Homoleptic Structures Research Articles

Combinatorial Coordination Self-Assembly for Organopalladium Cages with Fine-Tuned Structure and Function.

Discrete organopalladium coordination cages have shown great potential in applications ranging from molecular recognition and sensing, drug delivery to enzymatic catalysis. While many of the known organopalladium cages are homoleptic structures with regular polyhedral shapes and symmetric inner cavities, heteroleptic cages with complex architectures and new functions coming from their anisotropic cavities have received an increasing attention recently. In this concept article, we discuss a powerful combinatorial coordination self-assembly strategy toward the construction of a family of organopalladium cages, including both homoleptic and heteroleptic ones, from a given library of ligands. Within such a cage family, the heteroleptic cages often feature systematically fine-tuned structures and emergent properties, distinct from their parent homoleptic counterparts. We hope the concepts and examples provided in this article can offer some rational guidance for the design of new coordination cages toward advanced functions.

Atomic layer deposition of Y2O3 films using a novel liquid homoleptic yttrium precursor tris(sec-butylcyclopentadienyl)yttrium [Y(sBuCp)3] and water.

Atomic layer deposition (ALD) of Y2O3 thin films was studied using a novel homoleptic yttrium ALD precursor: tris(sec-butylcyclopentadienyl)yttrium [Y(sBuCp)3]. Y(sBuCp)3 is a liquid at room temperature. The thermogravimetry curve for Y(sBuCp)3 is clean, with no indication of decomposition or residue formation. Thermogravimetry-differential thermal analysis measurements showed that Y(sBuCp)3 is stable for 18 weeks at 190 °C. Y(sBuCp)3 has a homoleptic structure. Thus, a reduction in manufacturing costs is expected compared to those associated with heteroleptic precursors because additional chemical synthesis steps are usually necessary to produce heteroleptic compounds. In addition, ALD of Y2O3 was demonstrated using Y(sBuCp)3 and water as a co-reactant. The deposition temperature was varied from 200 to 350 °C. The growth rate was 1.7 Å per cycle. In addition, neither carbon nor nitrogen contamination was detected in the Y2O3 films by X-ray photoelectron spectroscopy. Furthermore, smooth films were confirmed by X-ray secondary-electron microscopy. The root-mean-square roughness was measured to be 0.660 nm by atomic force microscopy. Metal-insulator-semiconductor (MIS) Pt/Y2O3/p-Si devices were fabricated to evaluate the electrical properties of the Y2O3 films. An electric breakdown field of -6.5 MV cm-1 and a leakage current density of ∼3.2 × 10-3 A cm-2 at 1 MV cm-1 were determined. The permittivity of Y2O3 was estimated to be 11.5 at 100 kHz. Therefore, compared with conventional solid precursors, Y(sBuCp)3 is suitable for use in ALD manufacturing processes.

Color tuning of iridium(III) complexes containing 2-phenylbenzothiazole-based cyclometalated ligands for application in highly efficient organic light-emitting diodes

By introducing a carbazolyl or diphenylamino substituent into the cyclometalated ligand, replacing the ancillary ligand of acetylacetone into 2-picolinic acid, or employing a homoleptic molecular structure, six complexes (TM1~6) bearing a similar molecular skeleton of yellow-emissive bis(2-phenylbenzo[d]thiozolato-N,C2')iridium (III) (acetylacetonate) (Ir-bt) have been acquired. In despite of their different types of ancillary ligand, or different homoleptic or heteroleptic molecular structures, TM1~3 bearing carbazolyl-modified cyclometalated ligands all emit yellow photoluminescence (PL) with their PL maximum (λPLmax) locating at 555–565 nm. Nevertheless, for TM4~6 bearing diphenylamino-modified cyclometalated ligands, they show red PL emission whose λPLmax = 618–636 nm, which is significantly red-shifted than that of Ir-bt. Note that the PL emission of these diphenylamino-modified iridium chelates can be fine-tuned by alteration on its ancillary ligand, or using a homoleptic structure. By taking advantage of the excellent thermal stability and relatively high PL efficiencies of TM3 and TM6, organic light-emitting diodes devices (OLEDs) using them as phosphorescent guests show relatively high electroluminescence performance. The TM3-based device can emit highly efficient yellow light with CIE coordinates of (0.43, 0.56), a maximum current efficiency (ηLmax) of 54.2 cd·A−1, and a maximum power efficiency (ηPmax) of 48.9 lm·W−1, which is one of the highest reported power efficiency data of yellow PhOLEDs; the TM6-based device can emit orange emission with CIE coordinates of (0.57, 0.42), ηLmax of 18.6 cd·A−1, and ηPmax of 14.3 lm·W−1.

Preferential Orientation of Tetrahedral Silicon-Based Hosts in Phosphorescent Organic Light-Emitting Diodes.

Vacuum-processed diphenylbis(3-(pyridine-2-yl)phenyl)silane (2PTPS), diphenylbis(3-(pyridine-3-yl)phenyl)silane (3PTPS), and diphenylbis(3-(pyridine-4-yl)phenyl)silane (4PTPS) have been used as electron-transporting host materials combined with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the hole-transporting host, which induce balanced charge carrier transport for high-efficiency phosphorescent organic light-emitting diodes. The 4PTPS-based organic light-emitting diodes with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant showed highest current efficiency and external quantum efficiency of 53.54 cd/A and 15.61%, compared to 2PTPS (40.75 cd/A, 11.84%) and 3PTPS (29.35 cd/A, 8.54%). These results were attributed to the well-aligned structure with preferential horizontal orientation of the emitting material layer by the diffraction intensity distribution as a function of azimuthal angle in two-dimensional grazing incidence X-ray diffraction analysis. The molecular orientation of TCTA:4PTPS material with a narrow azimuthal intensity distribution had better priority to the horizontal direction than the other TCTA:2PTPS and TCTA:3PTPS materials, which is related to the charge transport as well as the device efficiency. We found that the preferential horizontal orientation of the co-host material with a balanced charge carrier was not affected by Ir(ppy)3 dopant with a homoleptic structure and bis-[2-(4,6-difluorophenyl)pyridinato-N,C2](picolinato)iridium [Firpic] dopant with a heteroleptic structure in the co-host/dopant system.