Phosphorescent Pt(II) and Pd(II) Complexes for Efficient,High‐Color‐Quality,and Stable OLEDs

Phosphorescent organic light‐emitting diodes (OLEDs) are leading candidates for next‐generation displays and solid‐state lighting technologies. Much of the academic and commercial pursuits in phosphorescent OLEDs have been dominated by Ir(III) complexes. Over the past decade recent developments have enabled square planar Pt(II) and Pd(II) complexes to meet or exceed the performance of Ir complexes in many aspects. In particular, the development of N‐heterocyclic carbene‐based emitters and tetradentate cyclometalated Pt and Pd complexes have significantly improved the emission efficiency and reduced their radiative lifetimes making them competitive with the best reported Ir complexes. Furthermore, their unique and diverse molecular design possibilities have enabled exciting photophysical attributes including narrower emission spectra, excimer ‐based white emission, and thermally activated delayed fluorescence. These developments have enabled the fabrication of efficient and “pure” blue OLEDs, single‐doped white devices with EQEs of over 25% and high CRI, and device operational lifetimes which show early promise that square planar metal complexes can be stable enough for commercialization. These accomplishments have brought Pt complexes to the forefront of academic research. The molecular design strategies, photophysical characteristics, and device performance resulting from the major advancements in emissive Pt and Pd square planar complexes are discussed.     

Synthesis of fluorescent dendrimers with an oligo(phenylenevinylene) core

Novel fluorescent dendrimers of first, second, and third generation bearing a conjugated oligo(phenylenevinylene) (OPV) core and peripherial allyl chains as dendrons have been synthesized by a convergent method. The compounds have been fully characterized by 1H, 13C NMR, FTIR, UV-vis, and fluorescence spectroscopy, MALDI-TOF or FAB+ mass spectroscopy and elemental analysis. All dendrimers showed in solution a blue fluorescence with a maximum wavelength at 444-446 nm and can be deposited as thin films emitting in the blue-green region. The most homogeneous films were obtained for the second generation dendrimer which also exhibits the higher quantum yield in solution. These properties make it a possible candidate for application in organic light emitting diodes (OLEDs).     

Synthesis, characterization, and electrochemical properties of mono-, di-, and trinuclear transition Metal [60]fullerene complexes containing diphosphine cis-Ph2PCH=CHPPh2 ligand

New transition metal fullerene complexes containing cis-Ph2PCH=CHPPh2 (dppet) ligand have been investigated. The mononuclear complexes (etau2-C60)M(cis-dppet) (1, 2; M = Pd, Pt) were prepared by reaction of C60 with M(dba)2 (dba = dibenzylideneacetone) followed by treatment with cis-dppet, while the in situ prepared 1 and 2 reacted with M1(PPh3)4 to afford dinuclear complexes (eta2 : eta2-C60)M(cis-dppet)M1 (PPh3)2 (3-6; M, M1 = Pd, Pt). Similarly, trinuclear complexes (eta2 : eta2-C60) M(cis-dppet)M1 (dppr) (7-10; M, M1 = Pd, Pt; dppr = (eta5-Ph2PC5H4)2Ru) could be synthesized by reaction of the in situ prepared 3-6 with dppr. 1-10 were characterized by elemental analysis and spectroscopy. Cyclic voltammetric studies on 2 (M = Pt), 3 (M = Pd, M1 = Pd) and 9 (M = Pt, M1 = Pd) provided further evidence for the eta2-coordination of C60 to one metal fragment or two metal fragments in these complexes.     

MALDI TOF mass spectrometry for the characterization of phosphorus-containing dendrimers. Scope and limitations

Neutral phosphorus-containing dendrimers with aldehyde groups at the periphery have been analyzed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) up to generation four. Although the expected quasi-molecular ion is generally observed, the mass spectral pattern, presence of fragments and adducts related to the original skeleton, is highly relevant to the sample preparation (nature of the matrix: 2-5-dihydroxybenzoic acid (2.5-DHB), 1,8-dihydroxy-9[10H]-anthracenone (dithranol), 6-azathiothymine, 2,4,6-trihydroxyacetophenon, 7-hydroxycoumarin or 2-anthramine, and addition of alkali metal salts). The dithranol matrix with addition of LiI offers milder conditions; however, abundant fragments are still observed for the higher generation dendrimers. Investigation of these effects in connection with SEC, NMR, and MALDI-TOFMS studies of UV preirradiated dendrimers allows the assumption to be made that fragmentation occurs in MALDI due to the relatively strong absorption of the dendrimers at 337 nm. Fragmentations and formation of adducts involve nitrogen-nitrogen bond cleavage, imine metathesis, and reaction of aldehyde groups with internal imino groups.     

Novel thieno-[3,4-b]-pyrazines cored dendrimers with carbazole dendrons: design, synthesis, and application in solution-processed red organic light-emitting diodes

A series of novel red-emitting thieno-[3,4-b]-pyrazine-cored molecules containing oligo-carbazole dendrons (called C1-TP, C2-TP) are synthesized. Their photophysical, electrochemical, and electroluminescent properties are investigated. The peripheral carbazolyl units facilitate the hole transporting ability and inhibit the intermolecular interactions, but quench the fluorescence of the thieno-[3,4-b]-pyrazine core through Intramolecular Charge Transfer (ICT). Introduction of a polyphenyl spacer between the core and the first generation carbazole dendrons, i.e., C-DTP, decreases the ICT efficiency. In addition to providing the site-isolation effect on the planar emissive core, these bulky dendrons enable these molecules to be solution processable. As a result, efficient OLEDs with saturated red emission are fabricated by spin coating technique using these dendritic materials as nondoped emitting layer. C-DTP exhibits much better device performance than C1-TP and C2-TP, while the small molecular reference compound containing neither the spacer nor the carbazole dendrons (TP) fails to transmit pure red emission under identical conditions. A brightness of 925 cd m(-2) and a luminous efficiency of 0.53 cd A(-1) are obtained for C-DTP, which are comparable with OLEDs fabricated from thieno-[3,4-b]-pyrazine-based counterparts by the vacuum deposition method or those assembled with other red fluorescent dendrimers via the solution processing method.     

Highly fluorescent dendrimers containing stilbene, and 4-styrylstilbene with resorcinarene cores: synthesis and optical properties

Dendron conjugated branches of stilbene and 4-styrylstilbene groups have been attached to resor-cinarene cores. A noticeable effect in solution for all dendrimers was observed in the fluorescence quantum yield. The optical properties do not change with concentration in solution. The optical properties of thin films are identical to those of the solutions indicating the absence of intermolecular interactions. The dendrimers were characterized by 1H, 13C NMR, FTIR, UV-Vis, fluorescence spectroscopy, MALDI-TOF or FAB+ mass spectrometry, and elemental analysis.     

Dendritic functionalization of monolayer-protected gold nanoparticles

This paper describes the facile synthesis of nanoparticle-cored dendrimers (NCDs) and nanoparticle megamers from monolayer-protected gold clusters using either single or multi-step reactions. First, 11-mercaptoundecanoic acid/hexanethiolate-protected gold clusters were synthesized using the Schiffrin reaction followed by the ligand place-exchange reaction. A convergent approach for the synthesis of nanoparticle-cored dendrimers uses a single step reaction that is an ester coupling reaction of hydroxy-functionalized dendrons with carboxylic acid-functionalized gold clusters. A divergent approach, which is based on multi-step reactions, employs the repetition of an amide coupling reaction and a Michael addition reaction to build polyamidoamine dendritic architectures around a nanoparticle core. Nanoparticle megamers, which are large dendrimer-induced nanoparticle aggregates with an average diameter of more than 300 nm, were prepared by the amide coupling reaction between polyamiodoamine [G-2] dendrimers and carboxylic acid-functionalized gold clusters. ¹H NMR spectroscopy, FT-IR spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) were used for the characterization of these hybrid nanoparticles.     

Chemical vapor generation of arsane in the presence of L-cysteine. Mechanistic studies and their analytical feedback

The complex reactivity of the system As-AH-RSH-THB (As=As(III), As(V); AH=HCl, HClO4, CH3COOH; RSH=L-cysteine (Cys); THB=NaBH4) was investigated using continuous flow (CF) hydride generation (HG) coupled either with atomic absorption (AAS) or atomic fluorescence spectrometry (AFS). AsH3 generation was examined in the presence of Cys by varying acidity and the type of acid, the mixing sequence, and the reaction time of reagents. The strong depression of arsane generation, which is typically observed in the range of acidity of 0.2-2 M HCl, can be addressed to the low reaction rate of thiol-borane, hydroboron complexes, or both toward those As(III) substrates that are formed in the same reaction environment. The simultaneous presence of Cys-borane and As(III)-Cys species is at the origin of the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. The selective formation of Cys-borane complexes, which are formed faster than As(III)-thiol complexes, can be achieved by a careful choice of the mixing sequence of the reagents. The simultaneous mixing of sample, Cys, and THB is able to reduce substantially the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. These properties were employed to implement a simple method for selective determination of As(III) in samples containing inorganic arsenic: (i) Total inorganic arsenic is determined by sample treatment with 0.2 M Cys for 30 min, acidity 0.1 M HCl, followed by CF-HG-AFS; (ii) As(III) is selectively determined in 0.005 M CH3COOH in the presence of Cys using a chemifold setup allowing the simultaneous mixing of sample, 0.2 M Cys and 0.1 M THB. The selectivity, measured from the ratio between the slopes of calibration graphs As(III)/As(V), is 220. The interference effects of Cu(II), Fe(III), Ni(II), Co(II), Ag(I), Pd(II), and Pt(IV) can be kept under control using the simultaneous mixing of all the reagents. The tolerance toward the interferences was almost the same as that obtained by allowing the formation of As(III)-Cys complexes (offline sample pretreatment with Cys for 30 min). The method was tested with the application to the natural waters and mineral well waters analysis employing CF-HG-AFS.     

Synthesis of allyl-bearing dendrimers with a resorcinarene core and their supramolecular complexes with fullerene C60

Dendritic branches of poly(arylether) with peripherial allyl chains have been attached to a resorcinarene core. Dendrimers of first, second, and third generation were synthesized. Viability to form supramolecular complexes with fullerene C60 was studied with three dendrimers of first, second, and third generation. All the compounds were characterized by 1H, 13C NMR, FTIR, UV-vis spectroscopy, MALDI-TOF, FAB+ mass spectra, and elemental analysis. Strong pi-pi, CH-pi, and n-pi interactions between the dendrimers and the fullerene C60 were detected in the supramolecular complexes by UV-vis, FTIR, and 13C CP-MAS NMR.     

Studies on the preparation and characterization of gold nanoparticles protected by dendrons

The preparation and characterization of a group of new composites, namely, gold nanoparticles-cored dendrimers were reported. These materials were obtained by the reduction of hydrogen tetrachloroaurate phase-transferred into organic phase in the presence of poly(benzyl ether) alcohol dendrons with generation 2. These materials, possessing nanometer-sized gold particles at the core and dendritic wedges radially connected to the core by Au-O bonds, were analyzed by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). A possible mechanism of the formation of Gold nanoparticles-cored dendrimers was proposed.     

Driving Catalyst Reoxidation in Wacker Cyclizations with Acetal-Based Metal-Hydride Abstractors

In traditional Wacker processes, Pd(II) becomes reduced to Pd(0) after C-O bond formation and β-H elimination and must be reoxidized to the electrophilic Pd(II) state via a stoichiometric oxidant like benzoquinone, CuCl(2), or O(2). We report herein a Pt-catalyzed Wacker-type process that regenerates the electrophilic Pt(2+) state by H(-) abstraction from a [Pt]-H using an oxocarbenium ion generated from an acetal or ketal under acidic conditions.     

Adsorption of platinum(IV) and palladium(II) from aqueous solution by thiourea-modified chitosan microspheres

The chitosan microparticles were prepared using the inverse phase emulsion dispersion method and modified with thiourea (TCS). TCS was characterized by scanning electron microscope (SEM), the Fourier transform infrared (FT-IR) spectra, sulfur elemental analysis, specific surface area and pore diameter. The effects of various parameters, such as pH, contact time, initial concentration and temperature, on the adsorption of Pt(IV) and Pd(II) by TCS were investigated. The results showed that the maximum adsorption capacity was found at pH 2.0 for both Pt(IV) and Pd(II). TCS can selectively adsorb Pt(IV) and Pd(II) from binary mixtures with Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). The adsorption reaction followed the pseudo-second-order kinetics, indicating the main adsorption mechanism of chemical adsorption. The isotherm adsorption equilibrium was well described by Langmuir isotherms with the maximum adsorption capacity of 129.9 mg/g for Pt(IV) and 112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and Pd(II) decreased with temperature increasing. The negative values of enthalpy (ΔH°) and Gibbs free energy (ΔG°) indicate that the adsorption process is exothermic and spontaneous in nature. The adsorbent was stable without loss of the adsorption capacity up to at least 5 cycles and the desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H₂SO₄ eluent was used. The results also showed that the preconcentration factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the recovery was found to be more than 97% for both precious metal ions.     

Highly enhanced electrocatalytic oxygen reduction performance observed in bimetallic palladium-based nanowires prepared under ambient, surfactantless conditions

We have employed an ambient, template-based technique that is simple, efficient, and surfactantless to generate a series of bimetallic Pd(1-x)Au(x) and Pd(1-x)Pt(x) nanowires with control over composition and size. Our as-prepared nanowires maintain significantly enhanced activity toward oxygen reduction as compared with commercial Pt nanoparticles and other 1D nanostructures, as a result of their homogeneous alloyed structure. Specifically, Pd(9)Au and Pd(4)Pt nanowires possess oxygen reduction reaction (ORR) activities of 0.49 and 0.79 mA/cm(2), respectively, which are larger than the analogous value for commercial Pt nanoparticles (0.21 mA/cm(2)). In addition, core-shell Pt~Pd(9)Au nanowires have been prepared by electrodepositing a Pt monolayer shell and the corresponding specific, platinum mass, and platinum group metal mass activities were found to be 0.95 mA/cm(2), 2.08 A/mg(Pt), and 0.16 A/mg(PGM), respectively. The increased activity and catalytic performance is accompanied by improved durability toward ORR.     

Separation and characterization of metallosupramolecular libraries by ion mobility mass spectrometry

The self-assembly of Zn(II) ions and bis(terpyridine) (tpy) ligands carrying 120° or 180° angles between their metal binding sites was utilized to prepare metallosupramolecular libraries with the connectivity. These combinatorial libraries were separated and characterized by ion mobility mass spectrometry (IM MS) and tandem mass spectrometry (MS(2)). The 180°-angle building blocks generate exclusively linear complexes, which were used as standards to determine the architectures of the assemblies resulting from the 120°-angle ligands. The latter ligand geometry promotes the formation of macrocyclic hexamers, but other n-mers with smaller (n = 5) or larger ring sizes (n = 7-9) were identified as minor products, indicating that the angles in the bis(terpyridine) ligand and within the coordinative tpy-Zn(II)-tpy bonds are not as rigid, as previously believed. Macrocyclic and linear isomers were detected in penta- and heptameric assemblies; in the larger octa- and nonameric assemblies, ring-opened conformers with compact and folded geometries were observed in addition to linear extended and cyclic architectures. IM MS(2) experiments provided strong evidence that the macrocycles present in the libraries were already formed in solution, during the self-assembly process, not by dissociation of larger complexes in the gas phase. The IM MS/MS(2) methods provide a means to analyze, based on size and shape (architecture), supramolecular libraries that are not amenable to liquid chromatography, LC-MS, NMR, and/or X-ray techniques.     

三嗪树枝状大分子的合成与表征

以二乙胺、三聚氯氰、哌嗪为单体,通过收敛法合成了两种系列的端氯基和端胺基树突,以及3代的内核为哌嗪、端基分别含8个和16个乙基的三嗪树枝状大分子,对产物进行了红外光谱（IR）、核磁共振（1H-NMR、13C-NMR）、质谱（MS）表征。该方法所需原料价廉易得,反应条件温和,无需繁杂的官能团保护与脱保护,无需色谱法分离,...     

Super‐Stable,Highly Efficient,and Recyclable Fibrous Metal–Organic Framework Membranes for Precious Metal Recovery from Strong Acidic Solutions

Precious metals such as palladium (Pd) and platinum (Pt) are marvelous materials in the fields of electronic and catalysis, but they are tapering day by day. Zr(IV)‐based metal–organic frameworks (MOFs) are competent for their recovery, notably in harsh environments, while the general powder form limits their practical application. Porous MOF‐based membranes with ultraefficient metal ion permeation, strong stability, and high selectivity are, therefore, strikingly preferred. Herein, a set of polymeric fibrous membranes incorporated with the UiO‐66 series are fabricated; their adsorption/desorption capabilities toward Pd(II) and Pt(IV) are evaluated from strongly acidic solutions; and the MOF–polymer compatibilities are investigated. Polyurethane (PU)/UiO‐66‐NH₂ showed strong acid resistance and high chemical stability, which are attributable to strong π–π interactions between PU and MOF nanoparticles with a high configuration of energy. The as‐fabricated MOF membranes show extremely good adsorption/desorption performances without ruptures/coalitions of nanofibers or leak of MOF nanoparticles, and successfully display the efficacy in a gravity‐driven or even continuous‐flow system with good recycle performance and selectivity. The as‐fabricated MOF membranes set an example of potential MOF–polymer compatibility for practical applications.     

Mass spectrometric determination of the coordination geometry of potential copper(II) surrogates for the mammalian prion protein octarepeat region

The N-terminal domain of mammalian prion proteins contains several tandem repeats of the octapeptide PHGGGWGQ, each one capable of selectively binding up to 1 equiv of Cu2+. Under saturating conditions Cu2+ is known to coordinate the HGG portion of the repeat sequence via the histidine imidazole side chain, two deprotonated amide N-atoms, and a backbone carbonyl O-atom. Using appropriate selection criteria, we have generated a short list of candidate metal ions (Co3+, Ni2+, Pd2+, Pt2+) that can serve as potential surrogates for Cu2+. The selected metal ions were screened for binding interactions with the OR-derived peptide fragment AcHGGGWNH2 (Ac = acetyl, amino acid residues in italics) using electrospray ionization mass spectrometry. The coordination geometries of these metal ions with the synthetic OR peptide were subsequently determined from fragment analysis using collision-induced dissociation tandem mass spectrometry. Our results indicate that, although Co3+, Pd2+, and Pt2+ all bind to the OR fragment via the peptide backbone to varying extents, each of these metal ions appears to associate with the peptide in a unique manner, which is distinct from the way in which Cu2+ is coordinated. This work illustrates the extremely strong selectivity for Cu2+ of this highly conserved region of the mammalian prion protein.     

HPLC separation of different generations of poly(amidoamine) dendrimers modified with various terminal groups

Polyamidoamine (PAMAM) dendrimers of different generations with various terminal groups were analyzed, for the first time, using a combination of high-performance liquid chromatography (HPLC), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) techniques. Separation of amine-terminated dendrimers from generation 1 through generation 9 (G1NH(2)-G9NH(2)) was achieved using reversed-phase HPLC with elution time increasing gradually as the density of terminal amine groups increases as a function of generation. Furthermore, separation of dendrimers with terminal amino, acetamide, hydroxyl, and carboxylate groups was obtained. It has also been shown that HPLC can be used to separate dendrimers based on some structural defects inherent during the syntheses of PAMAM dendrimers. MALDI-TOF mass spectra of G1NH(2) identify the major imperfections present during typical synthesis processes. The absolute molar masses (M(n)) and molar mass distributions of the dendrimers were measured using the SEC system equipped with multiangle laser light scattering and refractive-index detectors. Findings from this study suggest HPLC can be a vital tool for characterization and preparative separation of PAMAM dendrimers.     

Effect of Co,Pd and Pt ultra-thin films on the Ni-silicide formation: investigating the sandwich configuration

The effect of Co, Pd and Pt ultrathin films on the kinetics of the formation of Ni-silicide by reactive diffusion is investigated. 50 nm Ni/1 nm X/ 50 nm Ni (X?=?Co, Pd, Pt) deposited on Si(100) substrates are studied using in-situ and ex-situ measurements by X-ray diffraction (XRD). The presence of Co, Pd or Pt thin films in between the Ni layers delays the formation of the metal rich phase compared to the pure Ni/Si system and thus these films act as diffusion barriers. A simultaneous silicide formation (δ-Ni₂Si and NiSi phases) different from the classic sequential formation is found during the consumption of the top Ni layer for which Ni has to diffuse through the barrier. A model for the simultaneous growth in the presence of a barrier is developed, and simulation of the kinetics measured by XRD is used to determine the permeability of the different barriers. Atom probe tomography (APT) of the Ni/Pd/Ni system shows that the Pd layer is located between the Ni top layer and δ-Ni₂Si during the silicide growth, in accordance with a silicide formation controlled by Ni diffusion through the Pd layer. The effect of the barrier on the silicide formation and properties is discussed.

     

Dilute Solution Behavior of Dendrimers and Polysaccharides: SEC, ESI-MS, and Computer Modeling

Dendrimers, the most highly branched structures achievable, have found numerous uses in the chemical, biological, and pharmaceutical fields. We have employed size exclusion chromatography (SEC) with universal calibration to determine molecular weight averages, distributions, intrinsic viscosities, and structural parameters of Starburst dendrimers, dextrans, and the starch degradation polysaccharides known as maltodextrins. Comparisons have been made in the dilute solution behavior of dendrimers and polysaccharides with equivalent weight-average molecular weights. Intrinsic viscosities decreased in the order [η](dextran) > [η](dextrin) > [η](dendrimer). While the difference between dendrimer and polysaccharides may be attributed to the higher branching of the former, which leads to a higher chain density in solution, the difference between dextran and dextrin is likely a result of the variation in solution behavior of α-(1→6) vs α-(1→4) linked carbohydrates. The solution behavior of the maltodextrins studied indicates that debranching in their manufacture appears to have been more thorough than in that of β-limiting dextrins studied by other groups. Comparison of molecular radii obtained from SEC data to radii from molecular dynamics studies show Starburst dendrimers behave as θ-stars with functionality between 1 and 4. Additionally, electrospray ionization mass spectrometry was employed to determine M(w), M(n), and PD of Astramol dendrimers.