Studies on Intra‐Supramolecular and Intermolecular Electron‐Transfer Processes between Zinc Naphthalocyanine and Imidazole‐Appended Fullerene

Spectroscopic, computational, redox, and photochemical behavior of a self‐assembled donor‐acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2‐(4′‐imidazolylphenyl)fulleropyrrolidine, C₆₀Im) was investigated in noncoordinating solvents, toluene and o‐dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3–21G(*) computational studies revealed self‐assembled supramolecular 1:1 dyad formation between the ZnNc and C₆₀Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one‐electron redox processes in o‐dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited‐state electron‐transfer processes were monitored by both optical‐emission and transient‐absorption techniques. Direct evidence for the radical‐ion‐pair (C₆₀Im^.?:ZnNc ^{. +} ) formation was obtained from picosecond transient‐absorption spectral studies, which indicated charge separation from the singlet‐excited ZnNc to the C₆₀Im moiety. The calculated rates of charge separation and charge recombination were 1.4×10¹⁰ s^?1 and 5.3×10⁷ s^?1 in toluene and 8.9×10⁹ s^?1 and 9.2×10⁷ s^?1 in o‐dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C₆₀Im occurs and the second‐order rate constant (k_q^triplet) for this quenching process was 5.3×10⁸ M ^?1 s^?1.     

Light harvesting zinc naphthalocyanine-perylenediimide supramolecular dyads: long-lived charge-separated states in nonpolar media

Photoinduced electron-transfer dynamics of self-assembled donor-acceptor dyads formed by axial coordination of zinc naphthalocyanine, ZnNc, and perylenediimide (PDI) bearing either pyridine (py) or imidazole (im) coordinating ligands were investigated. The PDIim unit was functionalized with tert-octylphenoxy groups at the bay positions, which avoid aggregation providing solubility, to examine the effect of the bulky substituents at the bay positions on the rates of electron-transfer reactions. The combination between zinc naphthalocyanine and perylenediimide entities absorbs light over a wide region of the visible and near infrared (NIR) spectrum. The binding constants of the self-assembled ZnNc:PDIpy (1) and ZnNc:PDIim (2) in toluene were found to be 2.40 × 10(4) and 1.10 × 10(5) M(-1), respectively, from the steady-state absorption and emission measurements, indicating formation of moderately stable complexes. The geometric and electronic calculations by using an ab initio B3LYP/6-311G method showed the majority of the highest occupied frontier molecular orbital (HOMO) on the zinc naphthalocyanine entity, while the lowest unoccupied molecular orbital (LUMO) was on the perylenediimide entities, suggesting that the charge-separated states of the supramolecular dyads are ZnNc˙(+):PDI˙(-). The electrochemical results suggest the exothermic charge-separation process via the singlet states of both ZnNc and PDI entities in nonpolar toluene. Upon coordination of perylenediimide to ZnNc, the main quenching pathway involved charge separation via the singlet-excited states of ZnNc and PDIs. Clear evidence of the intramolecular electron transfer from the singlet-excited state of ZnNc to PDI within the supramolecular dyads in toluene was monitored by the femtosecond laser photolysis by observing the characteristic absorption band of the PDI radical anion (PDI˙(-)) and the ZnNc radical cation (ZnNc˙(+)) in the visible and NIR regions. The rate constants of charge-separation (k(CS)) processes of the self-assembled dyads 1 and 2 were determined to be 4.05 × 10(10) and 1.20 × 10(9) s(-1), respectively. The rate constant of charge recombination (k(CR)) and the lifetime of charge-separated states (τ(CS)) of dyad 1 were determined to be 2.34 × 10(8) s(-1) and 4.30 ns, respectively. Interestingly, a slower charge recombination (2.20 × 10(7) s(-1)) and a longer lifetime of the charge separated state (45 ns) were observed in dyad 2 in nonpolar toluene by utilizing the nanosecond transient measurements. The absorption in a wide section of the solar spectrum and the high charge-separation/charge-recombination ratio suggest the usefulness of the self-assembled zinc naphthalocyanine-perylenediimide dyads as good photosynthetic models.     

Two‐Step direct arylation for synthesis of naphthalenediimide‐based conjugated polymer

A naphthalenediimide (NDI)‐based conjugated polymer was synthesized by a two‐step direct C‐H arylation sequence. In the first step, two ethylenedioxythiophene units were coupled to NDI by direct arylation. In the second step, the direct arylation polycondensation of the monomer, formed in the first step, with 2,7‐dibromo‐9,9‐dioctylfluorene afforded the corresponding NDI‐based conjugated polymer ( PEDOTNDIF ) with molecular weight of 21,500 in 91% yield. The optical and electrochemical properties of the polymer were evaluated. The polymer showed ambipolar behavior in organic field‐effect transistors (OFETs). The electron mobility of PEDOTNDIF was estimated to be 2.3 × 10^?6 cm² V^?1 s^?1 using an OFET device with source‐drain (S‐D) Au electrodes. A modified OFET device with S‐D MgAg electrodes increased the electron mobility for PEDOTNDIF to 1.0 × 10^?5 cm² V^?1 s^?1 due to the more suitable work function of these electrodes, which reduced the injection barrier to the semiconducting polymer. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1401–1407     

Supramolecular Tetrad Featuring Covalently Linked Bis(porphyrin)–Phthalocyanine Coordinated to Fullerene: Construction and Photochemical Studies

A multimodular donor–acceptor tetrad featuring a bis(zinc porphyrin)–(zinc phthalocyanine) ((ZnP–ZnP)–ZnPc) triad and bis‐pyridine‐functionalized fullerene was assembled by a “two‐point” binding strategy, and investigated as a charge‐separating photosynthetic antenna‐reaction center mimic. The spectral and computational studies suggested that the mode of binding of the bis‐pyridine‐functionalized fullerene involves either one of the zinc porphyrin and zinc phthalocyanine (Pc) entities of the triad or both zinc porphyrin entities leaving ZnPc unbound. The binding constant evaluated by constructing a Benesi–Hildebrand plot by using the optical data was found to be 1.17×10⁵ M ^?1, whereas a plot of “mole‐ratio” method revealed a 1:1 stoichiometry for the supramolecular tetrad. The mode of binding was further supported by differential pulse voltammetry studies, in which redox modulation of both zinc porphyrin and zinc phthalocyanine entities was observed. The geometry of the tetrad was deduced by B3LYP/6‐31G* optimization, whereas the energy levels for different photochemical events was established by using data from the optical absorption and emission, and electrochemical studies. Excitation of the zinc porphyrin entity of the triad and tetrad revealed ultrafast singlet–singlet energy transfer to the appended zinc phthalocyanine. The estimated rate of energy transfer (k_ENT) in the case of the triad was found to be 7.5×10¹¹ s^?1 in toluene and 6.3×10¹¹ s^?1 in o‐dichlorobenzene, respectively. As was predicted from the energy levels, photoinduced electron transfer from the energy‐transfer product, that is, singlet‐excited zinc phthalocyanine to fullerene was verified from the femtosecond‐transient spectral studies, both in o‐dichlorobenzene and toluene. Transient bands corresponding to ZnPc ^{? +} in the 850 nm range and C₆₀ ^{? ?} in the 1020 nm range were clearly observed. The rate of charge separation, k_CS, and rate of charge recombination, k_CR, for the (ZnP–ZnP)–ZnPc ^{? +}:Py₂C₆₀ ^{? ?} radical ion pair (from the time profile of 849 nm peak) were found to be 2.20×10¹¹ and 6.10×10⁸ s^?1 in toluene, and 6.82×10¹¹ and 1.20×10⁹ s^?1 in o‐dichlorobenzene, respectively. These results revealed efficient energy transfer followed by charge separation in the newly assembled supramolecular tetrad.     

Tetrathiafulvalene‐Fused Porphyrins via Quinoxaline Linkers: Symmetric and Asymmetric Donor–Acceptor Systems

A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric P–TTF–P triads 1 a – c and asymmetric P–TTF dyads 2 a , b in good yields. These planar and extended π‐conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge‐transfer excitations within the donor–acceptor assemblies. Quantum‐chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited‐state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2 a , b but not in triads 1 a – c . Clear evidence for a photoinduced and relatively long lived charge‐separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnP–TTF dyad and a pyridine‐functionalized C₆₀ acceptor unit. This specific excited state results in a (ZnP–TTF)^?+ ??? (C₆₀py)^?? state. The binding constant of Zn^II ??? py is evaluated by constructing a Benesi–Hildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20×10⁴ M ^?1, which is remarkably high for bonding of pyridine to ZnP.     

Efficient Electrocatalytic Detection of Epinephrine at Gold Electrodes Modified with Self‐Assembled Metallo‐Octacarboxyphthalocyanine Complexes

Electrocatalysis of epinephrine at gold electrode pre‐modified with the self‐assembled monolayer of cysteamine and subsequently integrated with novel metallo‐octacarboxyphthalocyanine (MOCPc where M=Fe, Co and Mn) complexes (Au‐Cys‐MOCPc) was investigated. The electrodes showed response to the presence of epinephrine. The oxidation peak potential (E_p/V vs. Ag|AgCl, sat'd KCl) and charge transfer resistance (R_ct (kΩ)) in epinephrine solution depend markedly on the central metal of the phthalocyanine cores: Au‐Cys‐FeOCPck_ch=4.1×10⁷ M^?1 s^?1) which is higher than that of the Au‐cys‐CoOCPc or Au‐cys‐MnOCPc electrode. Mechanism, recognizing the mediation of the electrocatalytic process by the central M(II)/M(III) redox processes was proposed. Epinephrine electro‐oxidation at the Au‐cys‐FeOCPc electrode was studied in more details for the response characteristics. The diffusion coefficient of epinephrine was evaluated as (2.62±0.23)×10^?9 cm² s^?1. It was established that Au‐Cys‐FeOCPc is suitable for sensitive determination of epinephrine in physiological pH (7.40) conditions showing linear concentration range of up to 300 nM, with excellent sensitivity (0.53±0.01 nA nM^?1), and very low limits of detection (13.8 nM) and quantification (45.8 nM). The peak separation between ascorbic acid and epinephrine is large enough (190 mV) to permit simultaneous determination of both epinephrine and ascorbic acid in physiological pH 7.4 conditions using the Au‐cys‐FeOCPc electrode. Au‐cys‐FeOCPc electrode was successfully used for the determination of epinephrine in epinephrine hydrochloric acid injection with recovery of ca. 98.4%.     

Through bond mechanism versus exciplex formation in the photochemistry of fullerene / ferrocene donor-bridge-acceptor dyads

A systematic fluorescence and flash photolytic investigation of a series of covalently linked fullerene / ferrocene based donor-bridge-acceptor dyads is reported as a function of the nature of the bridge between the donor site and acceptor site. The fluorescence of the investigated dyads 2 (Φ_rel = 0.17 × 10^?4, 3 (Φ_rel = 0.78 × 10^?4), 4 (Φ_rel = 1.5 × 10^?4), 5 (Φ_rel = 0.7 × 10^?4), and 6 (Φ_rel = 2.9 × 10^?4) were substantially quenched, relative to N-methyl fulleropyrrolidine (1) (Φ_rel = 6.0 × 10^?4). Photolysis of N-methyl fulleropyrrolidine (1) in toluene revealed formation of the excited singlet state which was followed by a rapid intersystem crossing to the excited triplet state. On the other hand, the fate of the excited singlet state of 2, 3, 4, 5, and 6 was found to be governed by rapid intramolecular quenching, with rate constants of 28×10⁹ s^?1, 6.9×10⁹ s^?1, and 3.4×10⁹ s^?1, 14×10⁹ s^?1, 2.3×10⁹ s^?1 respectively. The electron transfer process and the charge separation were confirmed by monitoring the characteristic π-radical anion bands at λ_max = 400 and 1055 nm in degassed benzonitrile with τ_1/2 = 1.8 μs (3) and 2.5 μs (4).     

Nanostructured Cobalt(II) Tetracarboxyphthalocyanine Complex Supported Within the MWCNT Frameworks: Electron Transport and Charge Storage Capabilities

The electrochemical redox properties of a surface‐confined thin solid film of nanostructured cobalt(II) tetracarboxyphthalocyanine integrated with multiwalled carbon nanotube (nanoCoTCPc/MWCNT) have been investigated. This novel nanoCoTCPc/MWCNT material was characterized using SEM, TEM, zeta analysis and electrochemical methods. The nanoCoTCPc/MWCNT nanohybrid material exhibited an extra‐ordinarily high conductivity (15 mS cm^?1), which is more than an order of magnitude greater than that of the MWCNT‐SO₃H (527 µS cm^?1) and three orders of a magnitude greater than the nanoCoTCPc (4.33 µS cm^?1). The heterogeneous electron transfer rate constant decreases as follows: nanoCoTCPc/MWCNT (k_app≈19.73×10^?3 cm s^?1)>MWCNT‐SO₃H (k_app≈11.63×10^?3 cm s^?1)>nanoCoTCPc (k_app≈1.09×10^?3 cm s^?1). The energy‐storage capability was typical of pseudocapacitive behaviour; at a current density of 10 µA cm^?2, the pseudocapacitance decreases as nanoCoTCPc/MWCNT (3.71×10^?4 F cm^?2)>nanoCoTCPc (2.57×10^?4 F cm^?2)>MWCNT‐SO₃H (2.28×10^?4 F cm^?2). The new nanoCoTCPc/MWCNT nanohybrid material promises to serve as a potential material for the fabrication of thin film electrocatalysts or energy‐storage devices.     

Supramolecular Formation of Li+@PCBM Fullerene with Sulfonated Porphyrins and Long‐Lived Charge Separation

Lithium‐ion‐encapsulated [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester fullerene (Li⁺@PCBM) was utilized to construct supramolecules with sulfonated meso‐tetraphenylporphyrins (MTPPS^4?; M=Zn, H₂) in polar benzonitrile. The association constants were determined to be 1.8×10⁵ M ^?1 for ZnTPPS^4?/Li⁺@PCBM and 6.2×10⁴ M ^?1 for H₂TPPS^4?/Li⁺@PCBM. From the electrochemical analyses, the energies of the charge‐separated (CS) states were estimated to be 0.69 eV for ZnTPPS^4?/Li⁺@PCBM and 1.00 eV for H₂TPPS^4?/Li⁺@PCBM. Upon photoexcitation of the porphyrin moieties of MTPPS^4?/Li⁺@PCBM, photoinduced electron transfer occurred to produce the CS states. The lifetimes of the CS states were 560 μs for ZnTPPS^4?/Li⁺@PCBM and 450 μs for H₂TPPS^4?/Li⁺@PCBM. The spin states of the CS states were determined to be triplet by electron paramagnetic resonance spectroscopy measurements at 4 K. The reorganization energies (λ) and electronic coupling term (V) for back electron transfer (BET) were determined from the temperature dependence of k_BET to be λ=0.36 eV and V=8.5×10^?3 cm^?1 for ZnTPPS^4?/Li⁺@PCBM and λ=0.62 eV and V=7.9×10^?3 cm^?1 for H₂TPPS^4?/Li⁺@PCBM based on the Marcus theory of nonadiabatic electron transfer. Such small V values are the result of a small orbital interaction between the MTPPS^4? and Li⁺@PCBM moieties. These small V values and spin‐forbidden charge recombination afford a long‐lived CS state.     

Gas‐phase ozonolysis: Rate coefficients for a series of terpenes and rate coefficients and OH yields for 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene

The kinetics of the gas‐phase reactions of O₃ with a series of selected terpenes has been investigated under flow‐tube conditions at a pressure of 100 mbar synthetic air at 295 ± 0.5 K. In the presence of a large excess of m‐xylene as an OH radical scavenger, rate coefficients k(O₃+terpene) were obtained with a relative rate technique, (unit: cm³ molecule^?1 s^?1, errors represent 2σ): α‐pinene: (1.1 ± 0.2) × 10^?16, ³Δ‐carene: (5.9 ± 1.0) × 10^?17, limonene: (2.5 ± 0.3) × 10^?16, myrcene: (4.8 ± 0.6) × 10^?16, trans‐ocimene: (5.5 ± 0.8) × 10^?16, terpinolene: (1.6 ± 0.4) × 10^?15 and α‐terpinene: (1.5 ± 0.4) × 10^?14. Absolute rate coefficients for the reaction of O₃ with the used reference substances (2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene) were measured in a stopped‐flow system at a pressure of 500 mbar synthetic air at 295 ± 2 K using FT‐IR spectroscopy, (unit: cm³ molecule^?1 s^?1, errors represent 2σ ): 2‐methyl‐2‐butene: (4.1 ± 0.5) × 10^?16 and 2,3‐dimethyl‐2‐butene: (1.0 ± 0.2) × 10^?15. In addition, OH radical yields were found to be 0.47 ± 0.04 for 2‐methyl‐2‐butene and 0.77 ± 0.04 for 2,3‐dimethyl‐2‐butene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 394–403, 2002     

Rate coefficients for CS reactions with O2, O3 and NO2 AT 298 K

CS radicals have been produced by photodissociation of CS₂ at 193 nm and their disappearance monitored by LIF. The vibrationally excited CS radicals rapidly relax to CS(ν = 0). At 298 K, the rate coefficients for CS(ν = 0) reactions with O₂, O₃ and NO₂ are (2.9 ± 0.4) × 10_?19, (3.0 ± 0.4) × 10^?16 and (7.6 ± 1.1) × 10^?17 cm³ molecule^?1 s^?1 respectively. The quenching of CS(A ¹II)_ν=0 by He has a rate coefficient of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1.     

Ultrafast Photoinduced Energy and Electron Transfer in Multi‐Modular Donor–Acceptor Conjugates

New multi‐modular donor–acceptor conjugates featuring zinc porphyrin (ZnP), catechol‐chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C₆₀), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction‐center mimics. The X‐ray structure of triphenylamine‐BDP is also reported. The wide‐band capturing polyad revealed ultrafast energy‐transfer (k_ENT=1.0×10¹² s^?1) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA‐BDP‐ZnP triad through metal–ligand axial coordination resulted in electron donor–acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron‐transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion‐pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non‐polar toluene were in the range of 5.0×10⁹–3.5×10¹⁰ s^?1. Stabilization of the charge‐separated state in these multi‐modular donor–acceptor polyads is also observed to certain level.     

Preparation and characterization of conductive chitosan–ionic liquid composite membranes

Anhydrous conductive membranes composing of a composite of chitosan (CS) and ionic liquids with symmetrical carboxyl groups were explored. Scanning electron microscope images revealed that porous composite membranes could be obtained by combining CS with different amounts of 1,4‐bis(3‐carboxymethyl‐imidazolium)‐1‐yl butane chloride ([CBIm]Cl). Fourier transform infrared and proton nuclear magnetic resonance confirmed that the formation of ammonium salts after CS was combined with [CBIm]Cl. The thermal property of CS–ionic liquid composite membranes was studied through thermogravimetric analysis. The anhydrous ionic conductivities of CS–[CBIm]X (X = Cl, Ac, BF₄, and I) composite membranes were measured using ac impedance spectroscopy at room temperature in N₂ atmosphere. The conductivities (0.4–0.7 × 10^?4 Scm^?1), found to be in the same range as semiconductors, were significantly higher than those of pure CS membrane (<10^?8 Scm^?1). In addition, the anhydrous conductivity of composite membrane based on CS–[CBIm]I at room temperature reached a level as high as 0.91 × 10^?2 Scm^?1 when iodine was doped. Copyright © 2011 John Wiley & Sons, Ltd.     

Binding of Scandium Ions to Metalloporphyrin–Flavin Complexes for Long‐Lived Charge Separation

A porphyrin–flavin‐linked dyad and its zinc and palladium complexes (MPor?Fl: 2 ?M, M=2 H, Zn, and Pd) were newly synthesized and the X‐ray crystal structure of 2 ?Pd was determined. The photodynamics of 2 ?M were examined by femto‐ and nanosecond laser flash photolysis measurements. Photoinduced electron transfer (ET) in 2 ?H₂ occurred from the singlet excited state of the porphyrin moiety (H₂Por) to the flavin (Fl) moiety to produce the singlet charge‐separated (CS) state ¹(H₂Por^.+?Fl^.?), which decayed through back ET (BET) to form ³[H₂Por]*?Fl with rate constants of 1.2×10¹⁰ and 1.2×10⁹ s^?1, respectively. Similarly, photoinduced ET in 2 ?Pd afforded the singlet CS state, which decayed through BET to form ³[PdPor]*?Fl with rate constants of 2.1×10¹¹ and 6.0×10¹⁰ s^?1, respectively. The rate constant of photoinduced ET and BET of 2 ?M were related to the ET and BET driving forces by using the Marcus theory of ET. One and two Sc³⁺ ions bind to the flavin moiety to form the Fl?Sc³⁺ and Fl?(Sc³⁺)₂ complexes with binding constants of K₁=2.2×10⁵ M ^?1 and K₂=1.8×10³ M ^?1, respectively. Other metal ions, such as Y³⁺, Zn²⁺, and Mg²⁺, form only 1:1 complexes with flavin. In contrast to 2 ?M and the 1:1 complexes with metal ions, which afforded the short‐lived singlet CS state, photoinduced ET in 2 ?Pd???Sc³⁺ complexes afforded the triplet CS state (³[PdPor^.+?Fl^.??(Sc³⁺)₂]), which exhibited a remarkably long lifetime of τ=110 ms (k_BET=9.1 s^?1).     

Rate coefficients and mechanisms of the reaction of cl‐atoms with a series of unsaturated hydrocarbons under atmospheric conditions

Rate coefficients and/or mechanistic information are provided for the reaction of Cl‐atoms with a number of unsaturated species, including isoprene, methacrolein ( MACR ), methyl vinyl ketone ( MVK ), 1,3‐butadiene, trans‐2‐butene, and 1‐butene. The following Cl‐atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 ± 0.6) × 10^?10cm³ molecule^?1 s^?1 (independent of pressure from 6.2 to 760 Torr); k( MVK ) = (2.2 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k( MACR ) = (2.4 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k(trans‐2‐butene) = (4.0 ± 0.5) × 10^?10 cm³ molecule^?1 s^?1; k(1‐butene) = (3.0 ± 0.4) × 10^?10 cm³ molecule^?1 s^?1. Products observed in the Cl‐atom‐initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH₂O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1‐chloro‐3‐methyl‐3‐buten‐2‐one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO₂ (58 ± 5%), CH₂O (47 ± 7%), CH₃OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK ; CO (52 ± 4%), chloroacetone (42 ± 5%), CO₂ (23 ± 2%), CH₂O (18 ± 2%), and HCOCl (5%) from MACR ; CH₂O (7 ± 1%), HCOCl (3%), acrolein (≈3%), and 4‐chlorocrotonaldehyde (CCA, not quantified) from 1,3‐butadiene; CH₃CHO (22 ± 3%), CO₂ (13 ± 2%), 3‐chloro‐2‐butanone (13 ± 4%), CH₂O (7.6 ± 1.1%), and CH₃OH (1.8 ± 0.6%) from trans‐2‐butene; and chloroacetaldehyde (20 ± 3%), CH₂O (7 ± 1%), CO₂ (4 ± 1%), and HCOCl (4 ± 1%) from 1‐butene. Product yields from both trans‐2‐butene and 1‐butene were found to be O₂‐dependent. In the case of trans‐2‐butene, the observed O₂‐dependence is the result of a competition between unimolecular decomposition of the CH₃CH(Cl)? CH(O?)? CH₃ radical and its reaction with O₂, with k_decomp/k_O2 = (1.6 ± 0.4) × 10¹⁹ molecule cm^?3. The activation energy for decomposition is estimated at 11.5 ± 1.5 kcal mol^?1. The variation of the product yields with O₂ in the case of 1‐butene results from similar competitive reaction pathways for the two β‐chlorobutoxy radicals involved in the oxidation, ClCH₂CH(O?)CH₂CH₃ and ?OCH₂CHClCH₂CH₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334–353, 2003     

Simultaneous Determination of Dopamine and Ascorbic Acid Using the Nano‐Gold Self‐Assembled Glassy Carbon Electrode

Electrochemical behavior of dopamine (DA) was investigated at the gold nanoparticles self‐assembled glassy carbon electrode (GNP/LC/GCE), which was fabricated by self‐assembling gold nanoparticles on the surface of L ‐cysteine (LC) modified glassy carbon electrode (GCE) via successive cyclic voltammetry (CV). A pair of well‐defined redox peaks of DA on the GNP/LC/GCE was obtained at E_pa=0.197 V and E_pc=0.146 V, respectively. And the peak separation between DA and AA is about 0.2 V, which is enough for simultaneous determination of DA and AA. The peak currents of DA and AA were proportional with their concentrations in the range of 6.0×10^?8–8.5×10^?5 mol L^?1 and 1.0×10^?6–2.5×10^?3 mol L^?1, with the detection limit of 2.0×10^?8 mol L^?1 and 3.0×10^?7 mol L^?1 (S/N=3), respectively. The modified electrode exhibits an excellent reproducibility, sensibility and stability for simultaneous determination of DA and AA in human serum with satisfactory result.     

Kinetics of the reactions of OH radicals with 2‐methoxy‐6‐(trifluoromethyl)pyridine,diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol at 298 ± 2 K

Rate constants for the reactions of 2‐methoxy‐6‐(trifluoromethyl)pyridine, diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with OH radicals have been measured at 298 ± 2 K using a relative rate method. The measured rate constants (cm³ molecule^?1 s^?1) are (1.54 ± 0.21) × 10^?12 for 2‐methoxy‐6‐(trifluoromethyl)pyridine, (1.19 ± 0.25) × 10^?10 for diethylamine, and (1.76 ± 0.38) × 10^?12 for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol, where the indicated errors are the estimated overall uncertainties including those in the rate constants for the reference compounds. No reaction of 2‐methoxy‐6‐(trifluoromethyl)pyridine with gaseous nitric acid was observed, and an upper limit to the rate constant for the reaction of 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with O₃ of <7 × 10^{? 20} cm³ molecule^?1 s^?1 was determined. Using a 12‐h average daytime OH radical concentration of 2 × 10⁶ molecule cm^?3, the lifetimes of the volatile organic compounds studied here with respect to reaction with OH radicals are 7.5 days for 2‐methoxy‐6‐(trifluoromethyl)pyridine, 1.2 h for diethylamine, and 6.6 days for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol. Likely reaction mechanisms are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 631–638, 2011     

Electrochemical Behavior and Determination of L‐Tyrosine at Single‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

Based on single‐walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE/SWCNTs), a novel method was presented for the determination of L ‐tyrosine. The GCE/SWCNTs exhibited remarkable catalytic and enhanced effects on the oxidation of L ‐tyrosine. In 0.10 mol/L citric acid‐sodium citrate buffer solution, the oxidation potential of L ‐tyrosine shifted negatively from +1.23 V at bare GCE to +0.76 V at GCE/SWCNTs. Under the optimized experimental conditions, the linear range of the modified electrode to the concentration of L ‐tyrosine was 5.0×10^?6–2.0×10^?5 mol/L (R₁=0.9952) and 2.7×10^?5–2.6×10^?4 mol/L (R₂=0.9998) with a detection limit of 9.3×10^?8 mol/L. The kinetic parameters such as α (charge transfer coefficient) and D (diffusion coefficient) were evaluated to be 0.66, 9.82×10^?5 cm² s^?1, respectively. And the electrochemical mechanism of L ‐tyrosine was also discussed.     

Benzodifuran‐containing well‐defined π‐conjugated polymers for photovoltaic cells

Two well‐defined alternating π‐conjugated polymers containing a soluble electroactive benzo[1,2‐b:4,5‐b′]difuran (BDF) chromophore, poly(BDF‐(9‐phenylcarbazole)) (PBDFC), and poly(BDF‐benzothiadiazole) (PBDFBTD) were synthesized via Sonogashira copolymerizations. Their optical, electrochemical, and field‐effect charge transport properties were characterized and compared with those of the corresponding homopolymer PBDF and random copolymers of the same overall composition. All these polymers cover broad optical absorption ranges from 250 to 750 nm with narrow optical band gaps of 1.78–2.35 eV. Both PBDF and PBDFBTD show ambipolar redox properties with HOMO levels of ?5.38 and ?5.09 eV, respectively. The field‐effect mobility of holes varies from 2.9 × 10^?8 cm² V^?1 s^?1 in PBDF to 1.0 × 10^?5 cm² V^?1 s^?1 in PBDFBTD. Bulk heterojunction solar cell devices were fabricated using the polymers as the electron donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as the electron acceptor, leading to power conversion efficiencies of 0.24–0.57% under air mass 1.5 illumination (100 mW cm^?2). These results indicate that their band gaps, molecular electronic energy levels, charge mobilities, and molecular weights are readily tuned by copolymerizing the BDF core with different π‐conjugated units. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.