Pyrenoimidazole‐Based Deep‐Blue‐Emitting Materials: Optical,Electrochemical, and Electroluminescent Characteristics

A series of pyrenoimidazoles that contained various functional chromophores, such as anthracene, pyrene, triphenylamine, carbazole, and fluorene, were synthesized and characterized by optical, electrochemical, and theoretical studies. The absorption spectra of the dyes are dominated by electronic transitions that arise from the pyrenoimidazole core and the additional chromophore. All of the dyes exhibited blue‐light photoluminescence with moderate‐to‐high quantum efficiencies. They also displayed high thermal stability and their thermal‐decomposition temperatures fell within the range 462–512 °C; the highest decomposition temperature was recorded for a carbazole‐containing dye. The oxidation propensity of the dyes increased on the introduction of electron‐rich chromophores, such as triphenylamine or carbazole. The application of selected dyes that featured additional chromophores such as pyrene, carbazole, and triphenylamine as blue‐emissive dopants into multilayered organic light‐emitting diodes with a 4,4′‐bis(9H‐carbazol‐9‐yl)biphenyl (CBP) host was investigated. Devices that were based on triphenylamine‐ and carbazole‐containing dyes exhibited deep‐blue emission (CIE 0.157, 0.054 and 0.163, 0.041), whereas a device that was based on a pyrene‐containing dye showed a bright‐blue emission (CIE 0.156, 0.135).     

TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC

Self-made TiO₂ nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO₂ thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO₂ thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO₂ nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO₂ thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO₂ film presents excellent dye absorption performance and even doesn't need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell.     

Kinetics and Mechanism of the Cerium(IV) Oxidation of Arnold's Base and the Protonation and Hydroxylation of Michler's Hydrol Blue

In aqueous H₂SO₄, Ce(IV) ion oxidizes rapidly Arnold's base((p-Me₂NC₆H₄)₂CH₂, Ar₂CH₂) to the protonated species of Michler's hydrol((p-Me₂NC₆H₄)₂CHOH, Ar₂CHOH) and Michler's hydrol blue((p-Me₂NC₆H₄)₂CH⁺, Ar₂CH⁺). With Ar₂CH₂ in excess, the rate law of the Ce(IV)-Ar₂CH₂ reaction in 0.100 M H₂SO₄ is expressed -d[Ce(IV)]/dt = k_app[Ar₂CH₂]₀[Ce(IV)] with k_app = 199 ± 8M^?1s^?1 at25°C. When the consumption of Ce(IV) ion is nearly complete, the characteristic blue color of Ar₂CH⁺ ion starts to appear; later it fades relatively slowly. The electron transfer of this reaction takes place on the nitrogen atom rather than on the methylene carbon atom. The dissociation of the binuclear complex [Ce(III)ArCHAr-Ce(III)] is responsible for the appearance of the Ar₂CH⁺ dye whereas the protonation reaction causes the dye to fade. In highly acidic solution, the rate law of the protonation reaction of Michler's hydrol blue is -d[Ar₂CH⁺]/dt = k_obs[Ar₂CH⁺] where K_obs = ((ac + 1)[H*] + bc[H⁺]²)/(a + b[H⁺]) (in HClO₄) and k_obs= ((ac + 1 + e[HSO₄^?])[H⁺] + bc[H⁺]² + d[HSO₄^?] + q[HSO₄^?]²/[H⁺])/(a + b[H⁺] + f[HSO₄^?] + g[HSO₄^?]/[H⁺]) (in H₂SO₄), and at 25°C and μ = 0.1 M, a = 0.0870 M s, b = 0.655 s, c = 0.202 M^?1s^?1, d = 0.110, e = 0.0070 M^?1, f = 0.156 s, g = 0.156 s, and q = 0.124. In highly basic solution, the rate law of the hydroxylation reaction of Michler's hydrol blue is -d[Ar₂CH⁺]/dt = k_OH[OH^?]₀[Ar₂CH⁺] with k_OH = 174 ± 1 M^?1s^?1 at 25°C and μ = 0.1 M. The protonation reaction of Michler's hydrol blue takes place predominantly via hydrolysis whereas its hydroxylation occurs predominantly via the path of direct OH attack.     

Kinetic Study of the Bromine-Catalyzed Isomerization of Methyl- and Chloro-Maleic Acids in Aqueous Ce(IV)-Br -H2SO4 Medium

Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br^?₂ · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br^?₂ · ? MSA+Br^?₂ · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br^?₂ · ? MSA+Br^?₂ · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO₂H=CR'CO₂H) in aqueous solution.     

Kinetic Study of the Isotope Exchange Reactions of Malonic Acid and Malonate Ion Using 1H NMR Spectroscopy. Inhibition of Acid and Base

The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D₂O solutions, respectively, using ¹H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO₃ (0–3 M) and DSO₄^? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO₄^? ion (> 0.2 M), D₃PO₄, D₂PO₄^? ion or DPO₄^2– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D₂O is DPO₄^2– > D₂PO₄^? > D₃PO₄ > DSO₄^? > DNO₃. The rate of the isotope exchange reaction of malonate ion in D₂O decreases to a minimum and then increases with increased [NaOD]₀. The mechanism of the isotope exchange reaction of malonic acid in acidic D₂O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system.     

Inverse phase transfer catalysis. Kinetics of the pyridine 1-oxide-catalyzed reactions of dichlorobenzoyl chlorides and benzoate ions

The substitution reactions of 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoyl chloride (Cl₂C₆H₃COCl) and 2,3-, 2,4-, 3,4-, or 3,5-dichlorobenzoate ion (Cl₂C₆H₅COO⁻) or benzoate ion (C₆H₅COO⁻) in a two-phase H₂O/CH₂Cl₂ medium using pyridine 1-oxide (PNO) as an inverse phase transfer catalyst were investigated. The reaction of Cl₂C₆H₃COCl and PNO in CH₂Cl₂ to produce the ionic intermediate, 1-(dichlorobenzoyloxy)-pyridinium chloride (Cl₂C₆H₃COONP⁺Cl⁻) is the rate-determining step. In the PNO-catalyzed two-phase reaction of Cl₂C₆H₃COCl and C₆H₅COONa, the order of reactivities of Cl₂C₆H₃COCl toward reaction with PNO is (2,3-, 2,4-)>3,5->3,4-2,6-Cl₂C₆H₃COCl, whereas it is 3,5->(2,3-, 3,4-)>2,4-Cl₂C₆H₃COCl in the PNO-catalyzed two-phase reaction of Cl₂C₆H₃COCl and the corresponding Cl₂C₆H₃COONa. The order of reactivities of Cl₂C₆H₃COO⁻ ions towards the reaction with 1-(benzoyloxy)-pyridinium (C₆H₅COONP⁺) ion is (3,4-, 3,5-)>(2,3-, 2,4-Cl₂C₆H₃COO⁻).     

Inverse phase transfer catalysis: kinetics of the pyridine-1-oxide-catalyzed two-phase reactions of methyl-, methoxy-, iodo-, and nitro-benzoyl chlorides and benzoate ions

The substitution reactions of XC₆H₄COCl [X=2-, 3-, or 4-CH₃; 2-, 3-, or 4-CH₃O; 2-, or 4-I; or 2-, 3-, or 4-NO₂] and YC₆H₄COONa [Y=2-, 3-, or 4-CH₃; 2-, 3-, or 4-CH₃O; 2-I; 4-NO₂; or H] in a two-phase H₂O/CH₂Cl₂ medium using pyridine-1-oxide (PNO) as an inverse phase transfer catalyst were investigated. In general, the kinetics of the reaction follows a pseudo-first-order rate law, with the observed rate constant being a linear function of the concentration of PNO in the water phase. In contrast to other analogous reactions, the hydrolysis reaction of 2-, 3-, or 4-NO₂C₆H₄COCl in H₂O/CH₂Cl₂ medium is catalyzed considerably by PNO and reaches an equilibrium. In the PNO-catalyzed reaction of XC₆H₄COCl and XC₆H₄COONa in H₂O/CH₂Cl₂ medium, the order of reactivities of XC₆H₄COCl toward reaction with PNO in CH₂Cl₂ is 2-IC₆H₄COCl>4-IC₆H₄COCl>(C₆H₅COCl,3-CH₃OC₆H₄COCl)>3-CH₃C₆H₄COCl>(2-CH₃C₆H₄COCl,4-CH₃C₆H₄COCl)>4-CH₃OC₆H₄COCl>2-CH₃OC₆H₄COCl. Combined with the results of other analogous reactions, good Hammett correlations with positive reaction constant were obtained for the meta- and para-substituents, which supports that the XC₆H₄COCl–PNO reaction in CH₂Cl₂ is a nucleophilic substitution reaction.     

Magnetic levitation of YBa2Cu3Oy single crystals

By using an ordinary electric balance, we are able to measure the magnetic levitation forces acting on a superconducting YBa₂Cu₃O_y (YBCO) single crystal. It is found that when the external magnetic field is parallel to the c-axis of the single crystal, the hysteretic levitation curve is similar to that of a melt-processed YBCO superconducting sample. However, when the external magnetic field is perpendicular to the c-axis of the YBCO single crystal, the levitation forces are too small to be measured by our equipment. Also, we have introduced a simple model with the Bean's approximations to explain the levitation forces. The critical current density derived from this model by fitting with experimental data is quite close to the value obtained from magnetization measurements.     

Isomerization of Maleic Acid to Fumaric Acid Catalyzed by Bromate Ion and Bromine

In the presence of a relatively small amount of bromate, maleic acid in aqueous sulfuric acid isomerizes catalytically to fumaric acid in the dark at room temperature. The concomitant presence of a suitable amount of bromine in CCI, phase raises the rate and yield significantly. The yield and rate of isomerization depend on the relative amounts of maleic acid, bromate, bromine, and sulfuric acid. For a favorable condition, nearly 90% yield can be obtained. Raising the temperature accelerates the production of fumaric acid while decreases the final yield. The isomerization reaction competes favorably with the redox reaction at room temperature while the latter dominates at high temperature. For the heterogeneous case, the agitation of the reaction mixture delays the isomerization. The presence of cumene or benzene inhibits the isomerization. Hypobromous acid is proposed to play a major role in catalyzing the isomerization. A mechanism is proposed to rationalize the experimental results.