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     

Synthesis and characterization of highly stable blue‐light‐emitting hyperbranched conjugated polymers

Polyfluorene homopolymer ( P1 ) and its carbazole derivatives ( P2 – P4 ) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, ¹H NMR, ¹³C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer ( P1 ). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008     

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,characterization, and application of light‐emitting copolyfluorenes slightly doped with distyrylbenzene derivatives

Copolyfluorenes PFG1～PFG4 slightly doped with 0.006–0.5 mol % of 2,5‐dihexyloxy‐1,4‐bis(2‐phenyl‐2‐cyanovinyl)benzene (green chromophore) were synthesized by the Suzuki coupling reaction to be evaluated as hosts for white‐light electroluminescent (EL) devices. Their optical, thermal and electrochemical properties were almost identical to those of polyfluorene ( PF ) due to minimal chromophore content. However, the electroluminescent (EL) spectra of the PFGn were very different from photoluminescence spectra in film state. Relative intensity of green emission (ca. 521 nm) in EL spectra are much stronger than those in PL spectra, which can be attributed to charges trapping in the chromophores due to its narrow band gap (E_g ≈ 2.56 eV). The performance of EL devices [ITO/PEDOT:PSS/polymer/Ca (50 nm)/Al (100 nm)] were improved with an increase in chromophore content. The PFG4 device revealed the best performance (6790 cd/m², 1.69 cd/A), and the PFG1 and PFG2 devices exhibited comparable intensity in blue and green emissions. Blend EL devices were fabricated by using the PFGn as the hosts and a red iridium complex [Ir(piq)₂(acac)] as dopant. By controlling the amount of the iridium complex, the white‐light emitting device was achieved with PFG2 , with maximum brightness and CIE coordinate being 4120 cd/m² and (0.31, 0.28), respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 149–160, 2009     

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

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

Synthesis and optoelectronic properties of luminescent poly(p‐phenylenevinylene) derivatives containing electron‐transporting 1,3,4‐oxadiazole groups

Three random copolymers ( P1–P3 ) comprising phenylenevinylene and electron‐transporting aromatic 1,3,4‐oxadiazole segments (11, 18, 28 mol %, respectively) were prepared by Gilch polymerization to investigate the influence of oxadiazole content on their photophysical, electrochemical, and electroluminescent properties. For comparative study, homopolymer poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐p‐phenylenevinylene] ( P0 ) was also prepared by the same process. The polymers ( P0–P3 ) are soluble in common organic solvents and thermally stable up to 410 °C under a nitrogen atmosphere. Their optical properties were investigated by absorption and photoluminescence spectroscopy. The optical results reveal that the aromatic 1,3,4‐oxadiazole chromophores in P1–P3 suppress the intermolecular interactions. The HOMO and LUMO levels of these polymers were estimated from their cyclic voltammograms. The HOMO levels of P0–P3 are very similar (?5.02 to ?5.03 eV), whereas their LUMO levels decrease readily with increasing oxadiazole content (?2.7, ?3.08, ?3.11, and ?3.19 eV, respectively). Therefore, the electron affinity of the poly(p‐phenylenevinylene) chain can be gradually enhanced by incorporating 1,3,4‐oxadiazole segments. Among the polymers, P1 (11 mol % 1,3,4‐oxadiazole) shows the best EL performance (maximal luminance: 3490 cd/m², maximal current efficiency: 0.1 cd/A). Further increase in oxadiazole content results in micro‐phase separation that leads to performance deterioration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4377–4388, 2007     

Luminescent copoly(aryl ether)s consisting of alternate oxadiazole and 1,4‐distyrylbenzene derivatives: Synthesis and characterization

In an effort to decrease the electron‐injection barrier from the anode electrode, four copoly(aryl ether)s ( P1 – P4 ), consisting of alternating isolated electron‐transporting [2,5‐diphenyl‐1,3,4‐oxadiazole for P1 and P3 and 5,5′‐diphenyl‐2,2′‐p‐(2,5‐bishexyloxyphenylene)‐bis‐1,3,4‐oxadiazole for P2 and P4 ] and emitting chromophores (1,4‐distyryl‐2,5‐dihexyloxybenzene for P1 and P2 and 1,4‐distyryl‐2,5‐dihexylbenzene for P3 and P4 ), have been synthesized by the nucleophilic displacement reaction between bisfluoride and bisphenol monomers. They are basically amorphous materials with 5% weight‐loss temperature above 400 °C. The photoluminescence spectra and quantum yields of these copolymers are dependent on the compositions of the two isolated fluorophores. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of these copolymers have been estimated from their cyclic voltammograms. All the observations directly prove that the oxidation starts at the hole‐transporting segments. The electron affinity can be enhanced by the introduction of isolated electron‐transporting segments that lead to a charge‐injection balance. Single‐layer light‐emitting diodes (Al/ P1 – P4 /ITO glass) have been fabricated. P1 and P2 reveal blue electroluminescence, and P3 and P4 reveal purple‐blue electroluminescence. Moreover, the incorporation of bisoxadiazole units increases the electron affinity and reduces the turn‐on electric field better than one oxadiazole unit. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2765–2777, 2003     

Pyrenoimidazole‐Based Deep‐Blue‐Emitting Materials: Optical,Electrochemical, and Electroluminescent Characteristics

A series of pyrenoimidazoles that contained various functional chromophores, such as anthracene, pyrene, triphenylamine, carbazole, and fluorene, were synthesized and characterized by optical, electrochemical, and theoretical studies. The absorption spectra of the dyes are dominated by electronic transitions that arise from the pyrenoimidazole core and the additional chromophore. All of the dyes exhibited blue‐light photoluminescence with moderate‐to‐high quantum efficiencies. They also displayed high thermal stability and their thermal‐decomposition temperatures fell within the range 462–512 °C; the highest decomposition temperature was recorded for a carbazole‐containing dye. The oxidation propensity of the dyes increased on the introduction of electron‐rich chromophores, such as triphenylamine or carbazole. The application of selected dyes that featured additional chromophores such as pyrene, carbazole, and triphenylamine as blue‐emissive dopants into multilayered organic light‐emitting diodes with a 4,4′‐bis(9H‐carbazol‐9‐yl)biphenyl (CBP) host was investigated. Devices that were based on triphenylamine‐ and carbazole‐containing dyes exhibited deep‐blue emission (CIE 0.157, 0.054 and 0.163, 0.041), whereas a device that was based on a pyrene‐containing dye showed a bright‐blue emission (CIE 0.156, 0.135).     

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.     

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     

Optical and electroluminescent properties of novel poly(aryl ether)s with isolated carbazole and p‐quaterphenyl fluorophores

We report the optical and electroluminescent properties of four novel poly(aryl ether)s ( P1 – P4 ) consisting of alternate isolated hole‐transporting [carbazole or 3,6‐bis(styryl)carbazole] and electron‐transporting [dicyano‐p‐quaterphenyl or bis(trifluoromethyl)‐p‐quaterphenyl] fluorophores. The photoluminescence (PL) spectra of the four polymeric films show maximum peaks around 407–413 nm for P1 , P2 and 442–447 nm for P3 , P4 . The PL spectra of P1 ～ P4 are dependent on the composition of the two isolated fluorophores. According to the observation of relative quantum yield in poor solvent (cyclohexane), P2 containing more bulky trifluoromethyl groups in p‐quaterphenyl segments prevented aggregate quenching processes more than P1 . Compared with P1 and P2 with carbazole segments, P3 and P4 with 3,6‐bis(styryl)carbazole segments exhibited less interchain interaction and a low threshold electric field in a single‐layer device. The p‐quaterphenyl and carbazole [or 3,6‐bis(styryl)carbazole] segments were regarded as electron‐transporting and hole‐transporting units, respectively, in the single‐layer light‐emitting diodes (Al/ P1 – P4 /ITO). In the double‐layer device (ITO/MEH‐PPV/ P2 /Al), the maximum luminance was doubled, and the threshold electric fields diminished because P2 functioned as an electron‐transporting and hole‐blocking layer. Furthermore, the voltage‐tunable multicolor emission from orange to green was observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 333–340, 2004     

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     

Luminescent copolyethers containing isolated 1,4‐distyrylbenzene derivatives backbone and 7‐oxy‐4‐methylcoumarin side group: Synthesis and characterization

Four new copolyethers ( P1 – P4 ) consisting of two isolated emitting chromophores [2,5‐dihexyloxy‐1,4‐distyrylbenzene (HODSB) and 2,5‐dihexyloxy‐1,4‐di(4‐methylenestyryl)benzene (HOMDSB) for P1 and P2 , 2,5‐dihexyl‐1,4‐distyrylbenzene (HDSB) and HOMDSB for P3 and P4 ] in the backbone, in which P2 and P4 further contain electron‐transporting chromophores [7‐oxy‐4‐methylcoumarin (OMC)] in the side chain, were successfully prepared by the Heck coupling reaction. The photoluminescence spectra and quantum yields of the copolymers depended mainly on compositions of the isolated fluorophores. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels were estimated from their cyclic voltammograms. Electrochemical investigations proved that the oxidation started at hole‐transporting DSB segments, whereas reduction began at electron‐transporting OMC groups in P2 and P4 . The electron affinity of P2 and P4 was enhanced by introducing electron‐transporting OMC chromophores. Double‐layer light‐emitting diodes (ITO/PEDOT:PSS / polymer/Al) of P1 and P2 revealed green electroluminescence, and those of P3 and P4 emitted blue light. Moreover, incorporation of OMC side groups effectively reduced turn‐on electric field and enhanced luminance efficiency of the EL devices due to increased electron affinity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 211–221, 2007     

Monochromatic‐red‐light emission of novel copolymers containing carbazole units and europium–acrylate complexes

Nearly monochromatic‐red‐light‐emitting polymers with pendant carbazole and europium (Eu) complex were synthesized and characterized by Fourier transform infrared, elemental analysis (EA), ¹H NMR, ¹³C NMR, UV, and gel permeation chromatography. The photoluminescence and electroluminescence (EL) properties of these polymers were investigated. A single‐layer light‐emitting‐diode device of the structure (indium tin oxide/polymer P4/Al) was fabricated, showing the characteristic bright‐red EL of the Eu³⁺ complex at 614 nm at a turn‐on voltage of about 17 V. The EL spectrum, current–voltage, and emission‐intensity–voltage characteristics of the device were measured. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3405–3411, 2000     

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     

Bipolar copoly(aryl ether) containing distyrylbenzene,triphenylamine, and 1,2,4‐triazole moieties: Synthesis and optoelectronic properties

A novel copoly(aryl ether) ( P1 ) consisting of alternate emitting segments (distyrylbenzene) and a bipolar moiety composed of directly linked electron‐transporting aromatic 1,2,4‐triazole and hole‐transporting triphenylamine was synthesized. The copoly(aryl ether) is readily soluble in common organic solvents and exhibit good thermal stability with thermal decomposition temperature above 450 °C. The emission and the photoluminescence quantum yield of the copolymer are dominated by the emitting segments (distyrylbenzene) with longer emissive wavelength. Electron affinity of P1 is evidently enhanced after introducing the isolated bipolar unit, as confirmed by the lowered lowest unoccupied molecular orbital level (–2.77 eV) relative to P0 without bipolar unit (–2.34 eV). This results in improved emission efficiency of its polymer light‐emitting diode (indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/ P1 /LiF/Ca/Al) due to more balanced charges injection and transport. Blending P1 with poly(9,9‐dihexylfluorene) ( PF ) further improves the efficiency of the device; the best performance was obtained for PF / P1 = 20/0.8 (w/w) with maximum luminance and maximum luminance efficiency being significantly enhanced to 3260 cd/m² and 1.08 cd/A, respectively, from 380 cd/m² and 0.009 cd/A of P1 ‐based device. These results demonstrate that the bipolar moiety can be used to enhance charges injection and transport of electroluminescent polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

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     

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     

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