Novel tri-carbazole modified fluorene host material for highly efficient solution-processed blue and green electrophosphorescent devices

A series of novel solution-processable small-molecule host materials: 2DPF-TCz, 2SBF-TCz, 27DPF-TCz, and 27SBF-TCz comprising a fluorene monomer as the rigid core and tri-carbazole as the periphery have been designed and synthesized, and their optical, electrochemical, and thermal properties have been fully characterized. The host materials exhibit high glass-transition temperatures (231–310 °C) and high triplet energy levels (2.61–2.73 eV). High-quality amorphous thin films can be obtained by spin-coating the host materials from solutions. It is found that the HOMO level of the host materials can be tuned by linking the tri-carbazole unit to the 2,7 positions of the fluorine core, resulting in appropriate HOMO energy levels (−5.36 to −5.23 eV) for improved hole-injection in the device. Solution-processed blue and green electrophosphorescent devices bases on the developed host materials exhibit high efficiencies of 21.2 and 34.8 cd A⁻¹, respectively.     

Recent progress in functionalized electrophosphorescent iridium(III) complexes

Iridium(III) complexes are one of the most important electrophosphorescent dyes with tunable emissions in the range of visible and near infrared lights, high photoluminescence yields and short lifetimes for high-efficiency organic light-emitting diodes (OLED) with 100% exciton harvesting. This review summarizes the recent development of electroluminescent Ir³⁺ complexes functionalized with host-featured carrier-transporting groups, with emphasis on correlations between functionalization, optoelectronic properties and device performance. According to the introducing approaches, the complexes were sorted with conjugated and aliphatic linkages, as well as the types of functional groups. The modification effect on physical properties and the state-of-the-art device performances were discussed.     

High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with fluorene core and blue fluorescence chromospheres

Two novel dendrimer-like blue-emitting dinuclear cyclometalated iridium (III) complexes, namely (DNaTPA)₂DBF(FIrpic)₂ and (DPyTPA)₂DBF(FIrpic)₂, have been successfully synthesized and characterized. In which FIrpic is an iridium (III) bis[(4,6-difluorophenyl)pyridinato-N,C2′]picolate blue-emitting phosphorescent chromophore core, DBF is a 2,7-diphenyl-9H-fluorene bridging core, DNaTPA and DPyTPA are deep blue-emitting fluorescent chromophores composed by rigid high-triplet-energy dendrons of triphenylamine-functionalized naphthalene or pyrene units, and the peripheral dendrons are connected with the ancillary ligand of the emitting core through nonconjugated ether linkage. Their photophysical, thermal, electrochemical, as well as electrophosphorescent properties were primarily studied. Both iridium (III) complexes exhibit high efficient blue emission in solution (38.5% and 19.2%) and a typical FIrpic emission in 1,3-bis(N-carbzolyl)benzene (mCP) matrix (27.0% and 24.1%). Simple bilayer phosphorescent organic light-emitting diodes (PHOLEDs) with a configuration of ITO/PEDOT:PSS/mCP:dopants/TmPyPB/Liq/Al achieved high efficiencies of 12.96 cd/A for current efficiency (CE), 6162 cd/m² for brightness, 6.22% for external quantum efficiency (EQE), and 3.13 lm/W for power efficiency (PE) with Commission International de L'Eclairage (CIE) coordinates of (0.19 ± 0.01, 0.35 ± 0.02) at only 2 wt% blend of (DNaTPA)₂DBF(FIrpic)₂. (DPyTPA)₂DBF(FIrpic)₂-doped devices also reach efficiencies of (9.14 cd/A, 7167 cd/m², 4.41%, 2.61 lm/W) at the same doping concentration. The results demonstrate that the introduction of dendritic blue-emitting fluorescent chromophore grafted into the blue phosphorescent chromosphere core through nonconjugated linkage is an efficient way to achieve high-efficiency sky-blue emission.     

High light electroluminescence of novel Cu(I) complexes

Three novel Cu(I) complexes, [CuDPEphos(NN)]BF₄, where NN=1-(4-5′-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (OXD-Pybm; L1) (1), 1-(4-carbazolylbutyl)-2-pyridinylbenzimidazole (Carl-Pybm; L2) (2), and 1-H-2-pyridinylbenzimidazole (HPybm; L3) (3), were synthesized. The photoluminescent (PL) properties of 1-3 and the electroluminescent (EL) properties of complexes 1 and 2 were systematically studied. The maximum brightness of 2-based devices was 8669 cd/m², which should be the best among the reported Cu(I) complexes-based devices.     

Synthesis and optoelectronic properties of a novel dinuclear cyclometalated platinum(II) complex containing triphenylamine-substituted indolo[3,2-b]carbazole derivative in the single-emissive-layer WPLEDs

A novel bi-picolinic acid derivative of H₂dipic-BTICz containing binary triphenylamine-substituted indolo[3,2-b]carbazole (BTICz) unit and its dinuclear platinum(II) complex of (dfppy)₂Pt₂(dipic-BTICz) were synthesized as a single-component emitter used in the white polymer light-emitting diodes (WPLEDs), where dfppy is 2-(2,4-difluorophenyl)pyridine and dipic-BTICz is an anion of H₂dipic-BTICz. The photophysical and electrochemical properties of (dfppy)₂Pt₂(dipic-BTICz) were investigated. Compared with the reported mononuclear platinum complex of (dfppy)Pt(pic), (dfppy)₂Pt₂(dipic-BTICz) exhibited a red-shifted photoluminescent peak at 434 nm in dilute dichloromethane (10⁻⁵ M), but a weakened and red-shifted aggregation emission peak at 640 nm besides its intrinsic emission at 445 nm in its neat films. Stable pure white emissions with CIE coordinates of (0.325±0.005, 0.345±0.015) and a maximum brightness of 208 cd/m² were observed in the (dfppy)₂Pt₂(dipic-BTICz)-doped single-emissive-layer (SEL) PLEDs using a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as a host matrix at 1 wt % dopant concentrations under applied voltages from 9 to 14 V. It indicates that the intrinsic and aggregation emissions of this dinuclear platinum complex were effectively tuned by inserting a new BTICz fluorophore in the dual picolinic acid derivative. Therefore, it is a promising single-component emitter to get white emission in SEL PLEDs.     

有机电致磷光材料的研究新进展

综述了近几年来应用于有机电致发光二极管的有机电致磷光材料的研究新进展,重点回顾了三原色小分子电致磷光材料的研究进展.     

High-efficient phosphorescent iridium(III) complexes with benzimidazole ligand for organic light-emitting diodes: Synthesis, electrochemistry and electroluminescent properties

Two phosphorescent complexes Ir(FFBI)₂(pmp) and Ir(FFBI)₂(pti) based on cyclometalated ligand 1-(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (FFBI) and ancillary ligands 2-(phenyliminomethyl)phenol (pmp) or 3-(pyridin-2-yl)-4,5,6,7-tetrahydro-2H-indazole (pti) were synthesized. The single crystal of Ir(FFBI)₂(pmp) was obtained. The light emitting and electrochemical properties of these complexes were studied. The electroluminescent devices based on these two complexes with the structure of ITO/NPB (40 nm)/Ir complex: CBP (30 nm)/BCP (15 nm)/Alq (30 nm)/LiF (1 nm)/Al (100 nm) emitted cyan color, with high brightness and efficiencies. The maximum external quantum efficiencies reached to 6.8% and 11.6%, respectively.     

Novel fluorene/carbazole hybrids with steric bulk as host materials for blue organic electrophosphorescent devices

The problem of self-quenching in organic electrophosphorescence devices has been extensively studied and partially solved by using sterically hindered spacers in phosphorescent dopants. This paper attempts to address this problem by using sterically hindered host materials. Novel fluorene/carbazole hybrids with tert-butyl substitutions, namely 9,9-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]fluorene (TBCPF) and 9,9-bis[4-(carbazol-9-yl)phenyl]-2,7-di-tert-butylfluorene (CPTBF), have been synthesized and characterized. The compounds exhibit not only high triplet energy (>2.8 eV), but also high glass transition temperature (>160 °C) and thermal stability. The substitution of inert tert-butyl groups to the carbazole/fluorene rings of these host molecules has a remarkable effect on the corresponding properties of the host materials, i.e. enhancing the thermal and electrochemical stability, weakening the intermolecular packing, and tuning the solid-state emission. Blue electrophosphorescent devices with enhanced performance were prepared by utilizing the sterically hindered host materials. The devices based on the four tert-butyl substituted material TBCPF exhibit unusual tolerance of high dopant concentration up to 20% and marked reduction of efficiency roll-off at higher current, indicating significant suppression of self-quenching effect in organic electrophosphorescent devices by the substitution of steric bulks.     

Synthesis and phosphorescent properties of two novel iridium (Ⅲ) complexes bearing bulky tert-butyl substituents

The synthesis and phosphorescence properties of two novel Ir(Ⅲ)complexes bearing tert-butyl substituents,bis(4-tert-butyl-2- phenylbenzothiozolato-N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tbt)_2Ir(acac)]and bis(4-tert-butyl-1-phenyl-1H-benzimidazolato- N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tpbi)_2Ir(acac)],are reported,their molecular structures are confirmed by~1H NMR,ESI-MS and elementary analysis.Photoluminescence(PL)studies revealed that they can emit strong green and orange phosphorescence in high quantum yields.Compared to their prototypes lacking of tert-butyl substituents,the two novel iridium(Ⅲ)complexes both have shorter lifetimes and improved or nearly similar PL quantum efficiencies,implying that the exciton quenching is inhibited effectively when molecular steric hindrance increases.The two chelates have great potential to be used as electrophosphorescent materials.