Light-emitting Dopant Research Articles

Cyclometalated platinum(II) complexes with acyclic diaminocarbene ligands for OLED application.

A novel series of cyclometalated platinum(II) complexes bearing acyclic diaminocarbene (ADC) ancillary ligands were designed and prepared. Their photophysical properties were systematically studied through experimental and theoretical investigations. All complexes exhibit green phosphorescence with a quantum efficiency of up to 45% in 2 wt% doped PMMA film at room temperature. The complexes are used as light-emitting dopants for organic light-emitting diode (OLED) fabrication. The devices displayed a green emission with a maximum current efficiency of 2.9 cd A-1 and a luminance of 2700 cd m-2. These results show that these cyclometalated platinum(II) complexes can be used as efficient green emitting components of OLED devices.

Deep Blue Phosphorescence from Platinum Complexes Featuring Cyclometalated N-Pyridyl Carbazole Ligands with Monocarborane Clusters (CB11H12-).

The utilization of deep blue phosphorescent materials in high-performance displays and solid-state lighting requires high quantum efficiencies and color purities. Here, we describe the preparation and luminescent properties of novel platinum triplet emitters featuring cyclometalated N-pyridyl-carbazole ligands functionalized with closo-monocarborane clusters [CB11H12]-. All reported complexes were fully characterized by using standard small molecule techniques (UV-vis, cyclic voltammetry, nuclear magnetic resonance (NMR), high-resolution mass spectrometry (HRMS)), and their solid-state structures were elucidated by X-ray diffraction. These platinum phosphors emit in the blue region of the visible wavelength spectrum in both the solid and solution states. Complex 4a exhibits the highest luminous efficiency at λem = 439 nm with a photoluminescent quantum yield (PLQY) of 60% by dispersing in a PMMA matrix. Electrochemical and computational studies of complexes 4a and 4b revealed that the blue phosphorescence originates mainly from intraligand 3π → π* (3ILCT) transitions with relatively small 3MLCT mixing. A deep-blue OLED containing 4a as the light-emitting dopant was successfully fabricated using a solution-processed method, and the device exhibited blue photoluminescence with CIE coordinates of (0.17, 0.15) and a maximum external quantum efficiency (EQEmax) value of 6.2%. This article represents the pioneering study of a deep blue PhOLED using a Pt complex bearing a closo-monocarborane anion substituent, providing a new avenue into the preparation of novel triplet emitters based on boron-rich cluster anions.

A novel H-bonding self-assembly heteromeric molecular duplex bearing host and guest energy transfer units as high-performance electroluminescent material

Two oligoamide strands with complementary H-bonding sequences bearing 4HB-NIM and 4HB-CzNI were synthesized. 4HB-NIM and 4HB-CzNI could be self-assembled into a heterodimeric dyad (namely 4HB-NIM-CzNI)via quadruple H-bond interactions. Photoluminescence measurements revealed that in both dilute solution and doped film states, more efficient host-guest energy transfer processes could be observed in the duplex 4HB-NIM-CzNI than the physical blends of the small molecular guest reference compound NIM and the host single strand 4HB-CzNI, which should be attributed to the shortened spatial distances in 4HB-NIM-CzNI. In addition, in comparison with NIM and the guest single strand 4HB-NIM, 4HB-NIM-CzNI shows much higher photoluminescence quantum yield [0.53 vs 0.04 (NIM) or 0.35 (4HB-NIM)] in neat-film state, indicative of the more alleviated concentration quenching of the guest fluorophore in 4HB-NIM-CzNI than 4HB-NIM and NIM. As a consequence, an organic light-emitting diode (OLED) with 4HB-NIM-CzNI as the light-emitting dopant shows much more improved electroluminescent performance than its 4HB-NIM-based reference OLED: with lower turn-on voltage (5.0 vs 5.9 V), higher maximum luminance (5260 vs 2980 cd m−2) and current efficiency (3.5 vs 3.0 cd A−1) as well as lower efficiency roll-off. All these results indicated that the integration of both host and guest fluorophores into H-bonding self-assembled material should be an effective strategy to construct high performance supramolecular electroluminescent materials.

A molecular thermometer based on luminescence of copper(II) tetraphenylporphyrin

The photoluminescence (PL) spectra from solid samples consisting of polystyrene and 5,10,15,20-tetraphenyl-21H,23H-porphine copper(II) (CuTPP) revealed two sharp peaks at 653 and 720 nm, and indicated another broad peak at around 780 nm, which could not be observed in CuTPP solutions. The intensity ratio of the two peaks appearing at 653 nm and at around 780 nm demonstrated clear dependence on temperature. This dependence of the PL intensity ratio was observed under the atmosphere and even in water. The findings mean that we were able to utilize PL from CuTPP as a thermometer under various conditions. We measured the temperatures of an organic light-emitting diode (OLED) during operation based on its electroluminescence, where the OLED contained CuTPP as a light-emitting dopant, to demonstrate the CuTPP thermometer.

Color tuning of red phosphorescence: New iridium complexes containing fluorinated 2,3-diphenylquinoxaline ligands

The new iridium complexes containing a derivative of 2,3-diphenylquinoxaline as an emitting ligand were synthesized, and their photophysical properties were investigated. The complexes prepared in this study were bis(6-F-2,3-di(p-fluorophenyl) quinoxalinato)iridium acetylacetonate (Ir(6-F-2,3-dpqx-F 2) 2(acac)) and bis(6-F-2,3-di(p-fluorophenyl)quinoxalinato)iridium pyrazolonates (Ir(6-F-2,3-dpqx-F 2) 2(przl1) and Ir(6-F-2,3-dpqx-F 2) 2(przl2)). Their photoluminescence maxima appeared at 638, 632 and 630 nm, respectively. The electroluminescence study revealed that the CIE coordinates of the devices containing Ir(6-F-2,3-dpqx-F 2) 2(acac) and Ir(6-F-2,3-dpqx-F 2) 2(przl2) as a light-emitting dopant were (0.675, 0.313) and (0.685, 0.310), respectively, very close to those of the saturated standard red emission.

Blue light-emitting devices based on 1,8-acridinedione derivatives

Two small non-aromatic organic molecules, 1,2,3,4,5,6,7,8,9,10-decahydro-1,8-acridinedione (DAD) and 3,3,6,6-tetramethyl-1,2,3,4,5,6,7,8,9,10-decahydro-1,8-acridinedione (TDAD) were synthesized and used as blue light-emitting dopants in organic electroluminescent devices. A general device structure, ITO/NPB (20 nm)/CBP (20 nm)/DAD:TPBI ( X%, Y nm)/TPBI ( Z nm)/Mg:Ag (10:1; 55 nm)/Ag (100 nm) was employed for this study, where NPB, CBP and TPBI stand for 4,4′-bis[ N-(1-naphthyl)- N-phenyl-amino]-biphenyl, 4,4′-dicarbazolyl-1,1′-biphenyl and 2,2′,2″-(1,3,5-phenylene)tris-[1-phenyl-1 H-benzimidazole], respectively. Efficient blue emission with excellent Commission Internationale de L’Eclairage (CIE) coordinates ( X=0.15, Y=0.08) and maximum luminance >1000 cd/m 2 were obtained from the devices. The performances of the devices depend greatly on the dopant concentration and thickness of the emitting layer.

Circularly polarized light generated by photoexcitation of luminophores in glassy liquid-crystal films

Optical information processing, display and storage can be accomplished with linearly or circularly polarized light. In passive (non-emitting) devices, linear polarization can be produced by anisotropic absorption of light1, whereas circular polarization has been attained by selective reflection of unpolarized light propagating through a chiral-nematic liquid-crystal film2. Active (light-emitting) devices capable of polarized emission are also needed. In principle, optical and electronic excitation of materials containing uniaxially and helically arranged luminophores should produce linearly and circularly polarized emission, respectively. In practice, the former is easier to achieve and is therefore more technologically advanced3,4,5,6,7,8. Here we report the generation of strongly circularly polarized photoluminescence from films of glass-forming chiral-nematic liquid crystals9 in which are embedded light-emitting dopants. This host material apparently induced alignment of the luminophores to a degree that produces almost pure circular polarization within the 400–420-nm wavelength band of the emitted light. We anticipate that composite films of this sort might find applications within photonic technology such as colour-image projection10 and stereoscopic displays11.