1′‐biphenyl‐4,4′‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEBE) and poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEFE), both of which were blue‐light emitters. PPEBE not only emitted better blue light than PPEFE, but it also performed better in EL than the latter when the light‐emitting diode devices were constructed with the configuration indium–tin oxide/poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (50 nm)/polymer (80 nm)/Ca:Al. The device constructed with PPEBE exhibited an external quantum efficiency of 0.29 cd/A and a maximum brightness of about 560 cd/m², with its EL spectrum showing emitting light maxima at λ = 445 and 472 nm. The device with PPEFE exhibited an efficiency of 0.10 cd/A and a maximum brightness of about 270 cd/m², with its EL spectrum showing an emitting light maximum at λ = 473 nm. Hole mobility (μ_h) and electron mobility (μ_e) of the polymers were determined by the time‐of‐flight method. Both polymers showed faster μ_h values. PPEBE revealed a μ_h of 2.0 × 10^?4 cm²/V·s at an electric field of 1.9 × 10⁵ V/cm and a μ_e of 7.0 × 10^?5 cm²/V·s at an electric field of 1.9 × 10⁵ V/cm. In contrast, the mobilities of the both carriers were slower for PPEFE, and its μ_h (8.0 × 10^?6 cm²/V·s at an electric field of 1.7 × 10⁶ V/cm) was 120 times its μ_e (6.5 × 10^?8 cm²/V·s at an electric field of 8.6 × 10⁵ V/cm). The much better balance in the carriers' mobilities appeared to be the major reason for the better device performance of PPEBE than PPEFE. Their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels were also a little different from each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 299–306, 2006     

Carbon nanotube modified electrodes for enhanced brightness in organic light emitting devices

Acid oxidised multiwall carbon nanotubes (COOH-MWCNT) have been introduced as a hole injection buffer layer in an organic light emitting diodes (OLED). We show that the OLED with COOH-MWCNT as a buffer layer provides higher brightness with lower operating voltages. The addition of a COOH-MWCNT buffer layer has enabled a further increase in the brightness of our OLED devices operating in excess of 20,000 cd/m² due to enhanced hole injection by several orders of magnitude. The increase in current injection and brightness does not alter the optical emission spectrum at different operating voltages in these devices. A model is proposed to explain this increase in current injection and brightness based on the modified electron energy band alignment.     

Synthesis and optoelectronic properties of luminescent copolyfluorenes slightly doped with thiophene chromophore

This paper describes the synthesis of new copolyfluorenes (P05-P5) slightly doped with 2,5-bis(2-phenyl-2-cyanovinyl)thiophene (GM, <3.4 mol%) and their application in electroluminescent (EL) devices. In film state, EL spectra of the copolyfluorenes are very different from photoluminescence (PL) spectra, which have been ascribed to charge trapping in GM and energy transfer from fluorene segments to GM chromophores. The maximum brightness and current efficiency of EL device from P05 (5230 cd/m², 0.65 cd/A) are significantly enhanced when compared with those from poly(9,9-dihexylfluorene) (PF) (1310 cd/m², 0.18 cd/A). The EL device using blend of P5 and PF (w/w = 10/1) as emitting layer exhibits near-white emission with CIE coordinate being (0.26, 0.32). The results demonstrate that the copolyfluorenes slightly doped with GM chromophore are promising emitting materials for optoelectronic devices.     

Novel green light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide-arylamine derivatives

Green light-emitting polyfluorenes were synthesized by Suzuki polycondensation via introducing dibenzothiophene-S,S-dioxide-(di-)tri-phenylamine (G₁ and G₂) moieties and dibenzothiophene-S,S-dioxide (SO) unit into the polyfluorene backbone, respectively. PF–SO–G copolymers show a high thermal stability and a moderate photoluminescence quantum yield in the range of 20–40%. The lowest unoccupied molecular orbital (LUMO) levels reduce with increasing the content of SO unit in the polymers. The efficient energy transfer from fluorene segment to G₁ or G₂ unit occurred in the PL process, and the EL emission peaked at about 510 nm was exclusively from G₁ or G₂ unit. Incorporating SO unit into the polymer backbone makes the device performances improved. The maximal luminous efficiency of 9.0 cd A^?1 with the CIE coordinates of (0.27, 0.56) was obtained for PF–SO15-G₂5 based on a single-layered device of ITO/PEDOT:PSS/polymer/CsF/Al. And the polymers (PF–SO15-G5)s exhibited a dramatic LE stability at high current densities, even though at the current density of 200 mA cm^?2, the luminous efficiencies only dropped 10%. SO unit lowers the LUMO level, balances the injection and transportation of both electron and hole in the polymers, and therefore improves the device performances. The hole- and electron-only devices show that the hole and electron flux are well balanced, which demonstrates that (PF-SO15-G5)s are bipolar polymers with a balanced charge carrier transport.     

Polylactide‐perylene derivative for blue biodegradable organic light‐emitting diodes

In this work we demonstrate, for the first time, the use of polylactic acid (PLA) as a biodegradable host matrix for the construction of the active emissive layer of organic light‐emitting diode (OLED) devices for potential use in bioelectronics. In this preliminary study, we report a robust synthesis of two fluorescent PLA derivatives, pyrene‐PLA ( AH10 ) and perylene‐PLA ( AH11 ). These materials were prepared by the ring opening polymerisation of l ‐lactide with hydroxyalkyl‐pyrene and hydroxyalkyl‐perylene derivatives using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as catalyst. OLEDs were fabricated from these materials using a simple device architecture involving a solution‐processed single‐emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD‐7 (35%): AH10 or AH11 (20%)/TPBi/LiF/Al (ITO, indium tin oxide; PEDOT:PSS, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid); PVK, poly(vinylcarbazole); OXD‐7, (1,3‐phenylene)‐bis‐[5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole]; TPBi, 2,2′,2″‐(1,3,5‐benzenetriyl)tris(1‐phenyl‐1H‐benzimidazole)). The turn‐on voltage for the perylene OLED at 10 cd m^–2 was around 6 V with a maximum brightness of 1200 cd m^–2 at 13 V. The corresponding external quantum efficiency and device current efficiency were 1.5% and 2.8 cd A^–1 respectively. In summary, this study provides proof of principle that OLEDs can be constructed from PLA, a readily available and renewable bio‐source. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

Synthesis of laterally attached side-chain liquid crystalline poly(p-phenylene vinylene) and polyfluorene derivatives for the application of polarized electroluminescence

Two series of poly(p-phenylene vinylene) and polyfluorene derivatives (PPV1-PPV4 and PF1-PF5) containing laterally attached penta(p-phenylene) mesogenes were synthesized and characterized. These polymers show nematic liquid crystalline behavior. The optical properties of the polymers were investigated by UV-vis absorption and photoluminescence spectrometers and these polymers were fabricated to form the polarized electroluminescent devices using poly(ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS) as an alignment layer. In the series of poly(p-phenylene vinylene) derivatives, polymer PPV4 offered the best EL device performance. It emitted yellow light at 588 nm at 4 V. The maximum brightness was about 1337 cd/m² at 9 V with a polarized ratio of 2.6. In another series of polyfluorene derivatives, PF4 offered the best EL device performance with the polarized ratio of 12.4 and a maximum luminescence of 1855 cd/m². In the case of polarized white light, as a consequence of blending small amount of PF4 and PF5 with a host polymer PF2, polarized ratio of up to 10.2 and a maximum brightness of 2454 cd/m² have been attained. The aligned films exhibited pronounced polarized ratio, implying that the polymers exhibit potential for linearly polarized LED application.