苯硝化反应中电子转移反应重组能的计算

提出了重组能的量子化学算法,在用CISD/6-31G基组水平上,得到苯硝化反应中反应物及过渡态的结构.并计算了各自交换电子转移反应以及交叉电子转移反应的重组能,同实验重组能进行了比较.计算用了Gaussian 94程序.从重组能的角度分析了苯硝化反应.结果表明,对于NO2++NO2→NO2+NO2+的自交换电子转移反应,重组能较大,结论为: 在芳烃硝化反应中,存在以NO2+为氧化剂的电子转移步骤的可能性很小,而从动力学的角度上,用NO+作反应的氧化剂更有可能.     

Inorganic Photochemistry:Past,Present, and Future

Transition metal complex, in its electronic excited state, has intriguing photophysical and photochemical properties that are substantially different from its ground state, Indeed, electronically excited metal complex can be viewed as hot chemical species that is readily synthesized by photo-excitation with UV-visible light. If the energy of excited metal complex can be properly manipulated, it may be possible to devise new catalytic system for converting light to chemical energy. In the context of energy conversion reactions and chemical sensing, it is important for biomolecular reactions at room temperature. Among the photochemical bimolecular reactions, the following three have the widest applications in photocatalysis, and these are (1) bimolecular outer-sphere electron transfer reactions, (2) bimoleculat inner-sphere atom transfer/abstract reactions, and (3) exciplex formation involving electronic excited state. The past of inorganic photochemistry has demonstrated the success of[Ru(bpy)₃]²⁺ as a powerful reagent for light-induced electron transfer reactions. Much of the current photochemistry research focus on coordinative unsaturated metal complexes, that are strongly photoluminescent and readily undergo substrate binding reactions in their excited states. In this lecture, I will review some of the past successful stories of[Ru(bpy)₃]²⁺ and discuss our current research on the luminescent metal-complexes prepared in my laboratory. I will end my lecture by proposing a clue for achieving light-induced multi-electron transfer reactions, which remains a challenge in photochemistry research.     

Correlation study of Franck-Condon barriers associated with electron self-exchange reactions with ionization potentials and electron affinities and experimental Born-Oppenheimer potentials

An accurate theoretical scheme for obtaining directly the Franck-Condon barrier associated with the electron self-exchange reaction from ionization potentials and electron affinities is presented. Applicability is tested using some diatomic molecular redox couples. The corresponding ionization potentials and electron affinities are obtained from the Born-Oppenheimer potential energy curves which are directly determined from the experimental vibration-rotational spectroscopic data. The Franck-Condon barriers are calculated for the electron self-exchange reactions and are also compared with those from other theoretical methods.     

Ab initio molecular orbital calculations on some selected boron(I) hydrides

Ab initio LCAO-MO-SCF Hartree-Fock-Roothaan calculations have been carried out for a series of closed-shell boron hydrides (B³⁺, B⁺ BH, BH₂⁻,BH₂⁺, BH₃ and BH₄⁻). Koopmans' theorem vertical ionization potentials for the core and highest occupied molecular orbitals are presented. Proton and hydride affinities of some of these molecules have been calculated along with the energies of reaction between various pairs of these boron hydrides.     

Cationic and anionic states of CF, CCl, SiF and SiCl. Some new information derived using translational energy spectroscopy

Translational-energy spectroscopy was applied to collisional-excitation and charge-inversion reactions of CF⁺, CCl⁺, SiF⁺ and SiCl⁺ in order to gain energetic and bond-length information about the anionic and excited-cationic states of the title molecules. The excitation spectra revealed that the ã³Π state, known in CCl⁺ and SiCl⁺, has a term energy of 4.85 ± 0.15 eV in CF⁺ and 4.70 ± 0.20 eV in SiF⁺, while the 1¹Π state, known in CCl⁺, is not below the dissociation threshold in CF⁺, SiF⁺ and SiCl⁺. These data, and bond-length estimates for the ã³Π states, are consistent with documented ab initio predictions except for r_e of CF⁺(ã³Π) which seems to be larger than 1.21 Å. Charge-inversion spectra indicated that beams of monohalide cations formed from the tetrahalides, contained substantial proportions of ã³Π-state ions, and, in the case of CCl, SiF and SiCl, the broadness of spectral peaks was taken as evidence for the stability of the ã¹Δ-state anion. Adiabatic electron affinities were deduced to be 0.49 ± 0.15 eV, 0.89 ± 0.20 eV, 1.34 ± 0.30 eV and 1.40 ± 0.30 eV for the title molecules, respectively.     

Protonation of group 14 oxides: the proton affinity of SnO

Molecular orbital calculations are reported for the monoxides, XO, of group 14 elements (X = C, Si, Ge and Sn) and for both isomers, XOH⁺ and HXO⁺, of the protonated monoxides. Structure optimisation has been carried out using the Density Functional Theory employing the B3LYP procedure and at both Hartree-Fock and MP2 (full) levels, all with a variety of medium-sized Gaussian basis sets. In all XO molecules the oxygen atom is the preferred site for protonation, except when X = C where HCO⁺ is the lower energy isomer. Barriers to interconversion between the two isomers XOH⁺ and HXO⁺ are over-estimated by the Hartree-Fock calculations, but with wave functions that include electron correlations they generally fall into the range 27-44 kcal mol⁻¹. Proton affinities increase as the atomic number of X increases, and values calculated by averaging over all wave functions that include electron correlation, give the following proton affinities: for CO, 141.5; for SiO, 189.3; for GeO, 196.1; and for SnO, 215.6 (all in kcal mol⁻¹).     

Potential energy curves: A simple and rapid method

The true potential energy curves for different electronic states of diatomic molecules have been constructed by a simplified and modified form of the Jarmain method. To check the validity of this new procedure potential energy curves are constructed for NO⁺, VO, Si₂, AsO, AsO⁺, PF⁺, CO and Bi₂. The results are in good agreement with the Jarmain, RKRV and Lakshman and Rao methods.     

Synthesis of (thia)Calixarene-based exTTF Derivatives and Their Electron Transfers Towards p-Chloranil and C60

Two novel (thia)calixarene-based exTTF derivatives(3a and 3b) were prepared by Mitsunobu reactions in toluene using diethyl azodicarboxylate(DEAD) and triphenylphosphine(PPh₃) system. The cyclic voltammograms of compounds 3a and 3b were provided, and two electron-irreversible waves with redox potentials were observed. Meanwhile, the intermolecular electron transfer(ET) properties of both compounds 3a and 3b towards p-chloranil(Q) and C₆₀ were investigated via UV-Vis and fluorescent spectroscopies, respectively. The results indicated that the introduced nonoxidable metal ions(Al³⁺, Pb²⁺, Sc³⁺) might promote the intermolecular ET from compounds 3a and 3b towards Q ensembles, whereas the effects of Sc³⁺ were the most impressive. Furthermore, the effects of the same metal ions(Al³⁺, Pb²⁺, Sc³⁺) added for compound 3b were greater than those for compound 3a. Additionally, the photoinduced intermolecular ET from compounds 3a and 3b towards C₆₀ was observed.     

Scaling for Experimental Inner-Sphere Reorganization Energy of Hydrated Ions via Accurate Potential Function

Reported here are several new calculation methods for the inner-sphere reorganization energy of hydrated metal ions involved in electron transfer processes.It is based on the self-exchange model of reorganization and utilizes the more exact potential functions between central metal ion and the inner-sphere ligands.The parameters involved are determined via the spectroscopic and thermodynamic data.The predictions of the inner-sphere reorganization energies from those models agree well with the photoemission experimental results.     

Reversibility of electrode reactions involving organic compounds

A general empirical approach allowing one to describe the kinetics and evaluate the mechanism of the electrode electron transfer reactions is offered. The approach is based on the electrode potentials, the vertical ionization potentials (oxidation), and the affinity to electron (reduction). An equation linking kinetic and thermodynamic parameters is derived. Electrode reactions involving organic compounds are discussed in polarographic terms. The conclusion is drawn that most electron transfer reactions involving organic compounds are reversible, and that the irreversibility of the net electrode reaction is due to the irreversibility of subsequent chemical and electrochemical stages. An experimental observation of the slow electron transfer is possible in the cases of a substantial reorganization of molecules in the presence of fast subsequent chemical and electrochemical reactions.     

The donor-acceptor properties of exciplexes. Comparison of fluorescence quenching of excited aromatic molecules and their exciplexes

Exciplex reactivity in electron transfer reactions is investigated. Methods are proposed for the calculation of exciplex ionization potentials and electron affinities. Exciplex quenching rate constants have been measured. It is shown that exciplex quenching follows the same laws as that of excitcd molecules. Conditions of specific exciplex quenching are considered.     

Nonempirical ab initio studies on inner-sphere reorganization energies of M2+(H2O)6/M3+(H2O)6 redox couples at valence basis level

On the basis of the basic feature of the electron transfer reactions, a new theoretical scheme and application of a nonempirical ab initio method in computing the inner-sphere reorganization energies (RE) of hydrated ions in electron transfer processes in solution are presented at valence STO basis (VSTO) level. The potential energy surfaces and the various molecular structural parameters for transition metal complexes are obtained using nonempirical molecular orbital (MO) calculations, and the results agree very well with experimentally observed ones from vibrational spectroscopic data. The results of inner-sphere REs obtained from these calculations via this new scheme give a good agreement with photoemission experimental findings and those from the improved self-exchange model proposed early for M²⁺(H₂O)₆/M³⁺(H₂O)₆(M = V, Cr, Mn, Fe, and Co) redox couple systems and are better than those from semiempirical INDO/II MO method and other classical methods. Further, the observed agreement of the optimized structural data and the results of inner-sphere REs of complexes with experimental findings confirms the following: (1) the validity of nonempirical MO calculation method to get accurate structural parameters and inner-sphere RE for the redox systems for which reliable vibrational spectroscopic data are not available, (2) the validity of the improved self-exchange model proposed early for inner-sphere RE, and (3) the reasonableness of some approximations adopted in this study. © 1997 John Wiley & Sons, Inc.     

Concerning the Lewis acidity of NO and NO2 as measured by their affinity to selected bases

Recently published theoretical results concerning the NO⁺ and NO₂⁺ gas-phase affinities of a few selected molecules, as well as the correlation between the above quantities and the corresponding proton affinities, are examined in the context of the much larger body of experimental and theoretical data already reported in the literature.     

REACTIVITY OF ACRIDINE DYE TRIPLET STATES IN ELECTRON TRANSFER REACTIONS

Abstract—Rate constants, k _q , for the reaction of cationic and neutral acridine orange and 10-methylacridine orange triplet states (³AOH ⁺, ³AO, ³MAO⁺) with a series of electron donors have been measured. Two different protolytic forms of the semireduced dye radical are produced by acridine orange triplet quenching at various pH^M values in methanolic solution.
It is found that k ₄ decreases with increasing oxidation potential of the reducing agent for all triplet states in a manner which is expected for electron transfer reactions. The different reactivities of the cationic and neutral triplet forms can, therefore, be attributed to the difference in reduction potentials of these species. The difference in reduction potentials is related to the p K ^M values of triplet state, p K _T^M , and semireduced dye radical, p K ^M_S , by thermodynamic consideration. p K _T^M (³AOH⁺/³AO) is determined to be 11.2. From thisp K _S^M (AOH./AO;) is estimated to be 17–18. This is in striking contrast to the protolytic equilibrium of the semireduced dye radicals found to be pK^F= 4.1. We conclude that the last value represents the second protonation equilibrium (AOH⁺₂./AOH). This conclusion is confirmed by spectroscopic data.     

Direct calculation of electron transfer parameters through constrained density functional theory

It is shown that constrained density functional theory (DFT) can be used to access diabatic potential energy surfaces in the Marcus theory of electron transfer, thus providing a means to directly calculate the driving force and the inner-sphere reorganization energy. We present in this report an analytic expression for the forces in constrained DFT and their implementation in geometry optimization, a prerequisite for the calculation of electron transfer parameters. The method is then applied to study the symmetric mixed-valence complex tetrathiafulvalene-diquinone radical anion, which is observed experimentally to be a Robin-Day class II compound but found by DFT to be in class III. Constrained DFT avoids this pitfall of over-delocalization and provides a way to find the charge-localized structure. In another application, driving forces and inner-sphere reorganization energies are calculated for the charge recombination (CR) reactions in formanilide-anthraquinone (FA-AQ) and ferrocene-formanilide-anthraquinone (Fc-FA-AQ). While the two compounds have similar reorganization energies, the driving force in FA-AQ is 1 eV larger than in Fc-FA-AQ, in agreement with experimental observations and supporting the experimental conclusion that the anomalously long-lived FA-AQ charge-separated state arises because the electron transfer is in the Marcus inverted region.     

Fast Redox Perturbation of Aqueous Solution by Photoexcitation of Pyranine

Abstract— Intense illumination (60-120 MW/cm²) of an oxygen-free aqueous solution of pyranine (8-hydroxypyrene-l,3,6-tri-sulfonate) by the third harmonic frequency of an Nd-Yag laser (355 nm) drives a two successive-photon oxidative process of the dye. The first photon excites the dye to its first electronic singlet state. The second photon interacts with the excited molecule, ejects an electron to the solution and deactivates the molecule to a ground state of the oxidized dye (φ⁺). The oxidized product, φ⁺, is an intensely colored compound (Λ_max= 445 nm, ε= 43 000 ± 1000 M ⁻¹ cm⁻¹) that reacts with a variety of electron donors like quinols, ascorbate and ferrous compounds. In the absence of added reductant, φ⁺ is stable, having a lifetime of -10 min. In acidic solutions the solvated electrons generated by the photochemical reaction react preferentially with H⁺. In alkaline solution the favored electron acceptor is the ground-state pyranine anion and a radical, φ, of the reduced dye is formed. The reduced product is well distinguished from the oxidized one, having its maximal absorption at 510 nm with e = 25 000 ± 2000 M^-l cm⁻¹. The oxidized radical can be reduced either by φ^- or by other electron donors. The apparent second-order rate constants of these reactions, which vary from 10⁶ up to 10⁹M⁻¹ s⁻¹, are slower than the rates of diffusion-controlled reactions. Thus the redox reactions are limited by an energy barrier for electron transfer within the encounter complex between the reactants.     

萤火虫氧化荧光素及其衍生物的电子结构和光物理性质

通过密度泛函理论(DFT)的MPW3PBE泛函, 对萤火虫生物发光底物氧化荧光素及其衍生物进行了结构全优化. 计算了其电离能、 电子亲和势、 空穴抽取能、 电子抽取能、 空穴和电子重组能, 并评估了其空穴和电子传输能力. 采用含时密度泛函理论(TD-DFT)//MPW3PBE/6-31+G(d)方法计算了吸收光谱, 优化了最低单重态S₁, 研究了其荧光光谱, 进而考察了具有较高发光效率的氧化荧光素作为有机发光二极管(OLED)材料的可能性. 计算结果表明, 氧化荧光素及其衍生物可以同时作为电子传输层和发光层材料.     

Theoretical analysis of electron-transfer crossover reactions between complex ions. Communication 4. Reactions involving ethylenediamine complexes of cobalt and ruthenium

Conclusions Calculations have been made within the bounds of the quantum-mechanical theory of chemical reactions of the rate constants and activation enthalpies of a number of electron transfer reactions involving the ethylenediamine complexes of cobalt and ruthenium. An estimate has been obtained of the inner-sphere reorganization energy for the Co(en)₃ ^3+/2+ complexes. The transmission coefficients for electron transfer in redox systems incorporating ethylenediamine complexes of cobalt and ruthenium have been compared, which enables a conclusion to be drawn on the degree of transferred-electron delocalization in the complexes being compared.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 353–358, February, 1984.     

The inner-sphere reorganization energies for AH2 + AH (A = Al,Si, P,S) electron self-exchange reactions in electron-transfer processes from ab initio calculations

This article presents an application of the accurate calculation scheme proposed recently for the inner-sphere reorganization energies of molecules of the type AH₂ (A = Al, Si, P, and S). A reasonable extension has been made. The inner-sphere reorganization energies for the title thermal electron self-exchange reactions are calculated in terms of ab initio MO self-consistent field method (HFSCF ) at different basis-set levels (6-31G **, 6-31 + G **, DZ , and DZP ) and the involved parameters are also determined. These calculated results have been calibrated by comparing optimized molecular geometrical parameters and corresponding energy properties with the experimental findings or other theoretical values. An approximation, in which the contribution from the bond length–bond angle to the potential energy surface is neglected, is adopted in constructing the calculation formulas via the function model. Its adequacy is discussed. Agreement among different calculation schemes is analyzed. © 1995 John Wiley & Sons, Inc.     

Thermodynamics of silver—silver halide electrodes and thermodynamic solubility products of silver halides in glycerol + water mixtures at different temperatures

The standard potentials of silver—silver bromide and silver—silver iodide electrodes in glycerol+water mixtures containing 5, 10, 20 and 30 wt% glycerol were determined from electromotive force measurements of the cell Ag(s), AgX(s), KX(c)//KCl(c), AgCl(s), Ag(s), where X is Br or I, at seven different temperatures in the range 5–35°C. The standard potentials in each solvent are represented as a function of temperature. The standard thermodynamic functions for the electrode reactions, the primary medium effects of various solvents upon X⁻, and the standard thermodynamic quantities for the transfer of 1 g-ion of X⁻ from water to the respective glycerol + water media are evaluated and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents. From the values of the Ag/Ag⁺ and Ag/AgX, X⁻ electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide and silver iodide have been determined in glycerol + water solvent mixtures at different temperatures.