An Efficient Electrochemical Sensor Driven by Hierarchical Hetero-Nanostructures Consisting of RuO2 Nanorods on WO3 Nanofibers for Detecting Biologically Relevant Molecules.

By means of electrospinning with the thermal annealing process, we investigate a highly efficient sensing platform driven by a hierarchical hetero-nanostructure for the sensitive detection of biologically relevant molecules, consisting of single crystalline ruthenium dioxide nanorods (RuO2 NRs) directly grown on the surface of electrospun tungsten trioxide nanofibers (WO3 NFs). Electrochemical measurements reveal the enhanced electron transfer kinetics at the prepared RuO2 NRs-WO3 NFs hetero-nanostructures due to the incorporation of conductive RuO2 NRs nanostructures with a high surface area, resulting in improved relevant electrochemical sensing performances for detecting H2O2 and L-ascorbic acid with high sensitivity.

Selectivity enhancement of amperometric nitric oxide detection via shape-controlled electrodeposition of platinum nanostructures.

Nitric oxide (NO) is a biologically multifunctional gaseous signaling molecule. For electrochemical NO detections, complex membranes are commonly adopted to acquire the selectivity for NO over other oxidizable biological species. In this study, we demonstrate the improved selectivity in amperometric NO measurements at nanostructured Pt. The Pt layers were electrodeposited on Au substrate electrodes at a constant potential (-0.2 V vs. Ag/AgCl) with a constant deposition charge (0.08 C). The various distinctive nanostructures of Pt deposits were obtained via either changing the precursor concentrations (from 5 to 75 mM K2PtCl4) or using a different precursor (75 mM H2PtCl6). With a higher K2PtCl4 concentration, the Pt deposition became less sharp and the smoothest Pt was deposited with 75 mM H2PtCl6. The most greatly sharp-pointed nanostructures were generated with the lowest precursor concentration (5 mM K2PtCl4) and exhibited the highest sensitivity, which was attributed to the hydrophobic property of sharply nanostructured Pt. A hydrophobic neutral gas molecule, NO, possibly has a more favorable access to the inner surface of more hydrophobic Pt deposition and eventually increases the oxidation current. NO current sensitivity was enhanced at the more hydrophobic Pt surface, whereas the oxidation currents of acetaminophen, l-ascorbic acid, nitrite and hydrogen peroxide, four oxidizable biological interfering species, were independent of the Pt nanostructure. Conclusively, the enhanced amperometric selectivity to NO was achieved by the simple electrodeposition method without any additional membranes.

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation.

NiO/NiCo2O4 nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N2 adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (∼20 m2 g-1) than expected for a flat-surface structure (<15 m2 g-1). Herein, we present a study of the catalytic activity of our novel NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo2O4 is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo2O4 for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo2O4 tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

Enhanced electrochemical performance of a ZnO-MnO composite as an anode material for lithium ion batteries.

A ZnO-MnO composite was synthesized using a simple solvothermal method combined with a high-temperature treatment. To observe the phase change during the heating process, in situ high-temperature XRD analysis was performed under vacuum conditions. The results indicated that ZnMn2O4 transformed into the ZnO-MnO composite phase starting from 500 °C and that this composite structure was retained until 700 °C. The electrochemical performances of the ZnO-MnO composite electrode were evaluated through galvanostatic discharge-charge tests and cyclic voltammetry analysis. Its initial coulombic efficiency was significantly improved to 68.3% compared to that of ZnMn2O4 at 54.7%. Furthermore, the ZnO-MnO composite exhibited improved cycling performance and enhanced rate capability compared with untreated ZnMn2O4. To clarify the discharge-charge mechanism of the ZnO-MnO composite electrode, the structural changes during the charge and discharge processes were also investigated using ex situ XRD and TEM.

RuO2-ReO3 composite nanofibers for efficient electrocatalytic responses.

We present a facile synthetic route to ruthenium dioxide (RuO2)-rhenium oxide (ReO3) electrospun composite nanofibers and their electrocatalytic responses for capacitance and H2O2 sensing. The contents of rhenium oxide of electrospun ruthenium dioxide (RuO2) were carefully controlled by an electrospinning process with the preparation of the precursor solutions followed by the thermal annealing process in air. The electrochemical applications of RuO2-ReO3 electrospun composite nanofibers were then investigated by modifying these materials on the surface of glassy carbon (GC) electrodes, RuO2-ReO3(n)/GC (n = 0.0, 0.07, 0.11, and 0.13), where n denotes the relative atomic ratio of Re to the sum of Ru and Re. Specific capacitance and H2O2 reduction sensitivity were remarkably enhanced depending on the amount of ReO3 increased. Among the four compositions of RuO2-ReO3(n), RuO2-ReO3(0.11)/GC showed the highest performances, i.e., a 20.9-fold higher specific capacitance (205 F g(-1) at a potential scan rate (v) of 10 mV s(-1); a capacity loss of 19% from v = 10 to 2000 mV s(-1)) and a 7.6-fold higher H2O2 reduction sensitivity (668 µA mM(-1) cm(-2), normalized by GC disk area), respectively, compared to only RuO2/GC.

Spongelike nanoporous Pd and Pd/Au structures: facile synthesis and enhanced electrocatalytic activity.

This paper reports the facile synthesis and characterization of spongelike nanoporous Pd (snPd) and Pd/Au (snPd/Au) prepared by a tailored galvanic replacement reaction (GRR). Initially, a large amount of Co particles as sacrificial templates was electrodeposited onto the glassy carbon surface using a cyclic voltammetric method. This is the key step to the subsequent fabrication of the snPd/Au (or snPd) architectures by a surface replacement reaction. Using Co films as sacrificial templates, snPd/Au catalysts were prepared through a two-step GRR technique. In the first step, the Pd metal precursor (at different concentrations), K2PdCl4, reacted spontaneously to the formed Co frames through the GRR, resulting in a snPd series. snPd/Au was then prepared via the second GRR between snPd (prepared with 27.5 mM Pd precursor) and Au precursor (10 mM HAuCl4). The morphology and surface area of the prepared snPd series and snPd/Au were characterized using spectroscopic and electrochemical methods. Rotating disk electrode (RDE) experiments for oxygen reduction in 0.1 M NaOH showed that the snPd/Au has higher catalytic activity than snPd and the commercial Pd-20/C and Pt-20/C catalysts. Rotating ring-disk electrode (RRDE) experiments reconfirmed that four electrons were involved in the electrocatalytic reduction of oxygen at the snPd/Au. Furthermore, RDE voltammetry for the H2O2 oxidation/reduction was used to monitor the catalytic activity of snPd/Au. The amperometric i-t curves of the snPd/Au catalyst for a H2O2 electrochemical reaction revealed the possibility of applications as a H2O2 oxidation/reduction sensor with high sensitivity (0.98 mA mM(-1) cm(-2) (r = 0.9997) for H2O2 oxidation and -0.95 mA mM(-1) cm(-2) (r = 0.9997) for H2O2 reduction), low detection limit (1.0 µM), and a rapid response (<∼1.5 s).

Oxidation-state dependent electrocatalytic activity of iridium nanoparticles supported on graphene nanosheets.

Nanocomposites of iridium nanoparticles (Ir NPs), supported on graphene nanosheets, are synthesized and their electrocatalytic acitivities in the oxygen reduction reaction (ORR) are studied depending on their Ir oxidation state. Graphene functionalized with poly(vinyl pyrrolidone) (pRGO) is a suitable support for Ir NPs, producing well-monodispersed Ir NPs anchored strongly on the pRGO surface (Ir NP/pRGO) with a very high density. This was confirmed by scanning electron microscopy and transmission electron microscopy. The ORR activity of the Ir NP/pRGO nanocomposites in 0.5 M H2SO4 solution was observed to be dependent on the oxidation state of the immobilized Ir NPs. In fact, the nanocomposite composed of Ir(0) metal NPs, rather than Ir oxide (IrOx) NPs, exhibits higher ORR activity, such as more positive onset potential, higher and flatter limiting current density, a greater n value, and a sharper curve shape in the rotating disk electrode voltammetry experiments. Higher ORR activity of Ir is ascribed to the stronger adsorption of oxygen on the surface of Ir compared to IrOx. The practical stability of the Ir NP/pRGO composite was also confirmed under O2 saturated/acidic conditions.

Synthesis and electrocatalytic activity of highly porous hollow palladium nanoshells for oxygen reduction in alkaline solution.

A series of hollow Pd nanoshells are prepared by employing Co nanoparticles as sacrificial templates with different concentrations of a Pd precursor (1, 6, 12, 20, and 40 mM K2PdCl4), denoted hPd-X (X: concentration of K2PdCl4 in mM unit). The synthesized hPd series are tested as a cathodic electrocatalyst for oxygen reduction reaction (ORR) in alkaline solution. The morphology and surface area of the hPd catalysts are characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and cyclic voltammetry (CV). Rotating disk electrode (RDE) voltammetric studies show that the hPd-20 (prepared using 20 mM K2PdCl4) has the highest ORR activity among all the hPd series, while being comparable to commercial Pd and Pt catalysts (E-TEK). The more facilitated ORR at hPd-20 is presumably induced by the enhanced Pd surface area and efficiently high porosity of Pd nanoshells.

Hierarchically driven IrO2 nanowire electrocatalysts for direct sensing of biomolecules.

Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO(2)) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H(2)O(2)) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules.

Single carbon fiber decorated with RuO2 nanorods as a highly electrocatalytic sensing element.

We demonstrate highly efficient electocatalytic activities of single crystalline RuO(2) nanorods grown on carbon fiber (CF), i.e., RuO(2) nanorod-CF hybrid microelectrode, prepared by a simple thermal annealing process from the Ru(OH)(3) precursor at 300 °C. The general electrochemical activity of a RuO(2) nanorod-CF microelectrode represents faster electron transfer for the [Fe(CN)(6)](3-/4-) couple than that of the bare CF microelectrode which are confirmed from the cyclic voltammetry (CV) measurement. Also, the amperometric response for the H(2)O(2) oxidation is remarkably facilitated at the RuO(2) nanorod-CF microelectrode by not only the enlarged surface area but the high electrocatalytic activity of the RuO(2) nanorod material itself. Furthermore, a single microelectrode of RuO(2) nanorod-CF exhibits the superior tolerance to Cl(-) ion poisoning unlike Pt-based electrocatalysts, indicating the promising sensor candidate in physiological conditions.

Electrocatalytic activity of nanoporous Pd and Pt: effect of structural features.

The electrocatalytic activities of nanoporous palladium (npPd) and platinum (npPt) for oxygen reduction reaction (ORR) under alkaline conditions and hydrogen peroxide electrochemical reactions under neutral conditions were examined. npPd and npPt were prepared by the electrochemical deposition of each metal from the corresponding metal precursor in the presence of reverse micelles of Triton X-100, directing highly porous microstructures. The nanoporous catalysts showed excellent electrocatalytic activity for both the ORR and hydrogen peroxide electrochemical oxidation/reduction due to the increased active surface area. In particular, the npPd exhibited superior ORR activity (i.e., more positive onset and half-wave potentials, higher current density and greater number of electrons transferred) despite the smaller roughness factor than the npPt and commercial Pt. The catalytic activity for the hydrogen peroxide electrochemical reactions was also higher while using npPd (i.e., faster electrode reaction kinetics, increased current densities, etc.) compared to npPt. The higher catalytic activity of npPd than that of npPt suggests an advantage of the unique npPd structure, composed of nano- as well as micro-porosity, in facilitating mass transport through the porous metal layer. The npPd exhibited amperometric current responses, induced by the oxidation as well as reduction of hydrogen peroxide, linearly proportional to the hydrogen peroxide concentration with a rapid response time (<~2 s), high sensitivity, and low detection limit (<1.8 µM).

Structural transformation between rutile and spinel crystal lattices in Ru-Co binary oxide nanotubes: enhanced electron transfer kinetics for the oxygen evolution reaction.

A variety of binary Ru-Co mixed oxide nanotubes (RuxCo1-xOy with x = 0.19, 0.33, 0.47, 0.64 and 0.77) were readily synthesized via electrospinning and subsequent calcination. RuxCo1-xOy nanotubes (0 < x < 0.77) were composed of both rutile (Ru in RuO2 is replaced with Co) and spinel (Co in Co3O4 is replaced with Ru) structures. This elemental substitution created oxygen vacancies in the rutile structure and also resulted in the incorporation of Ru3+ in the octahedral sites of the spinel structure. The as-prepared RuxCo1-xOy nanotubes were investigated for oxygen evolution reaction (OER) electrocatalytic activity in 1.0 M HClO4 aqueous solution. RuxCo1-xOy nanotubes with x≥ 0.47 presented an excellent OER activity comparable to pure RuO2, known to be the best OER catalyst. Even after more than half of the noble/active Ru content was replaced with cheap/less-active Co, Ru0.47Co0.53Oy showed a good OER activity and a greatly improved stability compared to RuO2 under the continuous OER. These attractive catalytic properties of RuxCo1-xOy can be attributed to the relatively large surface area of the tubular morphology and the substituted structures, presenting feasibility as a practical and economical OER catalyst.

Amperometric Sensing of Carbon Monoxide: Improved Sensitivity and Selectivity via Nanostructure-Controlled Electrodeposition of Gold.

A series of gold (Au) nanostructures, having different morphologies, were fabricated for amperometric selective detection of carbon monoxide (CO), a biologically important signaling molecule. Au layers were electrodeposited from a precursor solution of 7 mM HAuCl4 with a constant deposition charge (0.04 C) at various deposition potentials. The obtained Au nanostructures became rougher and spikier as the deposition potential lowered from 0.45 V to 0.05 V (vs. Ag/AgCl). As prepared Au layers showed different hydrophobicity: The sharper morphology, the greater hydrophobicity. The Au deposit formed at 0.05 V had the sharpest shape and the greatest surface hydrophobicity. The sensitivity of an Au deposit for amperometric CO sensing was enhanced as the Au surface exhibits higher hydrophobicity. In fact, CO selectivity over common electroactive biological interferents (L-ascorbic acid, 4-acetamidophenol, 4-aminobutyric acid and nitrite) was improved eminently once the Au deposit became more hydrophobic. The most hydrophobic Au was also confirmed to sense CO exclusively without responding to nitric oxide, another similar gas signaling molecule, in contrast to a hydrophobic platinum (Pt) counterpart. This study presents a feasible strategy to enhance the sensitivity and selectivity for amperometric CO sensing via the fine control of Au electrode nanostructures.

Highly Catalytic Electrochemical Oxidation of Carbon Monoxide on Iridium Nanotubes: Amperometric Sensing of Carbon Monoxide.

The nanotubular structures of IrO2 and Ir metal were successfully synthesized without any template. First, IrO2 nanotubes were prepared by electrospinning and post-calcination, where a fine control of synthetic conditions (e.g., precursor concentration and solvent composition in electrospinning solution, temperature increasing rate for calcination) was required. Then, a further thermal treatment of IrO2 nanotubes under hydrogen gas atmosphere produced Ir metal nanotubes. The electroactivity of the resultant Ir metal nanotubes was investigated toward carbon monoxide (CO) oxidation using linear sweep voltammetry (LSV) and amperometry. The anodic current response of Ir metal nanotubes was linearly proportional to CO concentration change, with a high sensitivity and a short response time. The amperometric sensitivity of Ir metal nanotubes for CO sensing was greater than a nanofibrous counterpart (i.e., Ir metal nanofibers) and commercial Pt (20 wt% Pt loading on carbon). Density functional theory calculations support stronger CO adsorption on Ir(111) than Pt(111). This study demonstrates that metallic Ir in a nanotubular structure is a good electrode material for the amperometric sensing of CO.

Elucidation of the structure of a highly active catalytic system for CO2/epoxide copolymerization: a salen-cobaltate complex of an unusual binding mode.

Salen-type ligands comprised of ethylenediamine or 1,2-cyclohexenediamine, along with an salicylaldehyde bearing a methyl substituent on its 3-position and a -[CR(CH(2)CH(2)CH(2)N(+)Bu(3))(2)] (R = H or Me) on its 5-position, unexpectedly afford cobalt(III) complexes with uncoordinated imines. In these complexes, two salen-phenoxys and two 2,4-dinitrophenolates (DNPs), which counter the quaternary ammonium cations, coordinate persistently with cobalt, while two other DNPs are fluxional between a coordinated and an uncoordinated state in THF at room temperature. The complexes of this binding mode show excellent activities in carbon dioxide/propylene oxide copolymerization (TOF, 8300-13,000 h(-1)) but with some fluctuation in induction times (1-10 h), depending on how dry the system is. The induction time is shortened (<1.0 h) and activity is increased approximately 1.5 times upon the replacement of the two fluxional DNPs with 2,4-dinitrophenol-2,4-dinitrophenolate homoconjugation ([DNP...H...DNP](-)). Imposing steric congestion either by replacing the methyl substituent on the salicylaldehyde with tert-butyl or by employing H(2)NCMe(2)CMe(2)NH(2) instead of ethylenediamine or 1,2-cyclohexenediamine results in conventional imine-coordinating complexes, which show lower activities than uncoordinated imine complexes.

Boosted Electron-Transfer Kinetics of Hydrogen Evolution Reaction at Bimetallic RhCo Alloy Nanotubes in Acidic Solution.

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co2RhO4 nanotubes. The reduction was conducted by thermal annealing of the Co2RhO4 nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO4 solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm-2 (-22 mV) and a small Tafel slope (-24.1 mV dec-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.

Single-Step Electrospun Ir/IrO2 Nanofibrous Structures Decorated with Au Nanoparticles for Highly Catalytic Oxygen Evolution Reaction.

Nanocomposites of gold (Au) and iridium (Ir) oxide with various compositions (denoted as Au xIr1- xO y, x = 0.05, 0.10, or 0.33, Au precursor molar ratio to Ir precursor) were synthesized via electrospinning and subsequent calcination method with two different solvent composition ratios of ethanol to N, N-dimethylformamide (DMF) in the electrospinning solution (ethanol/DMF = 70:30 or 50:50% v/v). Simple single-step electrospinning successfully fabricated a hierarchical nanostructure having Au nanoparticles formed on fibrous main frames of Ir/IrO2. Different solvent composition in the electrospinning solution induced the formation of main frames with distinct nanostructures; nanoribbons (Au xIr1- xO y-70) with ethanol/DMF = 70:30; and nanofibers (Au xIr1- xO y-50) with ethanol/DMF = 50:50. The pure Ir or Au counterparts (IrO y and Au) were also prepared by the same synthetic procedure as Au xIr1- xO y. Oxygen evolution reaction (OER) activities of as-synthesized Au xIr1- xO y were investigated in 0.5 M H2SO4 and compared to those of IrO y, Au, and commercial iridium (Ir/C, 20% Ir loading on Vulcan carbon). Among them, Au0.10Ir0.90O y-50 exhibited the best OER activity, even better than previously reported catalysts containing both Ir and Au. The high OER activity of Au0.10Ir0.90O y-50 was mainly attributed to the fiber frame structure and the optimal interfacial areas between Au and Ir/IrO2, which are electrophilic OER active sites. The stability of Au0.10Ir0.90O y-50 was also evaluated to be much higher than that of Ir/C during OER. The current study suggests that the presence of Au on the Ir/IrO2 surface improves the OER activity of Ir/IrO2.

Correction: Single phase of spinel Co2RhO4 nanotubes with remarkably enhanced catalytic performance for the oxygen evolution reaction.

Correction for 'Single phase of spinel Co2RhO4 nanotubes with remarkably enhanced catalytic performance for the oxygen evolution reaction' by So Yeon Kim et al., Nanoscale, 2019, 11, 9287-9295.

Single phase of spinel Co2RhO4 nanotubes with remarkably enhanced catalytic performance for the oxygen evolution reaction.

We report the effective crystal growth for a unique single phase of spinel cobalt rhodium oxide (Co2RhO4) nanotubes via the electrospinning process combined with the thermal annealing process. In the spinel structure of the electrospun Co2RhO4 nanotubes, Co3+ cations and Rh3+ cations randomly occupy the octahedral sites, while the remaining half of the Co2+ cations occupy the centres of the tetrahedral sites as proved by microscopic and spectroscopic observations. Furthermore, electrospun spinel Co2RhO4 nanotubes exhibit excellent catalytic performances with the least positive onset potential, greatest current density, and low Tafel slope which are even better than those of the commercial Ir/C electrocatalyst for the oxygen evolution reaction (OER) in alkaline solution. Our demonstration of significantly enhanced OER activity with a single phase of electrospun spinel Co2RhO4 nanotubes thus opens up the broad applicability of our synthetic methodology for accessing new OER catalysis.

Generation of blue light-emitting zinc complexes by band-gap control of the oxazolylphenolate ligand system: syntheses, characterizations, and organic light emitting device applications of 4-coordinated bis(2-oxazolylphenolate) zinc(II) complexes.

Color-tunable Zn(II) complexes of the type Zn( N,O-OPh (OxZ)ArX) 2 ( 5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe 2 a, OMe b, Ph c, Cl d, F 2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation. Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) band gaps and electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO-LUMO band gap is seen from electron-donating to electron-withdrawing functional groups, NMe 2 < OMe < Ph < Cl < F 2 < CN. An emission peak with a maximum at 455 nm was achieved when the most electron-withdrawing group (cyano) was applied to the oxazolylphenolate ligand system. Density-functional theory (DFT) calculations on the HOMOs and LUMOs for this series lead to a conclusion similar to that arrived at from a blue-shift trend observed in UV data and trends in the CVs. The 4-coordinated zinc complex ( 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m (2) at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/ 5c/BCP/Alq 3/LiF/Al. On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in the successful fabrication of a multilayered device of ITO/ 5a/DPVBI/Alq 3/LiF/Al with an efficiency of 7000 cd/m (2) at 13 V with 2.0 cd/A.