Crystal structure and charge transfer energy of the vaterite-type orthoborate YBO3:Eu

Ligand-to-metal charge transfer energies of YBO3:Eu have been investigated from the chemical bond viewpoint. The chemical bond parameters, such as the covalency, the polarizability of the chemical bond volume, and the presented charge of the ligands in the chemical bond have been quantitatively determined based on the dielectric theory of complex crystal. We calculated the environmental factor (h(e)), which is the major factor influencing the charge transfer energy in the compounds. The calculated results show that the suitable group space of YBO3 is C2/c. The method provides us with a supplementary tool to judge the proper structure when the structure of the crystal has many uncertain space groups.

Influence of gate dielectrics on charge transport in copper phthalocyanine thin-film transistors

Copper phthalocyanine organic thin-film transistors (OTFTs) were fabricated with top-gate geometry and the effects of different gate dielectrics on the transport proper-ties in OTFTs were studied. The mobility was found to be gate voltage dependent and the results showed that besides the charge density in the accumulation layer, the energetic disorder induced by gate dielectrics played an important role in determining the field-effect mobility in OTFTs.

Phosphorescence Color Tuning by Ligand, and Substituent Effects of Multifunctional Iridium(III) Cyclometalates with 9-Arylcarbazole Moieties

The synthesis, isomeric studies, and photophysical characterization of a series of multifunctional cyclometalated iridium(III) complexes containing a fluoro- or methyl-substituted 2[3-(N-plienylcarbazolyl)]pyridine molecular framework are presented. All of the complexes are thermally stable solids and highly efficient electrophosphors. The optical, electrochemical, photo-, and electrophosphorescence traits of these iridium phosphors have been studied in terms of the electronic nature and coordinating site of the aryl or pyridyl ring substituents. The correlation between the functional properties of these phosphors and the results of density functional theory calculations was made. Arising from the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such a moiety can increase the highest-occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent phosphor with 2-phenylpyridine ligands. Remarkably, the excited-state properties can be manipulated through ligand and substituent effects that allow the tuning of phosphorescence energies from bluish green to deep red.

An Extremely High Molar Extinction Coefficient Ruthenium Sensitizer in Dye-Sensitized Solar Cells: The Effects of pi-Conjugation Extension

We report a heteroleptic ruthenium complex (007) featuring the electron-rich 5-octyl-2,2'-bis(3,4-ethylenedioxythiophene) moiety conjugated with 2,2-bipyridine and exhibiting 10.7% power conversion efficiency measured at the AM1.5G conditions, thanks to the enhanced light-harvesting that is closely related to photocurrent. This C107 sensitizer has an extremely high molar extinction coefficient,of 27.4 x 10(3) M-1 cm(-1) at 559 nm in comparison to its analogue C103 (20.5 x 10(3) M-1 cm(-1) at 550 nm) or Z907 (12.2 x 10(3) M(-1)cm(-1) at 521 nm) with the corresponding 5-hexyl-3,4-ethylenedioxythiopliene- or nonyl-substituted bipyridyl unit. The augmentation of molar extinction coefficients and the bathochromic shift of low-energy absorption peaks along with the pi-conjugation extension are detailed by TD-DFT calculations. The absorptivity of mesoporous titania films grafted with Z907, C103, or C107 sublinearly increases with the molar extinction coefficient of sensitizers, which is consistent with the finding derived from the surface coverage measurements that the packing density of those sensitizers decreases with the geometric enlargement of ancillary ligands.

The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell's characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueoius DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OH-] = 0.04 M). Combining the structure changes of the porphyrin and the "four orbital" model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin Tr orbital being a different HOMO. However, its energy is close to that of the porphyrin pi orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH2 into three-banded spectra of regular metalloporphyrin.

Effect of doped dye on the charge-carrier transport and electroluminescent performance in molecularly doped polymer light-emitting diodes

The effects of the concentration of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6, 78-i,j)quinolizin-11-one (C545T) as dopant in polyfluorene (PFO) on the charge-carrier transport and electroluminescence (EL) performance were investigated by steady-state and transient EL measurements. A fully green emission from C545T was observed and the EL performance depends strongly on the C545T concentration. The mobility in the C545T-doped PFO film was determined by transient EL. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the C545T molecules. The mobility in C545T:PFO changed significantly with the C545T concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Charge carrier transporting, photoluminescent, and electroluminescent properties of zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex

Zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex is an excellent white-light-emitting material. Despite some studies devoted to this complex, no information on the real origin of the unusually broad electroluminescent (EL) emission is available. Therefore, we investigate photoluminescent and EL properties of the zinc complex. Orange phosphorescent emission at 580 nm was observed for the complex in thin film at 77 K, whereas only fluorescent emission was obtained at room temperature. Molecular orbitals, excitation energy, and emission energy of the complex were investigated using quantum chemical calculations. We fabricated the device with a structure of ITO/F16CuPc(5.5 nm)/Zn-complex/Al, where F16CuPc is hexadecafluoro copper phthalocyanine. The EL spectra varied strongly with the thickness of the emissive layer. We observed a significant change in the emission spectra with the viewing angles. Optical interference effects and light emission originating both from fluorescence and from phosphorescence can explain all of the observed phenomena, resulting in the broad light emission for the devices based on the Zn complex. We calculated the charge transfer integral and the reorganization energy to explain why the Zn complex is a better electron transporter than a hole transporter.

Effect of DNA flanking sequence on charge transport in short DNA duplexes

Several factors can influence charge transport (CT)-mediated DNA, such as sequence, distance, base stacking, base pair mismatch, conformation, tether length, etc. However, the DNA context effect or how flanking sequences influence redox active drugs in the DNA CT reaction and later in DNA enzymatic repair and synthesis is still not well understood. The set of seven DNA molecules in this study have been characterized well for the study of flanking sequence effects. These DNA duplexes are formed from self-complementary strands and contain the common central four-base sequence 5'-A-G-C-T-3', flanked on both sides by either (AT)(n) or (AA)(n) (n = 2, 3, or 4) or AA(AT)(2). UV-vis, fluorescence, UV melting, circular dichroism, and cyclic voltammetry experiments were used to study the flanking sequence effect on CT-mediated DNA by using daunomycin or adriamycin cross-linked with these seven DNA molecules. Our results showed that charge transport was related to the flanking sequence, DNA melting free energy, and ionic strength. For (AA)(n) or (AT)(n) species of the same length, (AA)(n) series were more stable and more efficient CT was observed through the (AA)(n) series. The same trend was observed for (AA)(n) and (AT)(n) series at different ionic strengths, further supporting the idea that flanking sequence can result in different base stacking and modulate charge transport through these seven DNA molecules.

Negative differential resistance and multilevel memory effects in organic devices

Negative differential resistance ( NDR) and multilevel memory effects were obtained in organic devices consisting of an anthracene derivative, 9,10-bis-{ 9,9-di-[ 4-(phenyl-p-tolyl-amino)-phenyl]-9H-fluoren-2-yl}-anthracene ( DAFA), sandwiched between Ag and ITO electrodes. The application of a negative bias voltage leads to negative differential resistance in current-voltage characteristics and different negative voltages produce different conductance currents, resulting in the multilevel memory capability of the devices. The NDR property has been attributed to charge trapping at the DAFA/Ag interface. This opens up a wide range of application possibilities of such organic-based NDR devices in memory and logic circuits.

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA(+)) or ClO4- is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k(12), is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K4Fe(CN)(6) in water when the concentration of TCNQ in the DCE phase is in excess. The k(12) dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ and ferricyanide, k(21), is also obtained by SECM and these results cannot be explained by the same manner.

Synthesis, characterization and crystal structure of a charge transfer salt based on 1.3-cyclopentadiene tetrabutylammoniumdodecamolybdosilicoate

A charge transfer salt, (Bu4N)(4) (C5H6)[(HSiMo11MoO40)-Mo-VI-O-V] has been photochemically synthesized from (Bu4N)(4)SiMo12O40 and 1.3-cyclopentadiene and Characterized, by elemental analysis, IR spectra, solid diffusion reflectance electronic spectra, CV and ESR. The X-ray crystal structure revealed that the title complex crystal data are as follows: triclinic, space group P (1) over bar, a = 14.347(3), b = 14.423(3), c = 27.158(5) Angstrom, alpha = 96.90(3), beta = 104.18(3), gamma = 98.20(3)degrees, V = 5322(2) Angstrom (3), Z = 2, M-r = 2855. 30, D-c = 1.782g.cm(-3), F(000) = 2860, R = 0.0719, wR = 0.198. The title compound is composed of 1.3-cyclopentadiene, four tetrabutylammonium and [(SiMo11MoO40)-Mo-VI-O-V](4-) anion.

Effects of pressure and molecular weight on the miscibility of polystyrene and cyclohexane

With the aid of Sanchez-Lacombe lattice fluid theory (SLLFT), the phase diagrams were calculated for the system cyclohexane (CH)/polystyrene (PS) with different molecular weights at different pressures. The experimental data is in reasonable agreement with SLLFT calculations. The total Gibbs interaction energy, g*(12) for different molecular weights PS at different pressures was expressed, by means of a universal relationship, as g(12)* =f(12)* + (P - P-0) nu*(12) demixing curves were then calculated at fixed (near critical) compositions of CH and PS systems for different molecular weights. The pressures of optimum miscibility obtained from the Gibbs interaction energy are close to those measured by Wolf and coworkers. Furthermore, a reasonable explanation was given for the earlier observation of Saeki et al., i.e., the phase separation temperatures of the present system increase with the increase of pressure for the low molecular weight of the polymer whereas they decrease for the higher molecular weight polymers. The effects of molecular weight, pressure, temperature and composition on the Flory Huggins interaction parameter can be described by a general equation resulting from fitting the interaction parameters by means of Sanchez-Lacombe lattice fluid theory.

Preliminary study on the charge transfer and bond ionicity of binary crystals

Charge transfer and bond ionicity of some monovalent, divalent, and trivalent binary crystals of A(N)B(8-N) type have been investigated using the self-consistent method. The method divides the binary crystal systems into two subsystems which contain only one kind of element each in physical space. The charge transfer values are obtained by adjusting the charge in a self-consistent way. Based on the obtained charge transfer values, an empirical formula for bond ionicity has been proposed. It has been shown that the present results for bond ionicity are in good agreement with the previous theoretical study delivered by Levine and Pauling. The results also indicate that a large magnitude of charge transfer (or less excess charge in the bonding region) gives rise to high bond ionicity (or low bond covalency); this agrees well with the viewpoint that the excess charge in the bonding region is the origin of the formation of bond covalency. (C) 1998 American Institute of Physics. [S0021-9606(98)00837-X].

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.