Theoretical characterization of a typical hole/exciton-blocking material bathocuproine and its analogues

The structural, electronic, and carrier transport properties of bathocuproine (BCP), which is a typical hole/exciton-blocking material applied in organic light-emitting diodes (OLEDs), have been investigated based on density functional theory (DFT) and ab initio HF method. The detail characterizations of frontier electronic structure and lowest-energy optical transitions have been studied by means of time-dependent density functional theory (TD-DFT). Five BCP analogues, o-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-diphenyl-1,10-phenanthroline (3), 4,7-diphenyl-1,10-phenanthroline (4), and 2,9-bis(trifluoromethyl)-1,10-phenanthroline (5) have also been studied in order to select more suitable candidates of efficient hole-blocking materials. The calculated results showed that rigid planar structures, conjugate degrees, and substitute groups play crucial roles in the hole/exciton-blocking and electron-transport properties of these materials. The calculated geometries, ionization energies (IP), and energy gap between the singlet ground state and triplet excited state (E(T1)) were well in agreement with the experimental results. On the basis of the incoherent transport model, the calculated electron mobility of BCP is 1.79 x 10(-2) cm(2)/(V s), which is comparable to experimental results of 1.1 x 10(-3) cm(2)/(V s). The electron mobilities for compounds 1, 4, and 5 are 3.45 x 10(-2), 2.90 x 10(-2), and 1.40 x 10(-2) cm(2)/(V s), respectively. The calculated results indicated that compounds 1, 4, and 5 may be more effective hole/exciton-blocking materials than BCP.     

High-mobility field-effect transistors from large-area solution-grown aligned C60 single crystals

Field-effect transistors based on single crystals of organic semiconductors have the highest reported charge carrier mobility among organic materials, demonstrating great potential of organic semiconductors for electronic applications. However, single-crystal devices are difficult to fabricate. One of the biggest challenges is to prepare dense arrays of single crystals over large-area substrates with controlled alignment. Here, we describe a solution processing method to grow large arrays of aligned C(60) single crystals. Our well-aligned C(60) single-crystal needles and ribbons show electron mobility as high as 11 cm(2)V(-1)s(-1) (average mobility: 5.2 ± 2.1 cm(2)V(-1)s(-1) from needles; 3.0 ± 0.87 cm(2)V(-1)s(-1) from ribbons). This observed mobility is ~8-fold higher than the maximum reported mobility for solution-grown n-channel organic materials (1.5 cm(2)V(-1)s(-1)) and is ~2-fold higher than the highest mobility of any n-channel organic material (~6 cm(2)V(-1)s(-1)). Furthermore, our deposition method is scalable to a 100 mm wafer substrate, with around 50% of the wafer surface covered by aligned crystals. Hence, our method facilitates the fabrication of large amounts of high-quality semiconductor crystals for fundamental studies, and with substantial improvement on the surface coverage of crystals, this method might be suitable for large-area applications based on single crystals of organic semiconductors.     

Tuning orbital energetics in arylene diimide semiconductors. materials design for ambient stability of n-type charge transport

Structural and electronic criteria for ambient stability in n-type organic materials for organic field-effect transistors (OFETs) are investigated by systematically varying LUMO energetics and molecular substituents of arylene diimide-based materials. Six OFETs on n+-Si/SiO2 substrates exhibit OFET response parameters as follows: N,N'-bis(n-octyl)perylene-3,4:9,10-bis(dicarboximide) (PDI-8): mu = 0.32 cm2 V(-1) s(-1), Vth = 55 V, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dibromoperylene-3,4:9,10-bis(dicarboximide) (PDI-8Br2): mu = 3 x 10(-5) cm2 V(-1) s(-1), Vth = 62 V, I(on)/I(off) = 10(3); N,N'-bis(n-octyl)-1,6,7,12-tetrachloroperylene-3,4:9,10-bis(dicarboximide) (PDI-8Cl4): mu = 4 x 10(-3) cm2 V(-1) (s-1), Vth = 37 V, I(on)/I(off) = 10(4); N,N'-bis(n-octyl)-2-cyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN): mu = 4.7 x 10(-3) cm2 V(-1) s(-1), Vth = 28, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2): mu = 0.13 cm2 V(-1) s(-1), Vth = -14 V, I(on)/I(off) = 10(3); and N,N'-bis(n-octyl)-2,6-dicyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN2): mu = 0.15 cm2 V(-1) s(-1), Vth = -37 V, I(on)/I(off) = 10(2). Analysis of the molecular geometries and energetics in these materials reveals a correlation between electron mobility and substituent-induced arylene core distortion, while Vth and I(off) are generally affected by LUMO energetics. Our findings also indicate that resistance to ambient charge carrier trapping observed in films of N-(n-octyl)arylene diimides occurs at a molecular reduction potential more positive than approximately -0.1 V (vs SCE). OFET threshold voltage shifts between vacuum and ambient atmosphere operation suggest that, at E(red1) < -0.1 V, the interfacial trap density increases by greater than approximately 1 x 10(13) cm(-2), while, for semiconductors with E(red1) > -0.1 V, the trap density increase is negligible. OFETs fabricated with the present n-type materials having E(red1) > -0.1 V operate at conventional gate biases with minimal hysteresis in air. This reduction potential corresponds to an overpotential for the reaction of the charge carriers with O2 of approximately 0.6 V. N,N'-1H,1H-Perfluorobutyl derivatives of the perylene-based semiconductors were also synthesized and used to fabricate OFETs, resulting in air-stable devices for all fluorocarbon-substituted materials, despite generally having E(red1) < -0.1 V. This behavior is consistent with a fluorocarbon-based O2 barrier mechanism. OFET cycling measurements in air for dicyanated vs fluorinated materials demonstrate that energetic stabilization of the charge carriers results in greater device longevity in comparison to the OFET degradation observed in air-stable semiconductors with fluorocarbon barriers.     

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.     

Dye-sensitized photocathodes: efficient light-stimulated hole injection into p-GaP under depletion conditions

The steady-state photoelectrochemical responses of p-GaP photoelectrodes immersed in aqueous electrolytes and sensitized separately by six triphenylmethane dyes (rose bengal, rhodamine B, crystal violet, ethyl violet, fast green fcf, and brilliant green) have been analyzed. Impedance measurements indicated that these p-GaP(100) photoelectrodes operated under depletion conditions with an electric field of ～8.5 × 10(5) V cm(-1) at the p-GaP/solution interface. The set of collected wavelength-dependent quantum yield responses were consistent with sensitization occurring specifically from adsorbed triphenylmethane dyes. At high concentrations of dissolved dye, the measured steady-state photocurrent-potential responses collected at sub-bandgap wavelengths suggested unexpectedly high (>0.1) net internal quantum yields for sensitized hole injection. Separate measurements performed with rose bengal adsorbed on p-GaP surfaces pretreated with (NH(4))(2)S verified efficient sensitized hole injection. A modified version of wxAMPS, a finite-difference software package, was utilized to assess key operational features of the sensitized p-GaP photocathodes. The net analysis showed that the high internal quantum yield values inferred from the experimental data were most likely afforded by the internal electric field present within p-GaP, effectively sweeping injected holes away from the interface and minimizing their participation in deleterious pathways that could limit the net collection yield. These simulations defined effective threshold values for the charge carrier mobilities (≥10(-6) cm(2) V(-1) s(-1) and ≥10(-1) cm(2) V(-1) s(-1) at dopant densities of 10(18) and 10(13) cm(-3), respectively), hole injection rate constants (≥10(12) s(-1)), and surface trap densities (10(12) cm(-2)) needed to attain efficient hole collection with the quality of p-GaP materials used here. The cumulative experimental and modeling data thus provide insight on design strategies for assembling new types of dye-sensitized photocathodes that operate under depletion conditions.     

Measurement of electroosmotic flow in plastic imprinted microfluid devices and the effect of protein adsorption on flow rate.

Several commercially available plastic materials were used as substrates in the fabrication of microfluid channels for biochemical analysis. Protocols for fabrication using the wire-imprinting method are reported for polystyrene, polymethylmethacrylate and a copolyester material. Channel sealing was accomplished by low-temperature bonding of a substrate of similar material; therefore, each channel was composed of a single material on all sides. The electroosmotic flow in 25-microm imprinted channels was evaluated for each substrate material. The copolyester material exhibited the highest electroosmotic flow mobility of 4.3 x 10(-4) cm2 V(-1) s(-1) which is similar to that previously reported for fused-silica capillaries. Polystyrene exhibited the lowest electroosmotic flow mobility of 1.8 x 10(-4) cm2 V(-1) s(-1). Plots of linear velocity versus applied electric field strength were linear from 100 V cm(-1) to 500 V cm(-1) indicating that heat dissipation is effective for all substrates in this range. Electroosmotic flow was reevaluated in the plastic channels following incubation in antibody solution to access the non-specific binding characteristics of a common biochemical reagent onto the substrate materials. All materials tested showed a high degree of non-specific adsorption of IgG as indicated by a decrease in the electroosmotic flow mobility in post-incubation testing.     

Synthesis and characterization of a thiazolo[5,4-d]thiazole-based copolymer for high performance polymer solar cells

A highly processable, new semiconducting polymer, PCDTTz, based on alternating thiazolothiazole and carbazole units was synthesized. The new polymer exhibited a field-effect carrier mobility of up to 3.8 × 10(-3) cm(2) V(-1) s(-1) and bulk heterojunction solar cells made from PCDTTz produced a power conversion efficiency of 4.88% under AM 1.5 G (100 mW cm(-2)) conditions.     

Bithiophene-imide-based polymeric semiconductors for field-effect transistors: synthesis, structure-property correlations, charge carrier polarity, and device stability

Developing new high-mobility polymeric semiconductors with good processability and excellent device environmental stability is essential for organic electronics. We report the synthesis, characterization, manipulation of charge carrier polarity, and device air stability of a new series of bithiophene-imide (BTI)-based polymers for organic field-effect transistors (OFETs). By increasing the conjugation length of the donor comonomer unit from monothiophene (P1) to bithiophene (P2) to tetrathiophene (P3), the electron transport capacity decreases while the hole transport capacity increases. Compared to the BTI homopolymer P(BTimR) having an electron mobility of 10(-2) cm(2) V(-1) s(-1), copolymer P1 is ambipolar with balanced hole and electron mobilities of ～10(-4) cm(2) V(-1) s(-1), while P2 and P3 exhibit hole mobilities of ～10(-3) and ～10(-2) cm(2) V(-1) s(-1), respectively. The influence of P(BTimR) homopolymer M(n) on film morphology and device performance was also investigated. The high M(n) batch P(BTimR)-H affords more crystalline film microstructures; hence, 3× increased electron mobility (0.038 cm(2) V(-1) s(-1)) over the low M(n) one P(BTimR)-L (0.011 cm(2) V(-1) s(-1)). In a top-gate/bottom-contact OFET architecture, P(BTimR)-H achieves a high electron mobility of 0.14 cm(2) V(-1) s(-1), only slightly lower than that of state-of-the-art n-type polymer semiconductors. However, the high-lying P(BTimR)-H LUMO results in minimal electron transport on exposure to ambient. Copolymer P3 exhibits a hole mobility approaching 0.1 cm(2) V(-1) s(-1) in top-gate OFETs, comparable to or slightly lower than current state-of-the-art p-type polymer semiconductors (0.1-0.6 cm(2) V(-1) s(-1)). Although BTI building block incorporation does not enable air-stable n-type OFET performance for P(BTimR) or P1, it significantly increases the OFET air stability for p-type P2 and P3. Bottom-gate/top-contact and top-gate/bottom-contact P2 and P3 OFETs exhibit excellent stability in the ambient. Thus, P2 and P3 OFET hole mobilities are almost unchanged after 200 days under ambient, which is attributed to their low-lying HOMOs (>0.2 eV lower than that of P3HT), induced by the strong BTI electron-withdrawing capacity. Complementary inverters were fabricated by inkjet patterning of P(BTimR)-H (n-type) and P3b (p-type).     

Diketopyrrolopyrrole-containing quinoidal small molecules for high-performance, air-stable, and solution-processable n-channel organic field-effect transistors

We report the synthesis, characterization, and application of a novel series of diketopyrrolopyrrole (DPP)-containing quinoidal small molecules as highly efficient n-type organic semiconductors in thin film transistors (TFTs). The first two representatives of these species exhibit maximum electron mobility up to 0.55 cm(2) V(-1) s(-1) with current on/current off (I(on)/I(off)) values of 10(6) for 1 by vapor evaporation, and 0.35 cm(2) V(-1) s(-1) with I(on)/I(off) values of 10(5)-10(6) for 2 by solution process in air, which is the first demonstration of DPP-based small molecules offering only electron transport characteristics in TFT devices. The results indicate that incorporation of a DPP moiety to construct quinoidal architecture is an effective approach to enhance the charge-transport capability.     

Three-chain truxene discotic liquid crystal showing high charged carrier mobility

A new truxene discotic liquid crystal possessing only three octyloxy chains (3C8OTRX) was studied on the mesomorphic and semiconducting properties to reveal that it exhibits a high drift mobility of positive carriers in the order of 10(-2) cm(2) V(-1) s(-1) in the hexagonal ordered columnar (Col(ho)) mesophase.     

Fusion of phosphole and 1,1'-biacenaphthene: phosphorus(V)-containing extended π-systems with high electron affinity and electron mobility

A profusion of phospholes: Diacenaphtho[1,2-b:1',2'-d]phospholes, a new class of arene-fused phosphole π-systems, were synthesized and their structural and electrochemical properties studied. The P-sulfide derivative has a high electron-transporting ability (μ(E) =2.4×10(-3) cm(2) V(-1) s(-1)) in a vacuum-deposited film.     

Internal rotation of methyl group in electronically excited o- and m-ethynyltoluene: new correlation between the Hammett substituent constant σm and rotational barrier change

We have determined the potential-energy function for the internal rotation of the methyl group for o- and m-ethynyltoluene in the electronic excited (S(1)) and ground (S(0)) states by measuring the fluorescence excitation and single-vibronic-level dispersed fluorescence spectra in a jet. The 0-0 bands were observed at 35?444 and 35?416 cm(-1), respectively. The methyl group in o-ethynyltoluene is shown to be a rigid rotor with a potential barrier to rotation of 190 ± 10 cm(-1) in both states. No change in the conformation occurred upon excitation. Barrier heights of m-ethynyltoluene in the S(0) and S(1) states are shown to be 19 ± 3 and 101 ± 1 cm(-1), respectively. A conformational change occurred with rotation by 60[ordinal indicator, masculine] upon excitation. The potential parameters were as follows: reduced rotational constant (B) of 5.323 cm(-1), centrifugal-distortion constant (D) of 6.481 × 10(-5) cm(-1), V(3) = 19 cm(-1), V(6) = -6 cm(-1), and V(9) = 0 cm(-1) in the S(0) state, and B = 5.015 cm(-1), D = 5.392 × 10(-5) cm(-1), V(3) = 101 cm(-1), V(6) = -22 cm(-1), and V(9) = -2 cm(-1) in the S(1) state. For m-methylstyrene, m-tolunitrile, and m-ethynyltoluene, which all have a multiple-bonded carbon in the substituent, we found a new correlation between the Hammett substituent constant σ(m) and the change in the barrier of the methyl group upon excitation.     

Pentacyano-N,N-dimethylaniline in the excited state. Only locally excited state emission, in spite of the large electron affinity of the pentacyanobenzene subgroup

Pentacyano-N,N-dimethylaniline (PCDMA) does not undergo an intramolecular charge transfer (ICT) reaction, even in the strongly polar solvent acetonitrile (MeCN), in clear contrast to 4-(dimethylamino)benzonitrile (DMABN). Within the twisted ICT (TICT) model, this is unexpected, as the electron affinity of the pentacyanobenzene moiety of PCDMA is much larger than that of the benzonitrile subgroup in DMABN. According to the TICT model, the energy of the ICT state of PCDMA would be 2.05 eV (～16550 cm(-1)) lower than that of DMABN, on the basis of the reduction potentials E(A(-)/A) of pentacyanobenzene (-0.29 V vs saturated calomel electrode (SCE)) and benzonitrile (-2.36 V vs SCE), more than enough to compensate for the decrease in energy of the locally excited (LE) state of PCDMA (E(S(1)) = 19990 cm(-1)) relative to that of DMABN (E(S(1)) = 29990 cm(-1)). This absence of a LE → ICT reaction shows that the TICT hypothesis does not hold for PCDMA in the singlet excited state, similar to what was found for DMABN, N-phenylpyrrole, and their derivatives. In this connection, the six dicyano-substituted dimethylanilines are also discussed. The energy gap ΔE(S(1),S(2)) between the two lowest singlet excited states is, at 7170 cm(-1) for PCDMA in MeCN, considerably larger than that for DMABN (2700 cm(-1) in n-hexane, smaller in MeCN). The absence of ICT is therefore in accord with the planar ICT (PICT) model, which considers a sufficiently small ΔE(S(1),S(2)) to be an important condition determining whether an ICT reaction will take place. The fluorescence quantum yield of PCDMA is very small: Φ(LE) = 0.0006 in MeCN at 25 °C, predominantly due to LE → S(0) internal conversion (IC), as the intersystem crossing yield Φ(ISC) is practically zero (<0.01). From the LE fluorescence decay time of 27 ps for PCDMA in MeCN at 25 °C, a radiative rate constant k(f)(LE) = 2 × 10(7) s(-1) results, comparable to the k(f)(LE) of DMABN (6.5 × 10(7) s(-1)) and 2,4,6-tricyano-N,N-dimethylaniline (TCDMA) (1.2 × 10(7) s(-1)) in this solvent, but clearly larger than the k'(f)(ICT) = 0.79 × 10(7) s(-1) of DMABN in MeCN. The IC reaction with PCDMA in MeCN at room temperature, with a rate constant k(IC) of 3.6 × 10(10) s(-1), is much faster than with TCDMA (25 × 10(7) s(-1)) and DMABN (1.3 × 10(7) s(-1), in n-hexane). This is connected with the nonzero (37°) amino twist angle of PCDMA, which leads to a decrease of the effective LE-S(0) energy gap. The femtosecond excited state absorption (ESA) spectra of PCDMA in MeCN at 22 °C are similar to the LE ESA spectra of TCDMA and DMABN and are therefore attributed to the LE state, confirming that an ICT reaction does not occur. The decay of the LE ESA spectra of PCDMA is single exponential, with a decay time of 22 ps, in reasonable agreement with the LE fluorescence decay time of 27 ps at 25 °C. The spectra decay to zero, showing that there is no triplet or other intermediate.     

Continuous beds with vancomycin as chiral stationary phase for capillary electrochromatography

Enantiomeric separations in capillary electrochromatography (CEC) carried out using a continuous-bed chiral stationary phase (CSP) based on the macrocyclic antibiotic, vancomycin, is presented. The continuous beds were prepared from methacryloxypropyl modified fused silica capillaries (100 microm ID) by in situ copolymerization of N-(hydroxymethyl)acrylamide and piperazine diacrylamide with vinyl sulfonic acid comonomer used to introduce ionic functionality and thus a strong electroosmotic flow (EOF). The CSP was subsequently prepared by immobilizing the vancomycin stationary phase by reductive amination. Preliminary results have indicated that an extremely strong EOF is obtained in both the nonaqueous polar organic (15.2 x 10(-5) cm2 V(-1) s(-1) and the aqueous reversed-phase modes of operation (8.5 x 10(-5) cm2 V(-1) s(-1)). Enantioselectivity was obtained for four racemic compounds, the best of which was in the case of thalidomide which was separated in 10 minutes with high resolution (Rs = 2.5) and efficiency (120,000 plates meter(-1)) values.     

Capillary electrochromatography using a fluoropolymer as the chromatographic support material

Fused-silica capillary columns were packed with ethylene chlorotrifluoroethylene (ECTFE) particles for use in capillary electrochromatography (CEC). Electroosmotic flow (EOF) was generated in these columns using acetonitrile-water mixtures as the mobile phase. Electroosmotic mobilities of 1.6 x 10(-4) cm2 V(-1) s(-1) (linear velocities of 1 mm s(-1)) were observed using a mobile phase without an electrolyte present. The EOF in the ECTFE-packed columns is enhanced when using trifluoroacetic acid (TFA) as a mobile phase additive; electroosmotic mobilities of 3.65 x 10(-4) cm2 (V-1) s(-1) (linear velocity of 2.5 mm s(-1)) were observed. This enhancement of EOF is attributed to dynamic coating of the ECTFE particles by TFA. Other electrolytes (i.e., Tris/Tris-HCl buffer and H3PO4) in the mobile phase did not have such an enhancement of EOF. However, a slight enhancement of EOF is observed, for example, if small quantities of TFA are added to the mobile phase containing Tris buffer. The potential of ECTFE for CEC is demonstrated by separating a mixture of amino acids.     

Cation and pressure effects on the electrochemistry of 12-tungstocobaltate and 12-tungstophosphate ions in acidic aqueous solution

The effects of supporting electrolytes and of pressure on the electrode reactions of the aqueous CoW(12)O(40)(5-/6-) couple at 25 degrees C are reported, together with limited data on PW(12)O(40)(3-)/4-) and PW(12)O(40)(4-/5-). The half-wave potentials E(1/2) for the CoW(12) couple become moderately more positive with increasing electrolyte concentration and cationic charge, and also in the sequences Li(+) approximately Na(+) < NH(4)(+) < or = H(+) < K(+) < Rb(+) < Cs(+) and Na(+) < Mg(2+) < Ca(2+) < Eu(3+). The mean diffusion coefficients for CoW(12) with the 1:1 electrolytes are independent of electrolyte concentration and rise only slightly from Li(+) to Cs(+), averaging (2.4 +/- 0.3) x 10(-6) cm(2) s(-1). Neither the volumes of activation for diffusion Delta V(diff)(++) (average -0.9 +/- 1.1 cm(3) mol(-1)) nor the electrochemical cell reaction volumes Delta V(Ag/AgCl) (average -22 +/- 2 cm(3) mol(-1)) for the CoW(12) couple show significant dependence on electrolyte identity or concentration. For the PW(12)(3-/4-) and PW(12)(4-/5-) couples, Delta V(Ag/AgCl) = -14 and -26 cm(3) mol(-1), respectively, suggesting a dependence on Delta(z(2)) (z = ionic charge number) as predicted by the Born-Drude-Nernst theory of electrostriction of solvent, but comparison with Delta V(Ag/AgCl) for CoW(12) and other anion-anion couples shows that the Born-Drude-Nernst approach fails in this context. For aqueous electrode reactions of CoW(12), as for other anionic couples such as cyanometalates, the standard rate constants k(el) show specific cation catalysis (Na(+) < K(+) < Rb(+) < Cs(+)), and Delta V(el++) is invariably positive, in the presence of supporting electrolytes. For the heavier group 1 cations, Delta V(el++) is particularly large (10-15 cm(3) mol(-1)), consistent with a partial dehydration of the cation to facilitate catalysis of the electron-transfer process. The positive values of Delta V(el++) for the CoW(12) couple cannot be attributed to rate control by solvent dynamics, which would lead to Delta V(el++) < or = Delta V(diff++), i.e., to negative or zero Delta V(el++) values. These results stand in sharp contrast to those for aqueous cationic couples, for which k(el) shows relatively little influence of the nature of the counterion and Delta V(el++) is always negative.     

Aceno[2,1,3]thiadiazoles for field-effect transistors: synthesis and crystal packing

An efficient synthetic approach to a series of aceno[2,1,3]thiadiazole derivatives is described. 2-TIPS and 2-TES molecules exhibited different crystal packings, and 2-TIPS show good device performances with hole mobility up to 0.4 cm(2) V(-1) s(-1) and an average mobility of 0.15 cm(2) V(-1) s(-1) as the active material for organic field-effect transistors. All of the results demonstrate these aceno[2,1,3]thiadiazole derivatives as promising materials for optoelectronic devices.     

Synthesis and characterization of dithienylbenzobis(thiadiazole)-based low band-gap polymers for organic electronics

New donor-acceptor alternating conjugated polymers were synthesized and characterized. Among them, PCPBBT exhibited a band-gap of 1.01 eV and ambipolar characteristics with μ(h) = 7.1 × 10(-4) cm(2) V(-1) s(-1) and μ(e) = 3.3 × 10(-3) cm(2) V(-1) s(-1).     

A laccase-wiring redox hydrogel for efficient catalysis of O2 electroreduction

Laccase was earlier wired to yield an O2 electroreduction catalyst greatly outperforming platinum and its alloys. Here we describe the design, synthesis optimization of the composition, and characterization of the +0.55 V (AgAgCl) laccase-wiring redox hydrogel, with an apparent electron diffusion coefficient (D(app)) of 7.6 x 10(-7) cm2 s(-1). The high D(app) results in the tethering of redox centers to the polymer backbone through eight-atom-long spacer arms, which facilitate collisional electron transfer between proximal redox centers. The O2 flux-limited, true-area-based current density was increased from the earlier reported 560 to 860 microA cm(-2). When the O2 diffusion to the 7-microm-diameter carbon fiber cathode was cylindrical, half of the O2 flux-limited current was reached already at 0.62 V and 90% at 0.56 V vs Ag/AgCl, merely -0.08 and -0.14 V versus the 0.7 V (Ag/AgCl) reversible O2/H2O half-cell potential at pH 5.     

Infrared spectroscopic study of the carbon dioxide adsorption on the surface of Ga2O3 polymorphs

The adsorption of CO(2) over a set of gallium (III) oxide polymorphs with different crystallographic phases (alpha, beta, and gamma) and surface areas (12-105 m(2) g(-1)) was studied by in situ infrared spectroscopy. On the bare surface of the activated gallias (i.e., partially dehydroxylated under O(2) and D(2) (H(2)) at 723 K), several IR signals of the O-D (O-H) stretching mode were assigned to mono-, di- and tricoordinated OD (OH) groups bonded to gallium cations in tetrahedral and/or octahedral positions. After exposing the surface of the polymorphs to CO(2) at 323 K, a variety of (bi)carbonate species emerged. The more basic hydroxyl groups were able to react with CO(2), to yield two types of bicarbonate species: mono- (m-) and bidentate (b-) [nu(as)(CO(3)) = 1630 cm(-1); nu(s)(CO(3)) = 1431 or 1455 cm(-1) (for m- or b-); delta(OH) = 1225 cm(-1)]. Together with the bicarbonate groups, IR bands assigned to carboxylate [nu(as)(CO(2)) = 1750 cm(-1); nu(s)(CO(2)) = 1170 cm(-1)], bridge carbonate [nu(as)(CO(3)) = 1680 cm(-1); nu(s)(CO(3)) = 1280 cm(-1)], bidentate carbonate [nu(as)(CO(3)) = 1587 cm(-1); nu(s)(CO(3)) = 1325 cm(-1)], and polydentate carbonate [nu(as)(CO(3)) = 1460 cm(-1); nu(s)(CO(3)) = 1406 cm(-1)] species developed, up to approximately 600 Torr of CO(2). However, only the bi- and polydentate carbonate groups still remained on the surface upon outgassing the samples at 323 K. The total amount of adsorbed CO(2), measured by volumetric adsorption (323 K), was approximately 2.0 micromol m(-2) over any of the polymorphs, congruent with an integrated absorbance of (bi)carbonate species proportional to the surface area of the materials. Upon heating under flowing CO(2) (760 Torr), most of the (bi)carbonate species vanished a T > 550 K, but polydentate groups remained on the surface up to the highest temperature used (723 K). A thorough discussion of the more probable surface sites involved in the adsorption of CO(2) is made.