Chen-Han Chien

Switching On Luminescence by the Self-Assembly of a Platinum(II) Complex into Gelating Nanofibers and Electroluminescent Films†

Triplet emitters based on platinum(II) complexes have gained major attention in recent times. They can form aggregates or excimers, causing shifts in the emitted wavelengths and affecting the photoluminescence quantum yields (PLQYs). Even though this effect can be exploited for the construction of white organic light emitting diodes (WOLEDs), it is disadvantageous for applications where color purity is desirable. Terpyridine ligands and their N^C^N and N^N^C analogues have been coordinated to platinum(II), leading to neutral, mono-, or doubly charged species, some of which display bright luminescence. They can form supramolecular structures, such as nanowires, nanosheets, and polymeric mesophases, with interesting optical properties. For low-molecular-weight organoor hydrogelators, the operating mechanism of gelation has been recognized as a supramolecular effect, where the constituting fibers, usually of microscale lengths and nanoscale diameters, are formed in solution predominantly by unidirectional self-assembly. The entanglement of filaments gives a network that entraps solvent molecules within the compartments. As supramolecular gels provide fibrous aggregates with long-range order, they could be of interest in the fields of optoelectronic devices and sensors. In this context, organometallic gelators can display metal–metal interactions that influence their properties. Herein we present a straightforward one-pot synthesis of neutral, soluble platinum(II) coordination compounds bearing a dianionic tridentate terpyridine-like ligand. The coordination of an alkyl pyridine ancillary moiety to the 2,6bis(tetrazolyl)pyridine complex allowed us to enhance the solubility and thus the processability. The synthetic approach involved mild reaction conditions that involved a nonnucleophilic base and an adequate inorganic platinum(II) precursor. Moistureand oxygen exclusion were not required, and the product was easily purified by repeated precipitation (Scheme 1). The emission intensity of the complex attained a

Iridium(III) Emitters Based on 1,4-Disubstituted-1H-1,2,3-triazoles as Cyclometalating Ligand: Synthesis, Characterization, and Electroluminescent Devices

A series of blue and blue-green emitters based on neutral bis- and tris-cyclometalated Ir(III) complexes with 1-benzyl-4-(2,6-difluorophenyl)-1H-1,2,3-triazole (dfptrBn) as cyclometalating ligand is reported. The bis-cyclometalated complexes of the type [Ir(dfptrBn)(2)(L(^)X)] with different ancillary ligands, L(^)X = picolinate (pic) (2) or 2-(5-(perfluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine (pytrF(5)) (3), are described and their photophysical properties compared with the analogous complexes containing the archetypal 2-(2,4-difluorophenyl)pyridinato (dfppy) as cyclometaled ligand (C(^)N). Complex 2 exhibits a marked solvatochromic behavior, from 475 nm in toluene to 534 nm in formamide, due to the strong MLCT character of its emissive excited state. Complex 3 displays a true-blue emission, narrower in the visible part than FIrpic. In addition, the homoleptic complex [Ir(dfprBn)(3)] (4) and the heteroleptic compounds with mixed arylpyridine/aryltriazole ligands, [Ir(dfptrBn)(2)(C(^)N)] (C(^)N = 2-phenylpyridinato (ppy) (5) or dfppy (6)), have been synthesized and fully characterized. The facial (fac) complex fac-4 is emissive at 77 K showing a deep-blue emission, but it is not luminescent in solution at room temperature similarly to their phenylpyrazole counterparts. However, the fac isomers, fac-5 and fac-6, are highly emissive in solution and thin films, reaching emission quantum yields of 76%, with emission colors in the blue to blue-green region. The photophysical properties for all complexes have been rationalized by means of quantum-chemical calculations. In addition, we constructed electroluminescent devices, organic light-emitting diodes (OLEDs) by sublimation of fac-6, and by solution processed polymer-based devices (PLEDs) using complexes fac-5 or fac-6 as dopants.

Highly efficient red electrophosphorescent devices based on an iridium complex with trifluoromethyl-substituted pyrimidine ligand

Highly efficient red-emitting electrophosphorescent devices were fabricated by doping an iridium (Ir) complex containing trifluoromethyl (CF3)-substituted pyrimidine ligand into a conjugated bipolar polyfluorene with triphenylamine and oxadiazole as side chains. The device efficiency can be enhanced through effective exciton confinement using a layer of 1,3,5-tris(N- phenylbenzimidazol-2-yl)benzene on the cathode side and a layer of in situ polymerized tetraphenyldiamine-perfluorocyclobutane on the anode side. For a blend with 5wt% of the Ir complex, a maximum external quantum efficiency of 7.9 photon/electron % and a maximum brightness of 15800cd∕m2 are reached with Commission Internationale de L’Eclairage chromaticity coordinates of x=0.65 and y=0.34.

Highly efficient red electrophosphorescent device incorporating a bipolar triphenylamine/bisphenylsulfonyl-substituted fluorene hybrid as the host

We have fabricated highly efficient red phosphorescent organic light-emitting diodes (PHOLEDs) incorporating a bipolar host material, 2,7-bis(phenylsulfonyl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (SAF), doped with 7 wt% tris(1-phenylisoquinolinolato-C2,N)iridium(III) [Ir(piq)3]. Attaching the electron-donating (p-type) triphenylamine group onto the electron-accepting (n-type) 2,7-bis(phenylsulfonyl)fluorene segment (through the C9 position of the fluorene unit) imparts SAF with good morphological stability, high triplet energy gap (ET), bipolar transporting ability, and matching energy levels with adjacent carrier-transporting layers. Consequently, the SAF-based red-PHOLED exhibited a very low turn-on voltage (2.4 V) and high electroluminescence efficiencies of 15.8% and 22.0 lm W−1, superior to those of the corresponding device incorporating a conventional host material, 4,4′-N,N′-dicarbazolbiphenyl (CBP; 3.2 V, 8.5%, and 8.4 lm W−1, respectively). At a practical brightness of 1000 cd m−2, the efficiencies of the SAF-based red-PHOLED remained high (13.1%, 14.4 lm W−1).

A solution-processable bipolar molecular glass as a host material for white electrophosphorescent devices

A solution-processable bipolar material tBu-OXDTFA comprising an electron-rich triphenylamine core and electron-deficient oxadiazole/fluorene peripheries was synthesized. This dendrimer-like molecule not only possesses a high triplet energy (2.74 eV) but also exhibits excellent film-forming properties upon solution processing. We achieved highly efficient white electrophosphorescent OLEDs (22.3 cd A−1, 11.6%) through solution processing, wherein the single white emitting layer was readily formed after spin-coating a solution of blue- and red-phosphor co-dopants containing tBu-OXDTFA as the host matrix.

Syntheses, photophysics, and application of iridium(III) phosphorescent emitters for highly efficient, long-life organic light-emitting diodes.

Rational design and synthesis of Ir(III) complexes (1-3) bearing two cyclometalated ligands (C--N) and one 2-(diphenylphosphino)phenolate chelate (P--O) as well as the corresponding Ir(III) derivatives (4-6) with only one (C--N) ligand and two P--O chelates are reported, where (C--NH)=phenylpyridine (ppyH), 1-phenylisoquinoline (piqH), and 4-phenylquinazoline (nazoH). Single crystal X-ray diffraction studies of 3 reveal a distorted octahedral coordination geometry, in which two nazo ligands adopt an eclipsed configuration, with the third P--O ligand located trans to the phenyl group of both nazo ligands, confirming the general skeletal pattern for 1-3. In sharp contrast, complex 4 reveals a trans-disposition for the PPh2 groups, along with the phenolate groups residing opposite the unique cyclometalated ppy ligand, which is the representative structure for 4-6. These Ir(III) complexes exhibit green-to-red photoluminescence with moderate to high quantum efficiencies in the degassed fluid state and bright emission in the solid state. For 1-6, the resolved emission spectroscopy and relaxation dynamics are well rationalized by the computational approach. OLEDs fabricated using 12 wt. % of 3 doped in CBP and with BCP as hole blocking material, give bright electroluminescence with lambda(max)=628 nm and CIE(xy) coordinates (0.65, 0.34). The turn-on voltage is 3.2 V, while the current efficiency and the power efficiency reach 11.2 cd A(-1) and 4.5 lm W(-1) at 20 mA cm(-2). The maximum efficiency reaches 14.7 cd A(-1)and 6.8 lm W(-1) upon switching to TPBI as hole blocking material. For evaluating device lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and BAlq as hole blocking material, shows a remarkably long lifetime up to 36,000 h at an initial luminance of 500 cd m(-2).

Mechanism of nitrogen coimplant for suppressing boron penetration in p+‐polycrystalline silicon gate of p metal–oxide semiconductor field effect transistor

The mechanism of the nitrogen co‐implant to suppress the boron penetration in p+‐polycrystalline silicon gate has been investigated. The nitrogen coimplant with the BF+2 combines with the boron to form a B–N complex which results in a retardation of boron diffusion. It is found that metal–oxide–silicon capacitors with nitrogen implantation show improved electrical properties.

Temperature-accelerated dielectric breakdown in ultrathin gate oxides

Temperature-accelerated effects on dielectric breakdown of ultrathin gate oxide with thickness ranging from 8.7 to 2.5 nm are investigated and analyzed. Although superior reliability for ultrathin gate oxide at room temperature has been reported in recent literatures, a strong temperature-accelerated degradation of oxide reliability is observed in this study. Experimental results show that both charge-to-breakdown (Qbd) and breakdown field (Ebd) characteristics are greatly aggravated for ultrathin oxide at elevated temperature. The Arrhenius plot also confirms that the activation energies of Qbd and Ebd increase significantly as oxide thickness decreases, explaining the higher sensitivity to temperature for thinner oxides.

Suppression of Boron Penetration in P+-Poly-Si Gate Metal-Oxide-Semiconductor Transistor Using Nitrogen Implantation

The mechanism and the optimization of nitrogen implantation for suppression the boron penetration in p + -poly-Si gate metal-oxide-semiconductor capacitor is reported. This nitrogen co-implantation process exhibits a good suppression of boron penetration and a better electrical characteristic than that of control sample. It was found that nitrogen combines with the boron to form a B-N complex, retarding the penetration of boron itself, was identified by XPS measurements. The optimum nitrogen dosage is also found in this study.

Studies on damage removing efficiency of B11+ and BF+2 implanted Si0.84Ge0.16 epilayers by rapid thermal annealing

High quality metastable pseudomorphic Si1−xGex epilayers were grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4. These epilayers were implanted with 40 keV B11+ and 100 keV BF+2 ions at a dose of 1×1015 ions/cm2 and then annealed by rapid thermal annealing (RTA) processes at temperatures of 600, 650, 700, and 750 °C for 30 s duration. Double‐crystal x‐ray diffractometry was used to evaluate the level of the implant‐induced damage and the damage removing efficiency of both ion implanted samples at different RTA conditions. The results show that the RTA process is more effective at removing damage from B11+ implanted samples than from those implanted with BF+2.