Synthesis and luminescence of red,fluorinated iridium (III) complexes containing alkenyl benzothiazole ligand

Two novel iridium(III) complexes (2-FSBT)₂Ir(acac) and (4-FSBT)₂Ir(acac) (2-FSBT, (E)-2-(2-fluorostyryl)benzo[d]thiazole; 4-FSBT, (E)-2-(4-fluorostyryl)benzo[d]thiazole; acac, acetylacetone) were synthesized and characterized by ¹H NMR and mass spectrometry. The organic light emitting diodes based on these complexes with the structure of ITO/m-MTDATA(10 nm)/NPB(20 nm)/CBP:Ir-complex(X %, 30 nm)/BCP(10 nm)/Alq₃(30 nm)/LiF(1 nm)/Al(100 nm) were fabricated. The device based on (2-FSBT)₂Ir(acac) exhibited a maximum efficiency of 9.32 cd/A, a luminance of 8800 cd/cm²; and the device based on (4-FSBT)₂Ir(acac) showed a maximum efficiency of 8.5 cd/A, a luminance of 6986 cd/cm². The Commission International de L’Eclairage (CIE) coordinates (1931) of these complexes were (0.619, 0.381) and (0.621, 0.378), respectively.     

High color rendering white organic light-emitting diodes fabricated using a broad-bandwidth red phosphorescent emitter for lighting applications

High color rendering white organic light-emitting devices (WOLEDs) were developed using a broad-bandwidth red phosphorescent iridium complex, bis[2-(1-naphthyl)benzothiazolato-N,C²′]iridium(III) acetylacetonate [Ir(absn)₂(acac)]. The red phosphorescent emitter Ir(absn)₂(acac) was used to fabricate blue–red and blue–green–red WOLEDs by combining blue-emitting bis[2-(4,6-difluorophenyl)pyridinato-N,C²′]iridium(III) picolinate (FIrpic) and green-emitting tris-fac-(2-cyclohexenylpyridine) iridium (III) [Ir(chpy)₃] in multiple-emissive layers. Mixed host emissive layers were employed using a hole-transport-type host 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) and an electron-transport-type host 2,6-bis[3-(carbazol-9-yl)phenyl]pyridine (DCzPPy) for efficient charge carrier injection. Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) and 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB) were used as the hole and electron transporting layers, respectively. The effects of the emissive layer thickness and the doping ratios of different color dopants on WOLED performances were investigated. The WOLED based on ITO/TAPC/TCTA:FIrpic (10%):Ir(absn)₂(acac) (4%)/TCTA:Ir(chpy)₃ (9%, 6 nm)/DCzPPy:FIrpic (13%):Ir(absn)₂(acac) (4%)/BmPyPB/LiF/Al exhibited an external quantum efficiency of 10.7%, a power efficiency of 23.0 lm/W, a very high color rendering index (CRI) of 88.1, and a correlated color temperature (CCT) of 2629 K at 1000 cd/m².     

Synthesis,photoluminescent and electroluminescent properties of a novel europium(III) complex involving both hole- and electron-transporting functional groups

A novel europium(III) complex involving a carbazole fragment as hole-transporting group and an oxadiazole fragment as electron-transporting group was synthesized and used as red light-emitting material in organic light-emitting diodes (OLEDs). The complex is amorphous, and exhibits high glass transition temperature (T_g = 157 °C) and high thermal stability with a 5% weight loss temperature of 367 °C. Two devices, device 1: ITO/NPB (40 nm)/Eu(III) complex (30 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) and device 2: ITO/NPB (40 nm)/3% Eu(III) complex: CBP (30 nm)/BCP (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm), were fabricated, where NPB is N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine, Alq₃ is tris(8-hydroxyquinoline) Al(III), CBP is 4,4′-bis(carbazole-9-yl)-biphenyl, and BCP is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, respectively. In contrast with device 1, owing to less self-quenching and better charge confinement, device 2 shows improved performances: the maximum luminance of device 2 was dramatically increased from 199 to 1845 cd/m², the maximum current efficiency was increased from 0.69 to 2.62 cd/A, the turn-on voltage was decreased from 9.5 to 5.5 V, and higher color purity was attained.     

Iridium(III) complexes with cyclometalated styrylbenzoimidazole ligands: Synthesis,electrochemistry and as highly efficient emitters for organic light-emitting diodes

Two phosphorescent iridium complexes (psbi)₂Ir(acac) and (ppbi)₂Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)₂Ir(acac) exhibited a maximum brightness of 56,162 cd m^?2, while the device based on (ppbi)₂Ir(acac) gave a maximum brightness of 31,232 cd m^?2. At high brightness of 1000 cd m^?2 and 10,000 cd m^?2, high current efficiencies of 25.7 cd A^?1 and 20.7 cd A^?1 were achieved, respectively, for the (psbi)₂Ir(acac)-based EL device. For the EL device based on (ppbi)₂Ir(acac), current efficiencies of 20.1 cd A^?1 at 1000 cd m^?2 and 14.2 cd A^?1 at 10,000 cd m^?2 were observed.     

Solution processable organic electro-phosphorescent iridium complex based on a benzothiazole derivative

We have synthesized a new solution processable iridium complex, di[2-(4′-octyloxyphenyl) benzothiazole]iridium(III)acetoacetone, [(OPBT)₂Ir(acac)], based on benzothiazole derivative for organic electro-phosphorescent devices. The synthesized molecule was identified by ¹H NMR and ¹³C NMR, and readily soluble in common organic solvents such as chlorobenzene. The UV–visible absorption and photoluminescence properties of pristine [(OPBT)₂Ir(acac) thin film as well as poly(N-vinylcarbzole) (PVK) thin film doped with the iridium complex were studied. The maximum UV–visible absorption and photoluminescence (PL) spectra are found to be at 337 nm and 547 nm, respectively. We have fabricated phosphorescent organic light-emitting devices using the ITO/PEDOT:PSS (40 nm)/PVK:(OPBT)₂Ir(acac) (40 nm)/Balq (40 nm)/LiF (1 nm)/Al (80 nm) configuration with the iridium complex as a triplet emissive dopant in poly(N-vinylcarbazole) (PVK) host. The electroluminescence (EL) devices showed greenish yellow light emission with maximum peak at 551 nm. Especially, the maximum external quantum and current efficiency of 1 mol% doped device were 1.74% and 4.89 cd/A, respectively.     

Organic light-emitting devices with triphenylphosphine oxide layer

We have developed organic light-emitting devices using triphenylphosphine oxide (Ph₃PO) layers. The operating voltage of device is substantially reduced by using a Ph₃PO layer. For example, the required voltages for a current density of 20 mA/cm² are 3.5 and 9.7 V for the devices with Ph₃PO and Alq₃ layers, respectively. Good electron transporting property of Ph₃PO results in a high luminance of 1000 cd/m² at a low driving voltage of 4.1 V in a device with a structure of ITO/2-TNATA (15 nm)/α-NPD:rubrene (1%, 10 nm)/α-NPD (30 nm)/Ph₃PO (60 nm)/LiF (0.5 nm)/Al.     

Low driving voltage and efficient orange-red phosphorescent organic light-emitting devices based on a benzotriazole iridium complex

Efficient orange-red phosphorescent organic light-emitting devices (PHOLED) with various doping concentrations of benzotriazole–iridium complex [(TBT)₂Ir(acac)] (bis[4-(2H-benzotriazol-2-yl)-N,N-diphenyl-aniline-N¹,C³] iridium acetylacetonate) in 4,4′-N,N′-di(carbazolyl) biphenyl (CBP) host were fabricated. The sterically hindered iridium ligands alleviate self-quenching of the phosphorescence at high doping levels. Under the optimal doping concentration of 20 wt.%, the maximum external quantum efficiency (EQE), luminance and power yield reach 9.06%, 15.81 cd/A and 13.8 lm/W, respectively. Increasing the doping concentration from 5% to 30 wt.% significantly decreases the driving voltage. The driving voltage of 30% (TBT)₂Ir(acac) doped device is only 3.16 V at 1 mA/cm² with power yield of 13.32 lm/W.     

Synthesis,photophysical and electrophosphorescent properties of a novel fluorinated rhenium(I) complex

A novel fluorinated rhenium complex, i.e., Re-BFPP (BFPP, 2, 3-bis(4-fluorophenyl)pyrazino[2,3-f][1,10]phenanthroline) was designed, synthesized and characterized by ¹H NMR and mass spectroscopy. The light-emitting and electrochemical properties of this complex were studied. The organic light-emitting diodes (OLEDs) employing Re-BFPP as a dopant emitter with the structures of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: X wt.% Re-BFPP (30 nm)/Bphen (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) were successfully fabricated and a broad electroluminescent peak at 553 nm was observed. The 10 wt.% Re-BFPP doped device exhibited the maximum luminance of 6342 cd/m² and a peak current efficiency of 17.9 cd/A, corresponding to the power efficiency of 8.1 lm/W.     

Bis(arylquinoxalinyl)carbazole derivatives as saturated blue emitters for electroluminescent devices

Bis(arylquinoxalinyl)carbazole derivatives 9-phenyl-3,6-bis-(3-phenyl-quinoxalin-2-yl)-9H-carbazole (PPQC), 9-phenyl-3,6-bis-[3-(4-methoxy-phenyl)-quinoxalin-2-yl]-9H-carbazole (PMQC) and 9-phenyl-3,6-bis-(3-p-tolyl-quinoxalin-2-yl)-9H-carbazole (PTQC) were conveniently synthesized from the corresponding tetraone and o-phenylenediamine. Electroluminescent devices using PTQC as the dopant emitters were fabricated. These devices all emit saturated blue light from the PTQC doped layer. Device C that consists of CuPc (10 nm)/TCTA (30 nm)/PTQC:TPBI (7%, 30 nm)/TPBI (40 nm) shows the highest performance. The device emits blue light at 446 nm with CIE values of (0.15, 0.08) and shows a maximum external quantum efficiency of 1.31%, current efficiency of 1.00 cd/A, and brightness of 5067 cd/m².     

Efficient electroluminescent tertiary europium(III) β-diketonate complex with functional 2,2′-bipyridine ligand

A new red electroluminescent complex (2Fphen-bpy)Eu(DBM)₃(2Fphen-bpy: 4-(2,4-difluorophenylene)-2,2′-bipyridine; DBM: dibenzoylmethanate) was designed and synthesized. X-ray single crystal structural analysis shows that the dihedral angles involving the difluorophenylene moiety and two pyridine rings of the 2,2′-bipyridine unit in (2Fphen-bpy)Eu(DBM)₃ are 42° and 51.6°, indicant of non-conjugation between the two segments. The europium complex was incorporated into the doped electroluminescent device: ITO/TPD(40 nm)/(2Fphen-bpy)Eu(DBM)₃:CBP(30 nm, 3%)/BCP(20 nm)/Alq₃(30 nm)/LiF(1 nm)/Al(100 nm). At the brightness of 100 cd/m², the current and power efficiency are about 2.53 cd/A and 0.79 lm/W, respectively. In comparison with the inefficient control device using (2,2′-bipyridine)Eu(DBM)₃ as the red emitter in the same configuration, the introduction of difluorophenylene moiety into the Eu(III) complex could possibly account for the improved performance of the title compound.     

Photoluminescence and electroluminescence of 3-methyl-8-dimethylaminophenazine

A new phenazine dye—3-methyl-8-dimethylaminophenazine (MDAP) with intramolecular charge transfer (ICT) property was synthesized. The photoluminescence and electroluminescence of were investigated. The device with a configuration of ITO/TPD (30 nm)/TPD:MDAP (30 nm)/Alq₃:MDAP (35 nm)/Alq₃ (30 nm)/Mg:Ag (200 nm) showed a good performance with a brightness of 21650 cd/m² at 250 mA/cm², a maximum luminous efficiency of 9.97 cd/A and a yellow emission peaked at about 564–586 nm.     

A new family of solution-processible tris-(pinene-phenylpyridine) iridium(III) derivatives for polymer light-emitting diodes

A new family of iridium(III) complexes featuring pinene groups and various alkoxy side chains were synthesized and characterized. The complexes show emission peaked at around 492 nm with the phosphorescence quantum yield of Φ_P = 0.4–0.6 and the emission lifetime of τ = 2–4 μs. Polymer light emitting devices (PLEDs) with the configuration of ITO/PEDOT:PSS (50 nm)/PVK_0.7:PBD_0.3:(x wt.%)Ir(III) complex(80 nm)/CsF(1.5 nm)/Mg:Ag(200 nm) were fabricated by spin-coating. The device with new iridium(III) complex doping concentration of 3.2 wt.% exhibits a maximum luminance efficiency 19.9 cd/A (7.8 lm/W) at 9.1 V, CIE coordinates (0.21, 0.53), and a maximum luminance of 15,700 cd/m² at 8.4 V was observed.     

Highly efficient energy transfer to a novel organic dye in OLED devices

The neutral 4,4-difluoro-8-(2,2′:6′,2″-terpyridine-4′-yl)-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (Boditerpy) molecule was synthesized and incorporated as dopant (<1%) in double-layer organic light emitting diodes (OLEDs) with the configuration ITO/α-NPD(60 nm)/Alq₃(60 nm):Boditerpy (0.4 nm)/LiF(0.02 nm)/Al(80 nm). This device exhibits green emission with a brightness of 545 cd/m² at 8 V and a maximum power efficiency of 0.9 lm/W. A full quantitative energy transfer process is indicated by a complete quenching of light emission from Alq₃ in photoluminescence. However, I–V characteristics indicate some losses during the charge transfer processes in OLED configuration     

White organic light-emitting diodes based on blue fluorescent bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)2] doped with DCM dye

Bright white organic light-emitting diodes (WOLEDs) with single active layer has been demonstrated from blue emitting zinc complex bis(2-(2-hydroxyphenyl)benzoxazolate)zinc [Zn(hpb)₂] doped with orange luminescent 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM) dye. White light electroluminescence (EL) spectrum from Zn(hpb)₂ has been achieved by adjusting the concentration of DCM dye. WOLED with a structure of ITO/α-NPD/Zn(hpb)₂:DCM (x%)/BCP/Alq₃/LiF/Al has been fabricated. The EL spectra covering the whole visible spectra range of 400–700 nm, with two peaks at 446 and 555 nm has been measured. The device emits white light at 10 V with Commission Internationale de I’ Eclairage (CIE) coordinates (0.27, 0.31) and brightness 1083 Cd/m². The maximum current efficiency of the device was 1.23 Cd/A at 9.5 V and maximum luminance reaches 2210 Cd/m² at 12 V.     

Highly efficient red electroluminescence induced by efficient electron injection and exciton confinement

Highly efficient DCJTB-doped device was realized by enhanced electron injection and exciton confinement. A fluorine end-capped linear phenylene/oxadiazole oligomer 2,5-bis(4-fluorobiphenyl-4′-yl)-1,3,4-oxadiazole (1) and a trifluoromethyl end-capped oligomer 2,5-bis(4-trifluoromethylbiphenyl-4′-yl)-1,3,4-oxadiazole (2) were designed and incorporated as an electron transporting/hole blocking material in the device structure ITO/NPB (60 nm)/DCJTB:Alq₃ (0.5%, 10 nm)/1 or 2 (20 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm). The devices showed highly efficient red luminescence. In particular, the device based on 1 achieved pure red luminescence at 620 nm originating from DCJTB, with a narrow FWHI of 65 nm, maximal brightness of 13,300 cd/m² at voltage of 20.8 V and current density of ca. 355 mA/cm². High current and power efficiencies (>3.6 cd/A, 1.0 lm/W) were retained within a wide range of current densities. Our results show efficient and stable DCJTB-doped red electroluminescence could be anticipated for practical applications by taking advantage of the present approaches. The control experiments using BCP were also studied.     

New host materials with high triplet energy level for blue-emitting electrophosphorescent device

A series of new 9-phenylcarbazole (Cz-Ph)-based host materials with 1,2,4-trizole (TAZ) were synthesized for blue-emitting electrophosphorescent device. The substitution position of Cz-Ph on TAZ ring did not influence photoluminescence maximum (band gap) but the triplet energy level (T₁). The electron mobility of 3,5-bis-(3-(9-carbazoyl)-phenyl)-4-(4-butyl-phenyl)-4H-[1,2,4]triazole (6) is 10 times higher than the hole mobility. This is due to the electron transporting/hole blocking characteristics of TAZ moiety. The triplet energy level of the new host materials ranges from 2.8 to 3.0 eV which are suitable for blue-emitting electrophosphorescent devices. The time-resolved photoluminescence decay curve of 4% of FIrpic (iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate) doped in the film of compound 6 showed a single exponential decay curve with a lifetime of 1.2 μs. The absolute PL quantum efficiency (η_PL) of 6 doped with 4% of FIrpic was (82 ± 2%), which is significantly higher than the case of commonly used CBP (4,4′-bis-(9-carbazoyl)-biphenyl) (44 ± 2%). These results also strongly support that triplet excitons formed in FIrpic was not transferred to 6. For a device based on 6 (ITO/PEDOT:PSS (40 nm)/NPB (15 nm)/6:6% FIrpic (30 nm)/BAlq (35 nm)/LiF (1 nm)/Al (100 nm), the maximum photometric efficiency was 14.2 cd/A at a current density of 1.1 mA/cm², which is higher than that observed with a device based on CBP (ITO/PEDOT:PSS (40 nm)/NPB (30 nm)/CBP:6% FIrpic (40 nm)/BAlq (30 nm)/LiF (1 nm)/Al (100 nm)).     

Manufacture of brightness enhancement films (BEFs) by ultraviolet (UV) irradiation and their applications for organic light emitting diodes (OLEDs)

By ultraviolet (UV) irradiation, brightness enhancement films (BEFs) have been successfully manufactured with UV-curable polymers and applied for organic light emitting diodes (OLEDs).With BEFs, either green OLEDs (BEF/ITO glass/NPB (30 nm)/Alq₃ (65 nm)/LiF (0.5 nm)/Al (100 nm)) or white OLEDs (BEF/ITO glass/TAPC (40 nm)/mCP:Os:Firpic mixture (weight ratio = 82:17:1; 25 nm)/BCP (15 nm)/Alq₃ (30 nm)/LiF (0.5 nm)/Al(150 nm)) exhibit better electroluminescent performances than those without BEFs. In case of green OLEDs, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.51-fold and 1.42-fold (at 9 V, 60 mA/cm²) larger than those without BEFs. In case of white OLEDs, moreover, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.28-fold and 1.21-fold (at 9 V, 16 mA/cm²) larger than those without BEFs.     

Highly efficient blue electrophosphorescent devices with a novel host material

Highly efficient blue electrophosphorscent light emitting diodes with a new host material N,N′-dicarbazolyl-1,4-dimethene-benzene (DCB) were demonstrated. The energy transfer mechanism of the host–guest material system consisting of DCB and bis[(4,6-difluorophenyl)-pyridinato-N,C²′] (picolinato) Ir(III) (FIrpic) is an exothermic process. The device with a configuration of indium tin oxide/ N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB)/DCB:FIrpic/4,7-diphenyl-1,10-phenanthroline(BPhen)/Mg:Ag was optimized by adjusting the thickness of emitting layer and the dopant concentration. The device with the 8% (weight ratio) FIrpic and 30 nm emitting layer exhibits the maximum external quantum efficiency and current efficiency of 5.8% and 9.8 cd/A, respectively, at the luminance of 22 cd/m² driven at the voltage of 6.0 V.     

Synthesis,crystal structure,photo- and electro-luminescence of 3-(4-(anthracen-10-yl)phenyl)-7-(N,N′-diethylamino)coumarin

A new coumarin derivative, 3-(4-(anthracen-10-yl)phenyl)-7-(N,N′-diethylamino)coumarin, was synthesized and characterized by FT-IR, ¹H NMR, element analysis and single crystal X-ray crystallography. The dihedral angle of coumarin ring and phenyl group is 30.83°, and the dihedral angle of phenyl group and anthracene skeleton is 76.99°. The photoluminescent (PL) and electroluminescent (EL) properties of the compound were investigated. The results show that the compound exhibits high fluorescence quantum yield (0.83), large Stokes shift and strong blue emission (466 nm). The electroluminescence devices comprised of vacuum vapor-deposited films using the compound as dopant were fabricated, showing blue emission that is identical to its photoluminescent spectrum in chloroform solutions. The electroluminescence device of indium tin oxide (ITO)/4,4′,4″-tris[2-naphthyl (phenyl)-amino]triphenylamine (2-TNATA) (5 nm)/N,N-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (40 nm)/4,4-N,N-dicarbazole-biphenyl (CBP): dopant (1.0 wt%, 30 nm)/2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) (30 nm)/LiF (1 nm)/Al (100 nm) gives a maximum luminous efficiency of 3.3 cd/A at the current density of 20 mA/cm², and maximum luminance of 5070 cd/m² at 16 V.     

White polymer phosphorescent light-emitting devices with a new yellow-emitting iridium complex doped into polyfluorene

A new yellow-emitting iridium complex Ir(3-piq)₂pt with 3-phenylisoquinoline(3-piq) as cyclometalated ligand by introducing 2-(2H-1,2,4-triazol-3-yl)pyridine (pt) as ancillary ligand was synthesized. Efficient yellow polymer light-emitting devices (PLEDs) with the new iridium complex Ir(3-piq)₂pt in device structure ITO/PEDOT/PVK/Ir-complex (x%):PFO (or +PBD (30%))/Ba/Al (with or without PBD electron transports additive) were fabricated. The device doped with 4% Ir(3-piq)₂pt displayed a quantum efficiency of 9.4% (16.2 cd/A) at 5.06 mA/cm² with PBD additive. A white emission was also obtained at a doping concentration of 0.5% Ir(3-piq)₂pt with no PBD added. CIE coordinate (0.34 and 0.31) close to National Television Standards Committee (NTSC) white standard, external quantum efficiency of 2.25%, and luminance of 2250 cd/m² at applied voltage of 15 V were obtained. The results indicated that introducing triazole group based ancillary ligand into iridium complexes could enhance the electron-transporting ability of the iridium complexes.