Huicai Ren

Highly Efficient Orange and White Organic Light-Emitting Diodes Based on New Orange Iridium Complexes

Highly Efficient Orange and White Organic Light-Emitting Diodes Based on New Orange Iridium Complexes

Deep-blue and white organic light-emitting diodes based on novel fluorene-cored derivatives with naphthylanthracene endcaps

Novel fluorene based deep-blue-emitting molecules with naphthylanthracene endcaps, namely 2,7-di(10-naphthylanthracene-9-yl)-9,9-dioctylfluorene (NAF1) and 7,7′-di(10-naphthylanthracene-9-yl)-9,9,9′,9′-tetraoctyl-2,2′-bifluorene (NAF2), are synthesized by a Suzuki cross-coupling reaction. These materials exhibit excellent thermal and amorphous stabilities, and high fluorescence quantum yield of over 70%. Organic light-emitting devices (OLEDs) using NAF1 or NAF2 as non-doped emitter exhibit bright deep blue electroluminescence with CIE coordinates of (0.15, 0.13) for NAF1, (0.16, 0.13) for NAF2. A maximum power efficiency of 2.2 lm W−1 (4.04 cd A−1, 4.04%) is achieved for NAF1, which is among the highest values ever reported for deep-blue fluorescent OLEDs. A further improved coordinates of (0.15, 0.09) with efficiencies of 3.56 cd A−1 and 2.10 lm W−1 are achieved for NAF1 upon tuning device thickness, which are also among the best data for non-doped deep blue fluorescent OLEDs with a CIE coordinate of y < 0.1. NAF1 serves as excellent host emitter when doped with an orange fluorophore (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, DCJTB). Upon careful tuning the doping level, the two-emitting-component (NAF1 : DCJTB) OLED realizes efficient white light emission with a power efficiency of 3.01 lm W−1 (7.66 cd A−1), a brightness of 12090 cd m−2, and a standard white light coordinates of (0.33, 0.33). This performance is among the best results ever reported for two-emitting-component white OLEDs based on fluorescent materials.

Homoleptic tris-cyclometalated iridium complexes with 2-phenylbenzothiazole ligands for highly efficient orange OLEDs

Homoleptic tris-cyclometalated iridium(III) complexes containing 2-phenylbenzothiazole derivatives as ligands have been successfully synthesized and characterized for the first time. Electron-donating (CH3, OCH3) and -withdrawing groups (F) were introduced into the 6-position of the benzothiazole moiety in the ligands to verify their influence on the optical and electronic properties of the complexes. Organic light-emitting diodes using these iridium complexes as doped emitters exhibited orange electrophosphorescence with excellent performances. An extremely high brightness of 95 800 cd m−2 and a maximum luminance efficiency of 87.9 cd A−1 (46.0 lm W−1) were achieved for the pristine complex without any substituent in the ligand. These performances represent a significant improvement for vacuum-deposited orange OLEDs and the new record of the efficiencies for orange OLEDs reported so far. The substituents in the ligand were observed to be rather unimportant to influence the performance of this series of iridium complexes.

Synthesis and Electrophosphorescence of Iridium Complexes Containing Benzothiazole-Based Ligands

Four heteroleptic bis-cyclometalated iridium(III) complexes containing 2-aryl-benzothiazole ligands, in which the aryl is dibenzofuran-2-yl [Ir(O-bt)2(acac)], dibenzothiophene-2-yl [Ir(S-bt)2(acac)], dibenzothiophene-S,S-dioxide-2-yl [Ir(SO2-bt)2(acac)] and 4-(diphenylphosphoryl)phenyl [Ir(PO-bt)2(acac)], have been synthesized and characterized for use in organic light-emitting diodes (OLEDs). These complexes emit bright yellow (551 nm) to orange-red (598 nm) phosphorescence at room temperature, the peak wavelengths of which can be finely tuned depending upon the electronic properties of the aryl group in the 2-position of benzothiazole. The strong electron-withdrawing aryls such as dibenzothiophene-S,S-dioxide2-yl and 4-(diphenylphosphoryl)phenyl caused bathochromatic shift of the iridium complex phosphorescence. These iridium complexes were used as doped emitters to fabricate yellow to orange-red OLEDs and good performance was obtained. In particular, a maximum luminance efficiency of 58.4 cd A(-1) (corresponding to 30.6 lm W(-1) and 19%) with CIE coordinates of (0.45, 0.52) was achieved for Ir(O-bt)2(acac)-based yellow device. Furthermore, the yellow emitting Ir(S-bt)2(acac) was used to fabricate two-element white OLED that exhibited a high efficiency of 32.4 cd A(-1) with CIE coordinates of (0.28, 0.44).

Solution-processible Thieno-[3,4-b]-pyrazine Derivatives with Large Stokes Shifts for Non-doped Red Light-emitting Diodes

A group of novel thieno-[3,4-b]-pyrazine-cored molecules containing polyphenyl dendrons with or without arylamino or carbazolyl surface groups (DTP, N-DTP and C-DTP) are synthesized and investigated. They are characterized by extra large Stokes shifts of over 250 nm. In addition, to provide the site-isolation effect on the planar emissive core, the bulky dendrons enable these molecules to be solution processible. The peripheral carbazolyl or arylamino units facilitate the hole transporting ability in the neat films of these molecules. These dendritic materials are used as a non-doped emitting layer to fabricate organic light-emitting diodes (OLEDs) using a spin coating technique and saturated red emission is obtained. The dendritic molecules with arylamino or carbazolyl surface groups (N-DTP and C-DTP) exhibit a brightness of 1020 cd m(-2) and a luminous efficiency of 0.6 cd A(-1) , both higher than the dendritic analog without the surface functional groups (DTP), even superior to the small molecular reference compound which fails to transmit pure red emission under identical conditions. This performance is also comparable with that from vacuum deposited thieno-[3,4-b]-pyrazine-based counterparts and that for some other solution processible red fluorescent dendrimers. This is the first example of solution processible thieno-[3,4-b]-pyrazine derivatives for OLED applications.

Dicyanopyrazine-Containing Fused Aromatic Molecules: Potential n-Type Materials for Use in Optoelectronic Devices

Abstract Two dicyanopyrazine-containing aromatic compounds, pyrazino[2′,3′:9,10]phenanthro[4,5-fgh]quinoxaline-5,6,12,13-tetracarbonitrile (PPQD) and pyrazino[2′,3′:9,10]phenanthro[4,5-fgh]quinoxaline-5,6,12,13-tetracarbonitrile,2,9-bis(1,1-dimethylethyl) (PPQB), which have remarkably high electron affinity and ionization potential, were synthesized and qualified as potential n-type materials for use in solar cells and organic light-emitting diodes.

SYNTHESIS AND CHARACTERIZATION OF NOVEL PERYLENEDIIMIDE-CORED DENDRIMER WITH FLUORINATED SHELL

A perylenediimide-based dendrimer, PDI-F, was designed and synthesized for application as red host emitter in nondoped organic light-emitting diodes. PDI-F was designed with perylenediimide as the luminescence core and pentafluorophenyl rings as the surface groups. The dendrimer molecule constructed in this way is bulky and nonplanar. PDI-F exhibits good solubility in common organic solvents and is suitable for wet methods such as spin coating to make thin films. All new compounds of the intermediates and the target dendrimer were characterized by 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. In addition, the ultraviolet (UV) absorption and fluorescence (FL) of PDI-F were measured and discussed. To the best of our knowledge, this is the first report of dendrimer PDI-F.