Studies on State-to-State Energy Transfer of Electronically Excited Atoms and Molecules

Rotationally inelastic collisions of NH₂( òA₁), ∑(0,9,0), 3₀₃, 1₀₁ have been studied by measuring the dispersed fluorescence spectra at molecular beam conditions. The results show that the angular momentum transfer rule is much more successful than is that predicted by energy gap law for fitting the rotational energy transfer rate. For ΔN < 2 the transfer rates are getting slow down. Downward transfer rates are faster than those of upward transfer. With same angular momentum transferred, the transfer rates for Δk_a = 0 process are larger than those for Δk_a≠0. It is also found that rotation transfer process is a very efficient way for decaying of the initially pumped levels. About 60% of the initially pumped 3₀₃ is colliding into other rotational levels. Energy transfer reactions of metastable rare gas atoms (R_g*) with N₂, NH₃, CS₂ were investigated by measuring the emission spectra. The preferential population of n(A″) of NH(c¹II) was found in He(2³S) + NH₃ reaction, the experimental data shows II(A″)/II(A′) = 1.2 at J′ < 13. A high vibrational excitation and low rotational excitation of N₂(C³n) were observed in Ne(³P₀₂) + N₂ reaction comparing with Ar(³P_0.2) + N₂ reaction. The detailed vibrational populations of CS₂⁺ (Ã, B?) achieved by He(2³S)/Ne(³P_0.2) + CS₂ reaction are different from those obtained by PES. The vibrational distributions of CH(A²Δ) obtained by He(2³S) + CHC1₃ (CH₃NO₂) reactions were discussed based on statistical theory, special attention was paid to reveal the role played by tie angular momentum restriction in this process. The result on energy transfer between N₂(a¹ Π) and CO(X¹ ∑) was firstly presented by VUV emission spectra at single collision condition. The mechanisms of energy transfer related to some of the reactions mentioned above were also discussed in the text.     

Coordinative Chain Transfer Polymerization of Butadiene with Functionalized Aluminum Reagents

Functionalized aluminum alkyls enable effective coordinative chain transfer polymerization with selective chain initiation by the functionalized alkyl. (ω‐Aminoalkyl)diisobutylaluminum reagents (12 examples studied) obtained by hydroalumination of α‐amino‐ω‐enes with diisobutylaluminum hydride promote the stereoselective catalytic chain growth of butadiene on aluminum in the presence of Nd(versatate)₃, Cp*₂Nd(allyl), or Cp*₂Gd(allyl) precatalysts and [PhNMe₂H⁺]/[B(C₆F₅)₄^?]. Carbazolyl‐ and indolylaluminum reagents result in efficient molecular weight control and chain initiation by the aminoalkyl rather than the isobutyl substituent bound to aluminum. As confirmed for (3‐(9H‐carbazol‐9‐yl)propyl)‐initiated polybutadiene (PBD), for example, by deuterium quenching studies, polymer chain transfer by β‐hydride transfer is negligible in comparison to back‐transfer to aluminum.     

Decomposition of alkyl hydroperoxide by a copper(I) complex: insights from density functional theory

The B3LYP theory and scaled hypersphere search method are utilized to explore pathways of (HO)₂PS₂Cu-mediated CH₃OOH decomposition, a model reaction of alkyl hydroperoxide with cuprous dialkyldithiophosphate [(RO)₂PS₂Cu]. It is found that the decomposition of CH₃OOH mediated by the copper(I) complex may lead to formaldehyde and water molecules via O-O bond heterolysis and subsequent intramolecular hydrogen transfer, with retainment of the copper(I) complex. The subsequent hydrogen transfer event and formation of water may add new understanding to the (RO)₂PS₂Cu-mediated decomposition process of alkyl hydroperoxide. The oxygen transfer from CH₃OOH to (HO)₂PS₂Cu moiety, as an O-O bond cleavage manner of CH₃OOH, is also found to occur.     

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp₂ZrCl₂ and rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂ as a catalyst) and styrene (Cp*Ti(OMe)₃ as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp₂ZrCl₂/MAO, whereas it became less effective when the catalyst changed to rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp₂ZrCl₂/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂/MAO. In the case of styrene polymerization with Cp*Ti(OMe)₃/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010     

Photoinduced electron transfer in some photosensitive molecules-incorporated semiconductor/zeolites: New photocatalytic systems

An intramolecular charge transfer (ICT) molecule,p-N,N-dimethyl-aminobenzoic acid (DMABA) has been studied in zeolite and colloidal media. The ratio of ICT to normal emission (ICT/LE) is greatly enhanced in zeolites compared to that in polar solvents. The ICT emission of DMABA was quenched by increasing the concentration of TiO₂ colloids, while the normal emission was slightly enhanced. Upon illumination of the heteropoly acid (HPA) incorporated TiO₂ colloids, interfacial electron transfer takes place from the conduction band of TiO₂ to the incorporated HPA which is also excited to catalyze the photoreduction of Methyl Orange. It is found that the interfacial electron transfer mechanism of HPA/TiO₂ is quite analogous to the Z-scheme mechanism for plant photosynthetic systems. In DMABA-adsorbed TiO₂/Y-zeolite the ICT/LE ratio of DMABA is quite small implying that electron transfer takes place from DMABA to the conduction band of TiO₂. This results in drastic enhancement in the photocatalytic activity of DMABA-adsorbed TiO₂/Y-zeolite compared to free TiO₂/Y-zeolite.     

Mechanism of the carbonylation of dicyclopentadienylmolybdenum dihydride

The carbonylation of Cp₂MoH₂ proceeds through the intermediates Cp₂MoCO, [Cp₂Mo(H)CO] [CpMo(CO)₃] (I) and CpMo(CO)₃ to the final products [CpMo(CO)₃]₂ and CpMo(η³-C₅H₇)(CO)₂. The formation of I in the carbonylation reaction has been shown to involve net hydride transfer, but an alternate synthesis has demonstrated the considerable proton basicity of Cp₂MoCO. Since the net hydride transfer between Cp₂MoH₂ and [CpMo(CO)₃]₂ can be accelerated by production of metal centered radicals, the actual mechanism is not a simple two-electron process (H^? transfer, but rather a sequence of one-electron steps.     

掺杂双(N-2-甲基苯基-水杨醛亚胺)合铜(II)配合物的碳糊电极电催化测量过氧化氢HosseinKhoshro,HamidR.Zare,RasoulVafazadeh简

The electrochemical behavior of a bis(N-2-methylphenyl-salicyldenaminato)copper(Ⅱ) complex spiked in a carbon paste electrode (BMPSCu-CPE) and its electrocatalytic reduction of H₂O₂ were examined using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry. Cyclic voltammetry was used to study the redox properties of BMPSCu-CPE at various potential scan rates. The apparent charge transfer rate constant and the transfer coefficient for the electron transfer between BMPSCu and the carbon paste electrode (CPE) were 1.9±0.1 s^-1 and 0.43, respectively. BMPSCu-CPE had excellent electrocatalytic activity for H₂O₂ reduction in 0.1 mol/L phosphate buffer solution (pH 5.0), and it decreased the overpotential by 300 mV as compared to CPE alone. The diffusion coefficient and kinetic parameters such as the heterogeneous catalytic electron transfer rate constant and electron transfer coefficient for the reduction of H₂O₂ at the BMPSCu-CPE surface were also determined using electrochemical methods. Differential pulse voltammetry showed two linear dynamic ranges of 1.0-10.0 and 10.0-300.0 μmol/L and a detection limit of 0.63 μmol/L H₂O₂. The BMPSCu-CPE has excellent reproducibility and long term stability, and it was successfully applied for the determination of H₂O₂ in two pharmaceutical samples: an antiseptic solution and a hair dying cream.     

Mechanism of B-H Redistribution during Reduction of Polyborazylene by Hydrazine

Density functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia-borane (H₃B−NH₃, AB ) from polyborazylene (B_xN_xH_x, PBz ) in the presence of hydrazine (H₂N−NH₂, Hz ). Herein, borazine (B₃N₃H₆, Bz ) is used as the simplest relevant model of PBz for the regeneration process. Digestion of Bz using Hz was found to occur by a string of Lewis acid base adduct (between B atoms of Bz and Hz molecule) formation and Hz assisted proton transfer processes. Later, B−H bonds of HB(NHNH₂)₂, the Bz digested product, are redistributed to form hydrazine-borane (H₃B−NH₂NH₂, HzB ) and B(NHNH₂)₃. Redistribution of B−H bonds occurs through hydroboration and concerted proton-hydride transfer. Another B−H redistributed product, B(NHNH₂)₃, produces HzB as a result of proton and hydride transfer from cis-diazene ( Dz ), the oxidized product of Hz in presence of O₂.     

Acceleration of the single electron transfer–degenerative chain transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride in water at 25 °C

The accelerated single electron transfer–degenerative chain transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride (VC) in H₂O/tetrahydrofuran (THF) at 25 °C is reported. This process is catalyzed by sodium dithionite (Na₂S₂O₄)‐sodium bicarbonate (NaHCO₃). Electron transfer cocatalysts (ETC) 1,1′‐dialkyl‐4,4′‐bipyridinum dihalides or alkyl viologens were also employed in this polymerization. The resulting poly(vinyl chloride) (PVC) has a number‐average molecular weight (M_n) = 2,000–12,000, no detectable amounts of structural defects, and both active chloroiodomethyl and inactive chloromethyl chain ends. The molecular weight distribution of PVC obtained is M_w/M_n = 1.5. The surface active agents afford the final polymers as a powder and provide an acceleration of the rate of polymerization. The role of ETC is to accelerate the single electron transfer (SET) step, whereas THF enhances the degenerative chain transfer (DT) step. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6364–6374, 2004     

Photoinduced Energy and Electron Transfer in Phenylethynyl‐Bridged Zinc Porphyrin–Oligothienylenevinylene–C60 Ensembles

Donor–bridge–acceptor triad (Por‐2TV‐C₆₀) and tetrad molecules ((Por)₂‐2TV‐C₆₀), which incorporated C₆₀ and one or two porphyrin molecules that were covalently linked through a phenylethynyl‐oligothienylenevinylene bridge, were synthesized. Their photodynamics were investigated by fluorescence measurements, and by femto‐ and nanosecond laser flash photolysis. First, photoinduced energy transfer from the porphyrin to the C₆₀ moiety occurred rather than electron transfer, followed by electron transfer from the oligothienylenevinylene to the singlet excited state of the C₆₀ moiety to produce the radical cation of oligothienylenevinylene and the radical anion of C₆₀. Then, back‐electron transfer occurred to afford the triplet excited state of the oligothienylenevinylene moiety rather than the ground state. Thus, the porphyrin units in (Por)‐2TV‐C₆₀ and (Por)₂‐2TV‐C₆₀ acted as efficient photosensitizers for the charge separation between oligothienylenevinylene and C₆₀.     

NHC→SiCl4: An Ambivalent Carbene‐Transfer Reagent

The addition of BCl₃ to the carbene‐transfer reagent NHC→SiCl₄ (NHC=1,3‐dimethylimidazolidin‐2‐ylidene) gave the tetra‐ and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl₃]⁺ and [(NHC)₂SiCl₃]⁺ with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC→SiCl₄ served as a transfer reagent for the NHC ligand. The addition of BF₃ ? OEt₂, on the other hand, gave NHC→BF₃ as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C₂F₅)₂SiCl₂ was treated with NHC→SiCl₄. In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl₃]⁺ and [(NHC)₂SiCl₃]⁺ were detected with [(C₂F₅)SiCl₃]^? as counterion. A similar result was already reported for the reaction of NHC→SiCl₄ with (C₂F₅)₂SiH₂, which gave [(NHC)₂SiCl₂H][(C₂F₅)SiCl₃]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC→Si(C₂F₅)₂Cl₂ and NHC→Si(C₂F₅)₂ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron‐poor silylenes. Furthermore, the reactivity of NHC→SiCl₄ towards phosphines is discussed. The carbene complex NHC→PCl₃ shows similar reactivity to NHC→SiCl₄, and may even serve as a carbene‐transfer reagent as well.     

Solvent Effect on the Kinetics of Oxidation of [Co(en)2SCH2CH2 NH2]2+ by S2O8 2−

The effect of the solvent on rate of the oxidation of [Co(en)₂SCH₂CH₂NH₂]²⁺ by S₂O₈ ²⁻ in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (Bu ^t OH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔG _t°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light

Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl₄^?_(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O₂ through the transfer of SPR‐excited hot electrons to O₂ molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O₂ molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O₂ charge‐transfer process.     

β‐Diketiminate‐supported magnesium alkyl: synthesis,structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η²‐HC[C(Me)NMes]₂} ( 2 ) (Mes = mesityl, 2,4,6‐Me₃C₆H₂), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH₄)₂(THF)₂ ( 1 ) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1 , 2 and Al(i‐Bu)₃ leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.     

Catalytic electrooxidation of hydrazine at the nickel ferricyanide modified electrode: can an array of surface bound one-electron redox centers act in concert?

The [NiFe(CN)₆]^2−/− derivatized nickel electrode represents an electrocatalytic surface for the mediated oxidation of hydrazine. The four-electron oxidation of hydrazine is employed as a probe of multiple electron charge transfer processes at the Ni[Fe(CN)₆]^2−/− interface since the observed product distribution is sensitive to the detailed mechanism and stoichiometry of electron transfer giving rise to production of NH₃ if only one-electron transfer processes occur, while yielding N₂H₂ or N₂ if multi-electron processes are present. A correlation between surface overlayer structure and charge transfer pathway is observed. A rather facile, pseudo-first order heterogeneous charge transfer rate (~3 × 10⁻² cm s⁻¹) was found for N₂ production. The kinetics of the processes involved in this electrocatalysis were analyzed according to the Savéant-Andrieux theory. The electrocatalytic behavior of this system can be varied from R type behavior to R + S or (SR) and then to S + E behavior by varying the amount of the surface attached catalyst.     

Single‐Site Copper(II) Water Oxidation Electrocatalysis: Rate Enhancements with HPO42− as a Proton Acceptor at pH 8

The complex Cu^II(Py₃P) ( 1 ) is an electrocatalyst for water oxidation to dioxygen in H₂PO₄^?/HPO₄^2? buffered aqueous solutions. Controlled potential electrolysis experiments with 1 at pH 8.0 at an applied potential of 1.40 V versus the normal hydrogen electrode resulted in the formation of dioxygen (84 % Faradaic yield) through multiple catalyst turnovers with minimal catalyst deactivation. The results of an electrochemical kinetics study point to a single‐site mechanism for water oxidation catalysis with involvement of phosphate buffer anions either through atom–proton transfer in a rate‐limiting O? O bond‐forming step with HPO₄^2? as the acceptor base or by concerted electron–proton transfer with electron transfer to the electrode and proton transfer to the HPO₄^2? base.     

Magnesium(II) Complexes with High Emission: The Distinct Charge‐Transfer Process from Transition Metal

Generally, the first‐row transition‐metal complexes are notorious in luminescence materials because of their metal‐ligand charge transfer in emission process. Herein, we rationally used magnesium instead the first‐row transition metal to coordinate with 2‐(anthracen‐9‐yl)‐1H‐imidazo[4,5‐f][1,10]phenanthroline (AIP) in the construction of luminescent complexes. Further investigation revealed AIP could work as detector for quantitative determination of Mg²⁺ cation. Comparing to other divalent cations, this fluorescence sensor exhibited high selectivity for the quantitative determination of Mg²⁺ with the low limit of detection (5 × 10^–7 m ). Through X‐ray single crystal diffraction, the crystal structures of [Mg(AIP₂)(NO₃)₂ · (H₂O)₄] ( 1 ), [Mn(AIP)(NO₃) · EtOH] ( 2 ), and [Co₂(AIP)₂Cl₄ · (MeOH)₂] ( 3 ) were observed in various arrangements. The theory calculations based on crystal structures indicated the Mg^II complex undergoes distinct charge‐transfer process from other transition‐metals based compounds, in which charge‐transfer excited‐state lifetimes were deactivated rapidly through metal‐to‐ligand charge‐transfer (MLCT) process. This study provided insight into construction of luminescence compounds by using d⁰ metals in main groups instead of transition metals.     

Reactions of NO2+ and solvated NO2+ ions with aromatic compounds and alkanes

The rate constants and modes of reaction of NO₂⁺ and C₂H₅ONO₂NO₂⁺ with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and substitution reactions (NO₂⁺ + M → MO⁺ + NO; C₂H₅ONO₂NO₂⁺ + M → MNO₂⁺ + C₂H₅ONO₂) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C₂H₅ONO₂NO₂⁺ ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO₂⁺ and C₂H₅ONO₂. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C₂H₅ONO₂NO₂⁺ ions, on the energetics of the competing charge transfer process. Both NO₂⁺ and C₂H₅ONO₂NO₂⁺ undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k (collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO₂⁺.     

Redox kinetics of metal complexes in nonaqueous solutions. V. Kinetics and mechanism of the iron (II) reduction of the acetylacetonates of manganese (III) and cobalt (III) in acetonitrile

The electron transfer step of the reduction of Mn(acac)₃ and Co(acac)₃ by Fe(II) in acetonitrile is preceded by the one-ended dissociation of an acac ligand and the formation of a binuclear bridged complex. After the electron transfer has taken place through the bridging ligand, the complex dissociates into the products M(acac)₂ (M = Mn, Co) and Fe(acac)²⁺. These primary reaction products could not be identified, since the transfer of acac from M(acac)₂ to Fe(acac)²⁺ is too rapid, producing ultimately Fe(acac)₃ and M²⁺. The M(III)-oxygen cleavage is accelerated by M(acac)₂. Furthermore, the dissociation of the binuclear intermediate is catalyzed by the M(acac)₃ reactant. Mn(acac)₃ is reduced more than a thousand times faster than Co(acac)₃.     

香豆素343敏化TiO2纳米粒子光致电子转移的荧光和拉曼光谱

通过对香豆素343(C343)染料敏化TiO₂纳米粒子光致电子转移的荧光和拉曼光谱特性的研究表明,C343染料敏化TiO₂纳米粒子稳态吸收光谱和稳态荧光光谱的红移归因于从被吸附的C343染料分子激发态和C343/TiO₂复合物到TiO₂纳米粒子导带的光致电子转移. 由时间分辨荧光光谱确定了C343染料敏化TiO₂纳米粒子的逆向电子转移速率常数为τ₁=31 ps. C343 染料敏化TiO₂纳米粒子体系拉曼光谱的研究表明, 被吸附在界面处的染料分子主链碳键的伸缩振动和碳环的呼吸运动的振动模式对超快界面光致电子转移有着重要的促进作用.