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1.
The dependence of the formation enthalpy ()H
Ex* and the Gibbs energy (G
Ex*) of exciplexes with partial charge transfer on the Gibbs energy of electron transfer G
et*, the parameters of the electronic structure of an exciplex (the difference in the energies of the charge transfer (CT) state and a locally excited state (LE) in a vacuum ( H
22
0– H
11
0), the matrix element of the electronic coupling of the CT and LE states H
12, the dipole moment of the CT state, and the repulsion energy in an exciplex a"), and the polarity of the medium was analyzed. The consideration of the repulsion energy in the exciplex is necessary for correlation of the experimental values of H
Ex* and the spectral shift of the exciplex emission with respect to the LE state. All of these parameters depend on the particular nature of the exciplex, which is the reason for the lack of the general dependence of H
Ex* and G
Ex* on G
et* for exciplexes with partial charge transfer. 相似文献
2.
Exciplexes of 9-cyanophenanthrene with a series of weak electron donors with the Gibbs energy of electron transfer G
et
* varying in the range –(0.02–0.09) eV were studied. The exciplexes exhibited fairly intense emission both in nonpolar and aprotic polar solvents. The kinetics of the exciplex formation was found to be controlled mainly by diffusion and reactant orientation. This is clearly manifested in the low-temperature region in which the activation enthalpy of exciplex formation is very close to the activation enthalpy of diffusion, and the activation entropy of exciplex formation does not exceed 18 J mol–1 K–1 in absolute value. 相似文献
3.
Activation parameters were studied for the decay of 9-cyanophenanthrene exciplexes with some weak electron donors (the Gibbs energy of electron transfer G
*
et ranging from –0.02 to –0.09 eV), which displayed fairly high emission in both nonpolar and polar aprotic solvents. It was shown that the activation enthalpy of decay for the exciplexes is low, while the activation entropy reaches –(100–150) J mol–1 K–1, which is consistent with the two possible decay mechanisms: by dissociation into free radical ions or by intersystem crossing into the triplet state. 相似文献
4.
Sten Ahrland 《Helvetica chimica acta》1967,50(1):306-318
The different types of bonding in complexes formed in aqueous solution are clearly reflected in the values of ΔH0 and ΔS0 for the complex formation reaction. 相似文献
5.
Canotilho J. Costa F. S. Sousa A. T. Redinha J. S. Leitão M. L. P. 《Journal of Thermal Analysis and Calorimetry》1999,57(1):87-93
Enthalpies of solution of various terfenadine samples in methanol and in ethanol were measured. Samples were prepared by crystallization in different solvents. The calorimetric results give important information on crystal structure of the terfenadine forms and on the solute/solvent interactions of this compound with the solvents.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
6.
The solubilities of donepezil hydrochloride polymorphic form III in methanol, ethanol, 1-propanol and dimethyl formamide were measured at temperatures ranging from 278.15 to 333.15 K at atmosphere pressure using a gravimetrical method. The modified Apelblat model fitted the experimental data well with the root-mean-square deviations less than 6.287 × 10?4. The dissolution enthalpy and entropy of solute were predicted from the solubility data in different solvents using the van’t Hoff equation. The relationships among solubility, temperature, the intermolecular force and hydrogen bonding between solute and solvent, and the viscosity of solvents were investigated. The viscosity and surface tension of solvents affect the dissolution enthalpy and entropy of donepezil hydrochloride polymorphic form III. 相似文献
7.
D. N. Dogadkin E. V. Dolotova I. V. Soboleva M. G. Kuzmin V. F. Plyusnin I. P. Pozdnyakov V. P. Grivin E. Vauthey P. Brodard O. Nicolet 《High Energy Chemistry》2004,38(6):392-400
The dynamics of exciplex and radical ion formation was studied in donor–acceptor systems with G
*
et > –0.1 eV. It was shown that the quenching of excited singlet states of aromatic molecules by electron donors in polar solvents led to the formation of radical ions via exciplex dissociation resulting to complete charge separation. Intersystem crossing and internal conversion into the ground state (back electron transfer) compete with this process. The quantum yields and the rate constants of the radical ion formation were measured. 相似文献
8.
通过多种热化学方法研究了三聚氰胺的热力学性质. 首先用氧弹式燃烧热量计测定了三聚氰胺在298.15 K 时的燃烧热, 根据燃烧热结果, 计算出三聚氰胺的标准摩尔燃烧焓和标准摩尔生成焓, 分别为: △cHΘm=(-2455.17±4.65) kJ·mol-1; △fHΘm =(-763.38±5.16) kJ·mol-1. 然后根据键焓与燃烧焓之间的关系, 估算出三聚氰胺中的C≈N(此键介于单键与双键之间)键能为458.30 kJ·mol-1, 此值介于碳氮单键键能和双键键能之间. 通过绝热热量计测定了三聚氰胺从80到385 K的低温热容. 根据热容值, 计算了此温度区间的标准摩尔生成焓, 其与温度呈线性关系. 另外, 三聚氰胺的热稳定性也用热重-差示扫描量热(TG-DSC)法进行了分析, 确定其分解的DSC曲线的峰顶温度为603.37 K. 相似文献
9.
The role of enthalpy, entropy contributions to the shift of complex formation equilibria inwater-organic solvents was studied. The formation of both ammonia and carboxylate complexes of d-metalions was found to be presumably enthalpy-controlled. The role of entropy changes increases in binary solvents with a high level of supramolecular organization, and also in the case of formation of complexes of the highest orders, when the coordination of ligands is accompanied either by a complete displacement of solvent molecules from the inner coordination sphere or by a change in the complex structure. Thus found regularities can be applied for the prediction of heat effects of complex formation in water-organic solvents. In the fist communication [1] of this series we have considered the effects of the nature and composition of water-organic solvents on the stability of ammonia and carboxylate complexes of d-metal ions. This work is based on the data of our recent thermochemical works [2-22] and is dedicated to the study of the role of enthalpy and entropy contributions to the shift of the complex formation equilibria in water-organic solvents. 相似文献
10.
Environment‐Sensitive Behavior of DCNP in Solvents with Different Viscosity,Polarity and Proticity
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Dr. Olaf Morawski Prof. Dr. Boleslaw Kozankiewicz Prof. Dr. Andrzej Miniewicz Prof. Dr. Andrzej L. Sobolewski 《Chemphyschem》2015,16(16):3500-3510
A pyrazoline derivative, 3‐(1,1‐dicyanoethenyl)‐1‐phenyl‐4,5‐dihydro‐1H‐pyrazole (DCNP), is studied by using optical spectroscopy methods in several solvents at room and at low temperatures. The DCNP molecule reveals a complex photophysics behavior, which is sensitive to solvent polarity, proticity, temperature and viscosity and arises from the presence of two rotational degrees of freedom of the dicyanovinyl group—the torsion around the double C=C bond and the s‐trans–s‐cis isomerization around the single C?C bond—that differently behave in various environmental conditions. The fluorescence yield of a few percent and sub‐nanosecond decay times observed at room temperature make the compound useful for optical studies of liquid environments. The proticity of polar solvents can be detected with two‐exponential fluorescence decays. At low temperatures, DCNP can be used as solvent viscosity or temperature fluorescent sensor. 相似文献
11.
Novel, multibranched “triphenylamine based donor with added auxiliary methoxy donor and dicyanovinyl acceptor” based fluorescent molecules are developed. The dicyanoisophorone moiety is used as a configurationally locked polyene system for π-conjugation linking between donor and acceptor, to control the unnecessary intramolecular rotations in the molecule, which can to act as a rotor. The synthesized dyes show good fluorescent molecular rotor properties and strong emission solvatochromism. Auxiliary methoxy donors shift both the absorption and emission maxima towards longer wavelengths compared to known analogues, along with increased Stokes shifts. Fluorescent molecular rotor properties of the dyes are influenced by a local excited state to twisted intramolecular charge transfer state transition, which is discussed in terms of emission solvatochromism and Lippert–Mataga, Weller and Rettig polarity plots. Three different viscous solvent systems i.e., paraffin oil–dichloromethane, polyethylene glycol-400–dichloromethane and polyethylene glycol-400–N,N-dimethylformamide are used to investigate the sensitivity of rotors towards the viscosity of the environment. A maximum 16-fold enhancement in emission intensity and 0.616 × value is achieved for rotor Dye-3. The polarity effect of a binary viscous solvent system, by the virtue of intramolecular charge transfer, on the viscosity sensing properties of rotors is explained by constructing the Weller and Rettig’s plots for different viscous systems. 相似文献
12.
Some regularities of the energetics of structure formation in mixtures of polar organic solvents not forming layered structures with liquid hydrocarbons and in mixtures of inert and low-polar diluents at 20
were established. In most cases, the deviation of the methylene group increments from additivity, defining the energy stability of a liquid structure, was distinctly negative. In particular, the increment decreases dramatically from individual higher alcohols to mixtures of propanol and n-octane which model the former in the concentration of functional groups per unit volume, and the structure of mixture is weakened. Solvents of close polarity, in turn, form mixtures whose methylene group increments are well approximated by the additivity law. 相似文献
13.
Elisabeth Kauffmann Jean-Marie Lehn Jean-Pierre Sauvage 《Helvetica chimica acta》1976,59(4):1099-1111
The enthalpies and entropies of complexation of alkali and alkaline-earth metal cations by several macrobicyclic ligands have been obtained from calorimetric measurements and from the previously determined stability constants [2]. Both enthalpy and entropy changes play an important role in the stability and selectivity of the complexes. Particularly noteworthy are the large enthalpies and the negative entropies of complexation obtained for the alkali cation complexes (Na+, K+, Rb+ and Cs+ cryptates). The Sr2+ and Ba2+ as well as [Li+ ? 2.1.1] 1 For use of the symbols see [2]. and [Na+ ? 2.2.1] cryptates are of the enthalpy dominant type with also a favourable entropy change. The Ca2+ and [Li+ ? 2.2.1] cryptates are entirely entropy stabilized with about zero heat of reaction. The high stability of the macrobicyclic complexes as compared to the macromonocylcic ones, the cryptate effect, is of enthalpic origin. The enthalpies of complexation display selectivity peaks, as do the stabilities, whereas the entropy changes do not. The high M2+/M+ selectivities found in terms of free energy, may be reversed when enthalpy is considered in view of the very different role played by the entropy term for M2+ and M+ cations. The enthalpies and entropies of ligation show that whereas the cryptate anions are similar in terms of entropy irrespective of which cation is included, the ligands, despite being more rigid than the hydration shell, are nevertheless able to adjust to some extent to the cation. This conclusion agrees with published X-rays data. The origin of the enthalpies and entropies of complexation is discussed in terms of structural features of the ligands and of solvation effects. 相似文献
14.
报道了应用近年来发展的薄层光谱电化学技术,对几种促进剂(4,4'-二硫基联吡啶、腺嘌呤、L-半胱氨酸)存在下细胞色素C电子迁移过程进行了探讨。 相似文献
15.
The dependence of exciplex emission spectra on the solvent polarity was studied for exciplexes with the Gibbs free energy of excited-state electron transfer, G
*
et
, exceeding –0.1 eV (for pyrene, fluoranthene, 1,12-benzoperylene, and 9-cyanoanthracene with methoxybenzenes or dimethylnaphthalene). These exciplexes showed stronger changes in the spectral shift of exciplex emission and the extent of charge transfer with increasing solvent polarity than the exciplexes having more negative G
*
et
values. The parameters (difference in energy of charge transfer (CT) and locally excited (LE) states in a vacuum, (H
0
22– H
0
11), and the matrix element for electronic coupling of CT and LE states H
12and mrelated to the dipole moment of the CT state and the size of the exciplex) determining the extent of charge transfer, the spectral shift, and other properties of exciplexes were evaluated. The parameters H
12and mfor the exciplexes examined fall in the interval 0.1–0.5 and 1.0–1.7 eV, respectively, and the difference (H
0
22– H
0
11) is proportional to G
*
et
. 相似文献
16.
Fullerelleshavegeneratedarapidlygrowingandactiveresearchareabecauseoftheirunusualstructureandphysico-chemicalproperties.Fullerenes(C,.,.C,,)havehigherelectrollaffinity(2.75ev),soitiswellkllownthattheyareexcellentelectronacceptorsandhavealargenumberofcolljugatedrsbondswhichmayleadtolargenon-linearpolarizabilities'.C,,.,isreportedtoformchargetranstbrcomplexes(CTC)withappropriateelectrondonors,forexample,polymolecularPVK,y-cyclodextrin,aromaticandaliphaticammes'-3.Thecharge-transferinteraction… 相似文献
17.
Dr. Michael J. James Felix Strieth-Kalthoff Frederik Sandfort Felix J. R. Klauck Felicitas Wagener Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(35):8240-8244
The development and application of traceless acceptor groups in photochemical C−C bond formation is described. This strategy was enabled by the photoexcitation of electron donor–acceptor (EDA) complexes with visible light. The traceless acceptors, which were readily prepared from amino acid and peptide feedstocks, could be used to alkylate a wide range of heteroarene and enamine donors under metal- and peroxide-free conditions. The crucial role of the EDA complexes in the mechanism of these reactions was explored through combined experimental and computational studies. 相似文献
18.
T. Madrakian M. Torabbeigi M. A. Zolfigol 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(3-4):177-181
The interaction between tetraethyleneglycol-bis-(8-quinolyl)ether (TEGQ) as a nitrogen and oxygen containing compound as a donor with ICl3 as an acceptor has been investigated spectrophotometrically in chloroform, acetonitrile and dimethyl sulfoxide at different temperatures. The results of mole ratio plots and continuous variation data show the stoichiometry of complexation is 2:1 ICl3/TEGQ. The formation constants of the resulting complexes and thermodynamic parameters have been determined. The results indicate the iodine trichloride complex with TEGQ is enthalpy stabilized but entropy destabilized. 相似文献
19.
Yao Xinding Jinju Ma Ruina Fang Qishan Yuan Wei Liu 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2019,93(12):2340-2348
Russian Journal of Physical Chemistry A - The solubility of R-2[4-(6-chloro-2-benzoxazolyloxy)phenoxy]propanoic acid (abbreviated as Fenoxaprop-P) in acetone, methyl ethyl ketone (MEK),... 相似文献