Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)₃] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)₃ emission and the cross reaction of PVK^+·/Ir(ppy)⁻₃ showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)₃ light emitting shows that reaction between PVK^+· and Ir(ppy)⁻₃ is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)₃, while the reaction between Ir(ppy)⁺₃ and PBD^{− ·} is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)₃ and PVK or PBD is sufficient to produce the excited state of Ir(ppy)₃ in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)₃. These results obtained will provide further insight into charge‐transfer excitation in PLEDs.     

Synthesis and characterization of light‐emitting oligo(p‐phenylene‐vinylene)s and polymeric derivatives containing three‐ and five‐conjugated phenylene rings. II. Electro‐optical properties and optimization of PLED performance

A series of multilayer polymeric light‐emitting diodes (PLEDs) containing an electron‐transporting layer (ETL), that is tris(8‐quinolinolato)‐aluminum(III) (Alq) and 2,2′,2″‐(1,3,5‐phenylene)‐tris[1‐phenyl‐1H‐benzimidazole] (TPBI), were fabricated by doping fluorescent oligo(p‐phenylene‐vinylene)s (BIII and BV) and polymer derivatives (PBV) into poly(N‐vinyl carbazole) (PVK). These PLEDs can be optimized by the design of multilayer device configurations (brightness increased 8–15 times by addition of ETL) and possess greenish electroluminescent (EL) spectra peaked about 500–540 nm. A remarkably high brightness of 56,935 cd/m² with a power efficiency of 3.25 lm/W was obtained in the device of PVK:BVOC₈‐OC₈ (100:20)/Alq (60 nm/60 nm). It suggests that the emission mechanism (including the conjugated and excimer emissions of BVOC₈‐OC₈ emitters) originates from both of BVOC₈‐OC₈ and ETL (Alq and TPBI) by varying the concentration of chromophores and adjusting the thickness of ETL. The concentration effect of the emitters in PVK (i.e. PVK:BVOC₈‐OC₈ = 100:5, 100:20, and 100:100 wt %) and the influence of the ETL (including its thickness) on the EL characteristics are also reported. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2922–2936, 2006     

New host homopolymers containing pendant triphenylamine derivatives: Synthesis,optical, electrochemical properties and its blend with Ir(ppy)3 for green phosphorescent organic light‐emitting devices

Two vinyl homopolymers poly(N‐(4‐(4‐(4‐vinylbenzyloxy)styryl)phenyl)‐N‐phenylbenzenamine) (PVST ) and poly(4‐vinyltriphenylamine) (PTPA ) containing pendant hole‐transporting triphenylamine and 4‐oxystyryltriphenylamine groups, respectively, were synthesized by radical polymerization and employed as hosts for tris(2‐phenylpyridine) iridium [Ir(ppy)₃] phosphor. Structural influences of the hole‐transporting groups upon optoelectronic properties were investigated by photophysical, electrochemical, and electroluminescent methods. The polymers were readily soluble in common organic solvents and their weight‐average molecular weights (M_w) were 5.68 × 10⁴ and 1.90 × 10⁴, respectively. The emission spectra (both photoluminescence, PL and electroluminescent, EL) of the blends [PTPA with 4 wt % Ir(ppy)₃] showed dominant green emission (517 nm) attributed to Ir(ppy)₃ due to efficient energy transfer from PTPA to Ir(ppy)₃. The HOMO levels of PVST and PTPA, estimated from onset oxidation potentials in their cyclic voltammograms, were ?5.14 and ?5.36 eV, which are much higher than ?5.8 eV of the conventional poly(9‐vinylcarbazole) (PVK) host owing to high hole‐affinity of the triphenylamine groups. The optoelectronic performances of phosphorescent EL devices, using PVST and PTPA as hosts and Ir(ppy)₃ as dopant (indium tin oxide, ITO/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS)/PVST or PTPA:Ir(ppy)₃(4 wt %):PBD(40 wt %)/BCP/Ca/Al), were investigated. The maximum luminance and luminance efficiency of the PTPA device were 9220 cd/m² and 6.1 cd/A, respectively, which were significantly improved relative to those of PVK and PVST. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7960–7971, 2008     

Synthesis and properties of σ–π conjugated alternating polymers consisting of carbazole and organosilicon units

We have synthesized novel σ–π conjugated polymers with an alternating organosilanylene and π‐electron system, intending to utilize them for hole‐transporting materials of electroluminescent (EL) devices. 3,6‐Di(lithioethynyl)carbazoles were co‐polymerized with organodichlorosilanes to give the corresponding polymers with molecular weights of M_W = 2000–5000. Another type of polymer with a thienylene unit was also synthesized by the nickel‐catalyzed reaction of the di‐Grignard reagent of 1,2‐bis[2‐(5‐bromothienyl)]tetraethyldisilane with 3,6‐dibromocarbazole, the molecular weight being M_n = 3100. The EL devices with a double‐layer system composed of tris(8‐quinolinolato)aluminum(III) and the present polymers as the emitting‐electron‐transporting and hole‐transporting layers, respectively, emit green EL with a maximum intensity of the order of 10³ cd m^?2. Of these, the device with the thienylene–carbazole polymers exhibited the highest luminance of 1480 cd m^?2. Copyright © 2001 John Wiley & Sons, Ltd.     

Cascade hole transport in efficient green phosphorescent light‐emitting devices achieved by layer‐by‐layer solution deposition using photocrosslinkable‐conjugated polymers containing oxetane side‐chain moieties

A hole‐injection/transport bilayer structure on an indium tin oxide (ITO) layer was fabricated using two photocrosslinkable polymers with different molecular energy levels. Two photoreactive polymers were synthesized using 2,7‐(or 3,6‐)‐dibromo‐9‐(6‐((3‐methyloxetan‐3‐yl)methoxy)hexyl)‐9H‐carbazole) and 2,4‐dimethyl‐N,N‐bis(4‐ (4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)phenyl)aniline via a Suzuki coupling reaction. When the oxetane groups were photopolymerized in the presence of a cationic photoinitiator, the photocured film showed good solvent resistance and compatibility with a poly(N‐vinylcarbazole) (PVK)‐based emitting layer. Without the use of a conventional hole injection layer (HIL) of poly(3,4‐ethylenedioxythiophene)/(polystyrenesulfonate) (PEDOT:PSS), the resulting green light‐emitting device bearing PVK: 5‐4‐tert‐butylphenyl‐1,3,4‐oxadiazole (PBD):Ir(Cz‐ppy)3 exhibited a maximum external quantum efficiency of 9.69%; this corresponds to a luminous efficiency of 29.57 cd/A for the device K‐4 configuration ITO/POx‐I/POx‐II/PVK:PBD:Ir(Cz‐ppy)3/triazole/Alq3/LiF/Al. These values are much higher than those of PLEDs using conventional PEDOT:PSS as a single HIL. The significant improvement in device efficiency is the result of suppression of the hole injection/transport properties through double‐layered photocrosslinked‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Photoluminescence and Electroluminescence Properties of 2,5-Bis[2,2′-bis(5-phenyl)-1,3,4-oxadiazole] Thiophene(T-OXD)and T-OXD/Poly(9-vinylcarbazole) Blends

The photoluminescence(PL) and the electroluminescence(EL) properties of a novel organic compound, 2,5-bis(2,2′-bis(5-phenyl)-1,3,4-oxadiazole(T-OXD), were studied in chloroform and in a solid thin film. The PL and the EL properties of T-OXD/poly(9-vinylcarbazole)(PVK) blends were also studied, which contained various contents of T-OXD. The PL maximum emission peaks of T-OXD/PVK blends show gradual bathochromtic-shift with the increase of the T-OXD content. The EL spectra of T-OXD/PVK devices are similar to their PL spectra, and all the EL maximum emission peaks show bathochromtic-shift compared with the corresponding PL spectra, which is ascribed to the formation of electroplex. The turn-on voltages for ITO/T-OXD:PVK/Al devices decreased from 13.5 V of the device cotaining 0.1% T-OXD(mass fraction) to 5 V of the device containing 5% T-OXD, which suggests that T-OXD improves the energy level match between T-OXD and PVK and enhances the emission efficiency. The experimental results indicate that T-OXD can be used as a good electron transporting material.     

Luminescence properties of poly(p‐phenylenevinylene) derivatives carrying directly attached hole‐transporting carbazole and electron‐transporting phenyloxadiazole pendants

New poly(p‐phenylenevinylene) (PPV) derivatives ( polymer 1 and 2 ) that carry hole‐transporting carbazole and electron‐transporting phenyloxadiazole pendants were synthesized and their photo‐ and electroluminescence properties were studied. Polymer 1 is poly[2‐(N‐carbazolyl)‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] that has both carbazole and 2‐ethylhexyl pendant groups. And polymer 2 is poly[2‐{4‐[5‐(4‐t‐butylphenyl)‐1,3,4‐oxadiazolyl]phenyl}‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene], which bears the 2‐(4‐t‐butylphenyl)‐5‐phenyl‐1,3,4‐oxadiazole pendants. The optical properties of the polymer films were studied by UV‐vis absorption, photoluminescence (PL) and electroluminescence (EL) spectroscopy. EL devices with the configuration of ITO/poly(3,4‐ethylenedioxy‐2,5‐thienylene) (PEDOT) polymer/Ca/Al were constructed and the device performances were compared. Polymer 1 emits bright yellowish green light (λ_max = 530 nm), whereas polymer 2 emits yellowish orange (λ_max = 540 nm) light. The device fabricated using polymer 1 showed a low turn‐on electric field of 0.31 MV/cm and the maximum luminance of 30,390 cd/m² at 1.50 MV/cm. Polymer 2 exhibited a little poorer device performance (turn‐on electric field: 0.94 MV/cm; maximum luminance: 5,720 cd/m² at 2.74 MV/cm). Maximum photometric efficiencies of the devices were 4.4 and 1.3 cd/A, respectively.     

Organic electroluminescent devices using organosilicon polymers containing phenylene or diethynylanthracene units

Double‐layer electroluminescent (EL) devices composed of an alternating polymer with mono‐, di‐, or tri‐silanylene and phenylene units, [(Si R) _m (C₆H₄)] _n (R = alkyl, m = 1–3) as a hole‐transporting layer, and tris(8‐quinolinolato)­aluminium(III) complex (Alq) as an electron‐transporting–emitting layer were fabricated. The longer silanylene chain lengths in the polymer, on going from m = 1 to m = 2 and 3, result in better electrical properties for the EL devices, implying that the σ–π conjugation in the polymers plays an important role in the hole‐transporting properties, including the hole‐injection efficiency from an anode. This is in marked contrast to the improved hole‐transporting properties that occur in response to reducing the silanylene chain length of silanylene‐diethynylanthracene polymers previously reported. The UV absorption maxima of silanylene‐phenylene polymers shift to longer wavelengths with increasing m, and their oxidation peak potentials in cyclic voltammograms shift to lower potential with increasing m, in accordance with the improved electrical properties of the device that are observed with the polymers containing the longer silanylene chain. A triple‐layer EL device with a hole‐transporting layer of monosilanylene‐diethynylanthracene polymer, an electron‐transporting–emitting layer of Alq, and an electron‐blocking layer of N,N′‐diphenyl‐N,N′‐bis(3‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine (TPD) exhibited a maximum efficiency of 1.0 lm W⁻¹ and a maximum luminance of 14750 cd m⁻², both of which are much higher than the values obtained from a conventional EL device with TPD/Alq. Copyright © 1999 John Wiley & Sons, Ltd.     

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     

Deep‐red light‐emitting phosphorescent dendrimer encapsulated tris‐[2‐benzo[b]thiophen‐2‐yl‐pyridyl] iridium (III) core for light‐emitting device applications

New deep‐red light‐emitting phosphorescent dendrimers with hole‐transporting carbazole dendrons were synthesized by reacting tris(2‐benzo[b]thiophen‐2‐yl‐pyridyl) iridium (III) complex with carbazolyl dendrons by DCC‐catalyzed esterification. The resulting first‐, second‐, and third‐generation dendrimers were found to be highly efficient as solution‐processable emitting materials and for use in host‐free electrophosphorescent light‐emitting diodes. We fabricated a host‐free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m² at 383.4 mA/cm² (12 V) for 15 , 1302 cd/m² at 321.3 mA/cm² (14 V) for 16 , and 422 cd/m² at 94.4 mA/cm² (18 V) for 17 . The third‐generation dendrimer, 17 (η_ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light‐harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep‐red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable materials for dendrimer light‐emitting diode (DLED) applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517–7533, 2008     

Performance Improvement of Organic Light Emitting Diodes Using Poly(N-vinylcarbazole) (PVK) as a Blocking Layer

High efficiency organic light‐emitting‐devices (OLED) have been fabricated by incorporation of a polymeric layer as a controller of the unbalanced charge. In device configuration of ITO/PEDOT:PSS/PVK/Alq₃/LiF:Al, poly(N‐vinylcarbazole) (PVK) was selected as a block‐ing layer (BL) because it has a hole transporting property and a higher band gap, especially a lower LUMO level than the emitting layer (Alq₃) and a higher HOMO level than the hole injection layer (PEDOT: PSS). As a result, the optimal structure with this bl layer showed a peak efficiency of 6.89 cd/A and 2.30 lm/W compared to the device without the PVK layer of 1.08 cd/A, 0.27 lm/W. This result shows that the PVK layer could effec‐tively block the electrons from metal cathode and confine them in the emitting layer and accomplish the charge balance, which leads to enhanced hole‐electron balance for achieving high recombination efficiency.     

稀土配合物Eu(DBM)3为发光体的有机电致发光器件

分别以稀土配合物为发光中心，以PPV、Alq3为空穴输送层和电子输送层制备了结构为ITO／PPV／PVK：PBD：Eu（DBM）3／Alq3／Al的电致发光器件，其中发射层由旋涂法形成，该器件的最大亮度为52cd·m－2，且具有很好的单色性。     

Organic electroluminescent devices using europium complex‐doped poly(N‐vinylcarbazole)

Electroluminescence (EL) properties of europium (Eu) complex‐doped poly(N‐vinylcarbazole) (PVK) were investigated. A device structure of glass substrate/indium‐tin oxide/hole‐injection layer/Eu complex‐doped PVK/hole‐blocking layer/electron transport layer/electron‐injection layer/Al was employed. Red emission originating from Eu complex was observed. Relatively high luminance of 50 cd/m² and an efficiency of 0.2% were obtained. Copyright © 2004 John Wiley & Sons, Ltd.     

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     

Poly(N‐vinylcarbazole) chemically modified graphene oxide

A new soluble donor‐acceptor type poly(N‐vinylcarbazole)‐covalently functionalized graphene oxide (GO‐PVK) has been synthesized by reaction of DDAT (S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid)trithiocarbonate)‐PVK with GO‐toluene‐2,4‐diisocynate. The incorporation of sufficient amount of PVK chains makes the modified GO nanosheets readily dispersible in organic solvents. The resulting material exhibits an enhanced solubility of 10 mg/mL in organic solvents. Covalent grafting of PVK onto the edge and surface of GO nanosheets did not change the carbazole absorption in the ultraviolet region, but substantially reduced the absorption intensity of GO in the visible region. The intensity of the emission band of GO‐PVK at 437 nm was a little bit quenched when compared with that of DDAT‐PVK, suggesting intramolecular quenching from PVK to GO. Such intramolecular quenching process may involve energy or electron transfer between the excited singlet states of the PVK moiety and the GO moiety. The HOMO/LUMO values and the energy bandgap of GO‐PVK experimentally estimated by the onset of the redox potentials are ?5.60, ?3.58, and 2.02 eV, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2642–2649, 2010     

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     

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     

Highly soluble green‐emitting Ir(III) complexes with 9‐(6‐phenyl‐pyridin‐3‐ylmethyl)‐9H‐carbazole ligands and their application to polymer light‐emitting diodes

Highly organic soluble Ir(III) complexes with 9‐(6‐phenyl‐pyridin‐3‐ylmethyl)‐9H‐carbazole were simply synthesized, and the solubility of the new complex was significantly improved when compared with the conventional green‐emitting Ir(ppy)₃. Since a carbazole group is tethered through a nonconjugated methylene spacer, the photophysical properties of new complexes are almost identical with those of conventional Ir(ppy)₃. The pure complexes were utilized to prepare electrophosphorescent polymer light‐emitting diodes (PLEDs). The device performances were observed to be relatively better or comparable with those of Ir(ppy)₃ based poly(N‐vinylcarbazole) systems. The integration of rigid hole‐transporting carbazole and phosphorescent complex provides a new route to design highly efficient solution‐processable complex for electrophosphorescent PLED applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7419–7428, 2008     

Synthesis and characterization of polyfluorenevinylene with cyano group and carbazole unit

The present investigation deals with the synthesis, characterization, and EL properties of new polyfluorenevinylenes, CzCNPFVs, with cyano‐substituted vinylene unit and carbazole pendant. In CzCNPFVs, synthesized by the Knoevenagel condensation, the carbazole pendant was introduced to improve the efficiency of reported CNPFV. The PL emission spectra of the CzCNPFVs in chloroform solution show maximum peaks at 476–479 nm. In thin films, maximum peaks of the CzCNPFVs appeared at 501–504 nm, red‐shifted around 25 nm as compared to those in solution. The emission maxima of the EL spectra of the polymers appear at around 496–504 nm. The maximum luminescence (L_max) of CzCNPFV2 of the device with the configuration of ITO/PEDOT/CzCNPFVs/Ca/Al is 1724 cd/m² at 8 V. The maximum luminescence efficiency of CzCNPFV1 is 0.18 cd/A. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6540–6551, 2009     

The Control of Conjugation Lengths and Steric Hindrance to Modulate Aggregation‐Induced Emission with High Electroluminescence Properties and Interesting Optical Properties

A series of novel AIE‐active (aggregation‐induced emission) molecules, named SAF‐2‐TriPE, SAF‐3‐TriPE, and SAF‐4‐TriPE, were designed and synthesized through facile reaction procedures. We found that incorporation of the spiro‐acridine‐fluorene (SAF) group, which is famous for its excellent hole‐transporting ability and rigid structure, at different substitution positions on the phenyl ring affected the conjugation lengths of these compounds. Consequently, we have obtained molecules with different emission colors and properties without sacrificing good EL (electroluminescence) characteristics. Accordingly, a device that was based on compound SAF‐2‐TriPE displayed superior EL characteristics: it emitted green light with η_{c, max}=10.5 cd A^?1 and η_{ext, max}=4.22 %, whereas a device that was based on compound SAF‐3‐TriPE emitted blue‐green light with η_{c, max}=3.9 cd A^?1 and η_{ext, max}= 1.71 %. These compounds also displayed different AIE performances: when the fraction of water in the THF solutions of these compounds was increased, we observed a significant improvement in the Φ_F of compounds SAF‐2‐TriPE and SAF‐3‐TriPE; in contrast, compound SAF‐4‐TriPE showed an abnormal phenomenon, in that it emitted a strong fluorescence in both pure THF solution and in the aggregated state without a significant change in Φ_F. Overall, this systematic study confirmed a relationship between the regioisomerism of the luminophore structure and its AIE activity and the resulting electroluminescent performance in non‐doped devices.