Synthesis,characterization, and electroluminescence of fluorene and carbazole‐based blue light‐emitting polymers with different noncoplanar molecular architectures

In order to investigate the explicit optoelectronic variations of the photoluminescent polymer with sterically hindered side chains, three novel alternate polymers (P0, P1, and P2) based on fluorene and carbazole moieties were successfully synthesized through Suzuki coupling reaction. The molecular structures of the polymers were fully characterized by ¹H‐NMR, ¹³C‐NMR, elemental analysis, and gel permeation chromatograph, respectively. The photophysical properties, thermal stability, and energy band gaps of polymers P0, P1, and P2 were further examined through UV–vis absorption, photoluminescent spectra, differential scanning calorimetry, thermogravimetric analysis, and cyclic voltammetry. The experimental results indicated that the polymers took on wide band gaps of about 3.50 eV with deep blue emission in thin solid films. These polymers were found to show a high thermal stability with decomposition temperatures at 5% weight loss of the compounds in the range of 353–416 °C. Blue light‐emitting electroluminescent devices of the most branched polymer P2 with highest light‐emitting efficiency as emitting layers were characterized, which showed obviously improved spectral stabilities with respect to the parent polyfluorene materials. In conclusion, we have established an effective method to improve the spectral stabilities of polyfluorene material by synthesizing the zigzag‐shaped copolymer of fluorene and carbazole with sterically hindered pendant moieties of different molecular sizes. Copyright © 2014 John Wiley & Sons, Ltd.     

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

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

Enhanced efficiency of polyfluorene derivatives: Organic–inorganic hybrid polymer light‐emitting diodes

Two novel organic–inorganic hybrid polyfluorene derivatives, poly{(9,9′‐dioctyl‐2,7‐fluorene)‐co‐(9,9′‐di‐POSS‐2,7‐fluorene)‐co‐[2,5‐bis(octyloxy)‐1,4‐phenylene]} (PFDOPPOSS) and poly{(9,9′‐dioctyl‐2,7‐fluorene)‐co‐(9,9′‐di‐POSS‐2,7‐fluorene)‐co‐bithiophene} (PFT2POSS), were synthesized by the Pd‐catalyzed Suzuki reaction of polyhedral oligomeric silsesquioxane (POSS) appended fluorene, dioctyl phenylene, and bithiophene moieties. The synthesized polymers were characterized with ¹H NMR spectroscopy and elemental analysis. Photoluminescence (PL) studies showed that the incorporation of the POSS pendant into the polyfluorene derivatives significantly enhanced the fluorescence quantum yields of the polymer films, likely via a reduction in the degree of interchain interaction as well as keto formation. Additionally, the blue‐light‐emitting polyfluorene derivative PFDOPPOSS showed high thermal color stability in PL. Moreover, single‐layer light‐emitting diode devices of an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration fabricated with PFDOPPOSS and PFT2POSS showed much improved brightness, maximum luminescence intensity, and quantum efficiency in comparison with devices fabricated with the corresponding pristine polymers PFDOP and PFT2. In particular, the maximum external quantum efficiency of PFT2POSS was 0.13%, which was twice that of PFT2 (0.06%), and the maximum current efficiency of PFT2POSS was 0.38 cd/A, which again was twice that of PFT2 (0.19 cd/A). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2943–2954, 2006     

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

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

Highly efficient and stable blue‐light‐emitting binaphthol‐fluorene copolymers: A joint experimental and theoretical study of the main‐chain chirality

In a quest for the main‐chain chiral and highly stable blue‐light‐emitting π‐conjugated polymers, a novel series of soluble conjugated random and alternating copolymers (PF‐BN) derived from fluorene and axially chiral 1,1′‐binaphthol (BINOL) were successfully synthesized by Suzuki coupling polymerization. The polymer structures, optical properties, and their electrochemical properties were investigated by ¹H NMR, TGA/DSC, UV‐Vis absorption, photoluminescence, cyclic voltammetry, circular dichroism spectroscopy, and DFT calculations. The blue‐light‐emitting BINOL‐containing copolymers with proper content of BINOL show highly efficient photoluminescence and ultra highly stable light‐emission with almost unchanged fluorescent spectra after annealing at 200 °C in air for 10 h. The joint experimental and theoretical study of the main‐chain chirality reveals that (1) the chirality of BINOL can be transferred to the polymer backbone, (2) the effective conjugation length is about one BINOL and three fluorenes, (3) the main active chiral block in the copolymers is probably composed by one BINOL with the other two or three fluorenes, and (4) the dihedral angle in the PF‐BN copolymers should be larger than 105°. The incorporation of BINOL into the polyfluorene backbone is an effective way to produce highly efficient and stable blue‐light‐emitting main‐chain chiral conjugated polymer with interesting optoelectronic properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3868–3879, 2010     

Highly efficient and stable blue‐light‐emitting copolyfluorene consisting of carbazole,oxadiazole, and charge‐trapping anthracene groups

This article presents the synthesis and electroluminescent (EL) properties of a stable blue‐light‐emitting copolyfluorene ( P1 ) consisting of carbazole, oxadiazole and charge‐trapping anthracene groups by Suzuki coupling reaction. The hole‐transporting carbazole and electron‐transporting oxadiazole improve charges injection and transporting properties, whereas the anthracene is the ultimate emitting chromophore. The thermal, photophysical, electrochemical, and EL properties of P1 were investigated by thermogravimetric analysis, differential scanning calorimeter, optical spectroscopy, cyclic voltammetry, and EL devices fabrication and characterization. P1 demonstrated high‐thermal stability with thermal decomposition and glass tranistion temperatures above 400 and 145°C, respectively. In film state, P1 showed blue emission at 451 nm attributed to anthracene chromophore. Photophysical and electrochemical investigations demonstrate that effective energy transfer from fluorene to anthracene segments and charges trapping on anthracene segments leads to efficient and stable blue emission originating from anthracence. Polymer light‐emitting diodes using P1 as the emitting layer (ITO/PEDOT:PSS/ P1 /Ca/Al) exhibited excellent current efficiency (5.1 cd/A) with the CIE coordinate being (0.16, 0.11). The results indicate that copolyfluorene is a promising candidate for the blue‐emitting layer in the fabrication of efficient PLEDs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Design,synthesis, photophysical,and electrochemical properties of DCM‐based conjugated polymers for light‐emitting devices

A series of conjugated hyperbranched polymers, hyperbranched copolymers, and linear polymers containing 2‐pyran‐4‐ylidenemalononitrile (acceptor) and triphenylamine/fluorene (donor) units were synthesized and characterized by FTIR, ¹H NMR, thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, UV–visible, photoluminescence, and cyclic voltammetry measurements. All the polymers show red‐light emission in the range of 566–656 nm both in solution and in solid state. The quantum efficiency of the polymers was in the range of 56–82%. Among the six polymers synthesized, only polymers containing fluorene units show T_g and polymers based on triphenylamine not exhibit T_g. The band gap of these polymers were found to be reasonably low; hyperbranched copolymer containing fluorene unit shows lowest band gap of 2.18 eV due to the stabilization of LUMO energy level by the electron withdrawing ? CN groups. The thermal and solubility behavior of the polymers were found to be good. All the EL spectra of the devices (indium‐tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/polymer/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline/tris(8‐hydroxyquinoline)aluminum)/LiF/Al) show red‐light emission, and the device fabricated with P3 and P4 shows maximum luminance and luminous efficiency of 4104 cd m^?2 and 0.55 cd Å^?1 and 3696 cd m^?2 and 0.47 cd Å^?1, respectively, indicates that they had the best carrier balance. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polyfluorene derivatives pending iridium complexes: Improved optoelectronic properties by introducing D‐A units and altering pendent mode

To study influence of the donor(D)‐acceptor(A) units and pendent mode of phosphorescent moiety on the opto‐electronic properties for its resulting copolymers, two D‐A‐based polyfluorene derivatives ( P 1 and P 2) pending the red‐emitting iridium bi(phenylisoquilonato) (picolinato) [Ir(Piq)₂(pic)] unit and a polyfluorene derivative ( P 3) only pending Ir(Piq)₂(pic) unit were synthesized and characterized, in which the donor of carbazole, the acceptor of oxadiazole are grafted into the C‐9 position of fluorene, the Ir(Piq)₂(pic) unit is pended into either the C‐9 position for P 1 and P 3 or the end for P 2 of fluorene by unconjugated linkage, respectively. Their opto‐electronic properties were significantly influenced by the D‐A units and pendent mode of the Ir(Piq)₂(pic) unit. In the polymer light‐emitting devices with a configuration of ITO/PEDOT/polymers/LiF/Al, the P 1 showed best electroluminescent properties than the P 2 and P 3. The maximum current efficiency of 0.72 cd/A and the highest luminance of 1398 cd/m 2 were obtained in the P 1‐based device, which are 1.3 and 1.5 times higher than those in the P 2‐based device, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of nitrogen‐linked carbazole‐containing fluorescent polymers

We have prepared four light‐emitting polymers bearing a chromophore composed of carbazole and fluorene by the Suzuki coupling polycondensation. Two nonconjugated polymers (P3CzBFXy and P2CzFXy) had a chromophore tethered by the p‐xylylene spacer, whose connection point between carbazole and fluorene in addition to the number of fluorene unit was systematically changed to investigate the emission wavelength and intensity. The red‐shifted absorption and emission maximum wavelengths together with the improved fluorescence quantum yield of polymers P3CzBFXy and P2CzFXy indicate that the increment of the number of para‐connected benzene rings included in the chromophore effectively extends the conjugation length. The fact that polymer P3CzBFXy has longer wavelength absorption and emission spectra also indicates the interaction of the carbazole nitrogen lone pair with the oligophenylene moiety. Other two polymers P3CzFPy and P3CzFPym having the heterocycle directly bound to the carbazole nitrogen were prepared to know the character of the carbazole nitrogen lone pair and their influence on the fluorescence behavior. The fluorescence spectra of polymer P3CzFPym bearing the pyrimidine ring gradually red‐shifted in conjunction with the decrease of fluorescence quantum yield on going from toluene solution to CHCl₃ solution because of the intramolecular charge transfer at the excited state. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3729–3735, 2010     

Blue light‐emitting hyperbranched polymers using fluorene‐co‐dibenzothiophene‐S,S‐dioxide as branches

A series of blue light‐emitting hyperbranched polymers comprising poly(fluorene‐co‐dibenzothiophene‐S,S‐dioxide) as the branch and benzene, triphenylamine, or triphenyltriazine as the core were synthesized by an “A₂ + A₂' + B₃” approach of Suzuki polymerization, respectively. All resulted copolymers exhibited quite comparable thermal properties with the glass transition temperatures in the range of 59–68 °C and relatively high decomposition temperatures over 420 °C. Photoluminescent spectra exhibited slight variation with the molar ratio of the dibenzothiophene‐S,S‐dioxide unit and the size of the core units. Polymer light‐emitting devices demonstrated blue emission with excellent stability of electroluminescence. Copolymers based on smaller core units of benzene and triphenylamine exhibited enhanced device performances regarding to that of triphenyltriazine. With the device configuration of ITO/PEDOT:PSS/polymer/CsF/Al, a maximum luminous efficiency of 4.5 cd A^?1 was obtained with Commission Internationale de L'.Eclairage (CIE) coordinates of (0.16, 0.19) for the copolymer PFSO15B. These results indicated that hyperbranched structure can be a promising strategy to attain spectrally stable blue‐light‐emitting polymers with high efficiency. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1043–1051     

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     

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     

Triarylamine N‐functionalized 3,6‐linked carbazole main chain polymers and copolymers: Preparation and physical properties

The preparation of triarylamine N‐functionalized 3,6‐linked carbazole homopolymers as well as alternating copolymers with 2,5‐diphenyl‐[1,3,4]oxadiazole and benzo[1,2,5]thiadiazole was undertaken using Suzuki cross‐coupling polymerization procedures associating 3,6‐bis(4,4,5,5‐tetramethyl‐[1,3,2]dioxaborolan‐2‐yl)‐9‐(bis[4‐(2‐butyl‐octyloxy)‐phenyl]‐amino‐phen‐4‐yl)‐carbazole and, respectively, 3,6‐dibromo‐9‐(bis[4‐(2‐butyl‐octyloxy)‐phenyl]‐amino‐phen‐4‐yl)‐carbazole, 2,5‐bis(4‐bromo‐phenyl)‐[1, 3,4]oxadiazole, and 4,7‐dibromo‐benzo[1,2,5]thiadiazole. Both the carbazole homopolymer and alternating copolymer with 2,5‐diphenyl‐[1,3,4]oxadiazole were found as wideband gap materials emitting in the blue part of the electromagnetic spectrum while the carbazole alternating copolymer with 4,7‐benzo[1,2,5]thiadiazole had a narrower band gap and emitted in the orange part of the electromagnetic spectrum. The new polymers are thermally stable up to 300 °C. A discussion of the electrochemical and optical properties of the new polymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5957–5967, 2007.     

Synthesis and characterization of a polyfluorene containing carbazole and oxadiazole dipolar pendent groups and its application to electroluminescent devices

We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007     

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

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

Poly[2,7‐(9,9‐dihexylfluorene)‐alt‐pyridine] with donor‐acceptor architectures: A new series of blue‐light‐emitting alternating copolymers

A novel series of well‐defined alternating poly[2,7‐(9,9‐dihexylfluorenyl)‐alt‐pyridinyl] (PDHFP) with donor‐acceptor repeat units were synthesized using palladium (0)‐catalyzed Suzuki cross‐coupling reactions in good to high yields. In this series of alternating polymers, 2, 7‐(9,9‐dihexylfluorenyl) was used as the light emitting unit, and the electron deficient pyridinyl unit was employed to provide improved electron transportation. These polymers were characterized by ¹H‐NMR and ¹³C‐NMR, gel permeation chromatography (GPC), thermal analyses, and UV‐vis and fluorescence spectroscopy. The glass transition temperature of copolymers in nitrogen ranged from 110 to 148 °C, and the copolymers showed high thermal stabilities with high decomposition temperatures in the range of 350 to 390 °C in air. The difference in linkage position of pyridinyl unit in the polymer backbone has significant effects on the electronic and optical properties of polymers in solution and in film phases. Meta‐linkage (3,5‐ and 2,6‐linkage) of pyridinyl units in the polymer backbone is more favorable to polymer for pure blue emission and prevention of aggregation of polymer chain than para‐linkage (2,5‐linkage) of the pyridinyl units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4792–4801, 2004     

Synthesis and properties of photoluminescent polymers bearing electron‐facilitating oxadiazole derivative side groups

Poly(p‐divinylene phenylene) derivatives bearing fluorene and carbazole units in the main chain and 5‐phenyl‐1,3,4‐oxadiazole moieties as side groups were prepared by the polycondensation of a newly synthesized monomer, [2‐(5′‐phenyl‐1′,3′,4′‐oxadiazole‐2′‐yl)‐1,4‐xylylene]bis(triphenyl phosphonium bromide) (OXAD), with 9,9‐dibutylfluorene‐2,2′‐dicarbaldehyde (DBFDA) and 9‐(2‐ethylhexyl)carbazole‐3,6‐dicarbaldehyde (EHCDA), which gave DBFDA–OXAD and EHCDA–OXAD. Analogues of these polymers without the side groups were also synthesized by the reaction of 1,4‐xylene bis(triphenyl phosphonium bromide) (PXYL) with the dicarbaldehydes, which gave DBFDA–PXYL and EHCDA–PXYL. All the synthesized polymers are soluble in organic solvents, giving films of good quality. The polymers are stable beyond 375 °C. They emit blue and blue‐green light, and their quantum yields are 38–79% in solution and 1–24% in film, depending on the fluorene and carbazole units as well as the side groups. In particular, the OXAD‐based polymers contain hole‐facilitating backbones and electron‐facilitating side groups, perhaps allowing these polymers to transport both holes and electrons. Overall, the synthesized polymers are potential candidates for the fabrication of light‐emitting devices. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1173–1183, 2002     

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     

White electroluminescent single‐polymer achieved by incorporating three polyfluorene blue arms into a star‐shaped orange core

A series of star‐like dopant/host single‐polymer systems with a D‐A type star‐shaped orange core and three blue polyfluorene arms were designed and synthesized. Through tuning the doping concentration of the orange core and thermal annealing treatment of white polymer light‐emitting diodes based on them, highly efficient white electroluminescence has been achieved. A typical single‐layer device (ITO/PEDOT:PSS/polymer/Ca/Al) realized pure white emission with a luminous efficiency of 16.62 cd A^?1, an external quantum efficiency of 6.28% and CIE coordinates of (0.33, 0.36) for S‐WP‐002TPB3 containing 0.02 mol % orange core. The high efficiency of the devices could be mainly attributed to the suppressed concentration quenching of the dopant units, more efficient energy transfer from polymer host to orange dopant and thermal annealing‐induced α‐phase polyfluorene (PF) self‐dopant in amorphous PF host. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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