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1.
Yan Liu Hongchen Du Guixiang Wang Xuedong Gong Lianjun Wang Heming Xiao 《International journal of quantum chemistry》2011,111(5):1115-1126
The density functional theory has been used to study the tautomeric equilibrium of 2‐diazo‐4,6‐dinitrophenol(DDNP) in the gas phase and in 14 solvents at the B3LYP/6‐31G* level. The solvent effects on the tautomeric equilibria were investigated by the self‐consistent reaction field theory (SCRF) based on conductor polarized continuum model (CPCM) in apolar and polar solvents and by the hybrid continuum‐discrete model in protic solvent, respectively. Solvent effects on the computed molecular properties, such as molecular geometries, dipole moments, ELUMO, EHOMO, total energies for DDNP tautomers and transition state, tautomerization energies and solvation energies have been found to be evident. The tautomeric equilibrium of DDNP is solvent‐dependent to a certain extent. The tautomer I (cyclic azoxy form) is preferred in the gas phase, while in nonpolar solvents tautomer I and II (quinold form) exist in comparable amounts, and in highly polar solvents, the tautomeric equilibrium is shifted in favor of the more polar tautomer II . © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
2.
Dr. Matthias Georg Schwab Dr. Tianshi Qin Dr. Wojciech Pisula Dr. Alexey Mavrinskiy Dr. Xinliang Feng Dr. Martin Baumgarten Hun Kim Dr. Frédéric Laquai Sebastian Schuh Roman Trattnig Prof. Emil J. W. List Prof. Dr. Klaus Müllen 《化学:亚洲杂志》2011,6(11):3001-3010
A set of cyclo‐7,10‐tris‐triphenylenyl macrocycles have been prepared by a Yamamoto cyclotrimerization protocol. In these novel macrocycles, three triphenylene units are covalently linked to each other, resulting in the formation of triangular‐shaped molecules. The fully planar derivative revealed pronounced self‐assembly behavior. NMR spectroscopy was used to determine the association constant in solution. 2D wide‐angle X‐ray scattering was applied to the study of the liquid crystallinity of this new discotic mesogen in the bulk state. Furthermore, nonplanar, laterally substituted derivatives were successfully tested as blue emitters in organic light‐emitting diodes owing to their unique optoelectronic properties and their high stability. In this case, substitution with sterically demanding phenyl groups was efficiently used to suppress intermolecular packing, thus preventing undesired quenching effects. 相似文献
3.
The UV and visible spectra of some arylazo barbituric acids and arylazo pyrimidine in pure and mixed organic solvents of varying polarities have been studied. The different absorption bands displayed in the electronic spectra of these compounds are assigned and the possibility of the existence of these compounds in tautomeric equilibrium as well as in intra‐ and intermolecular H‐bonding were examined. The solute‐solvents molecular complexes liable to exist in polar‐nonpolar mixed solvents are investigated. The structure of the azo compounds were confirmed by 1H NMR and IR spectroscopy. The ionization processes of the compounds were investigated and the possible ionization constants were determined and discussed in terms of molecular structure of the azo compounds. 相似文献
4.
带极性侧链的环[6]芳酰胺的球形自组装 总被引:1,自引:0,他引:1
环芳酰胺是一类基于三中心氢键促进,经寡聚前体一步大环合成法得到的刚性大环分子.通过紫外-可见(UV-Vis)光谱、动态光散射(DLS)、扫描电镜(SEM)、透射电镜(TEM)和原子力显微镜(AFM)等实验手段,详细考察了侧链为三甘醇单甲基醚链,由六个苯环单元组成的环[6]芳酰胺的自组装行为.实验结果表明,该大环在1,2-二氯乙烷中发生自组装,其组装聚集体随温度升高产生从聚集体到单分子的解聚变化,至70℃时几乎完全解聚;在由良溶剂(二氯甲烷)和不良溶剂(芳烃类)组成的混合溶剂中,带有三甘醇醚链的环[6]芳酰胺化合物1自组装成微球,结合热稳定性实验和TEM证实是实心微球而非囊泡.进一步发现微球形成和形貌依赖于混合溶剂中不良溶剂的极性和种类,芳烃类溶剂有利于微球形成,而烷烃和极性溶剂则不利,后者更倾向于形成膜的结构. 相似文献
5.
The tautomeric equilibria of a series of 3-hydroxypyridine derivatives including pyridoxal-5'-phosphate (PLP), the active form of vitamin B(6), have been studied using density functional calculations (B3LYP/6-311+G//B3LYP/6-31G) in the gas phase and in different solvents. Three different approaches, namely continuum, discrete, and hybrid (combined discrete/SCRF), were employed to investigate the effects of solvation on the tautomeric equilibria. In all cases, the neutral hydroxy form is significantly more stable than the zwitterionic oxo form (by 43-56 kJ mol(-)(1)) in the gas phase. The tautomeric energies reduce substantially in the presence of a polarizable dielectric medium. However, the neutral form is calculated to be the dominant form in nonpolar and aprotic polar solvents. On the other hand, a reversal of tautomeric equilibrium, in favor of the zwitterionic form, is predicted in an aqueous medium. This study highlights the role of both water molecules and bulk solvent effect in influencing the tautomeric equilibria of the PLP related compounds. A combination of explicit microsolvation and continuum reaction field is required to account fully for the energetic effect of aqueous solvation. The tautomeric free energy differences (deltaG(298)) of PLP in the gas phase and in aprotic polar (epsilon = 40) and aqueous media are predicted to be 47, 22, and -29 kJ mol(-)(1), respectively. 相似文献
6.
Sven Wiesner Dr. Arne Wagner Dr. Elisabeth Kaifer Prof. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10438-10445
We report on the first valence tautomeric dinuclear copper complex, featuring 2,3,5,6‐tetrakis(tetramethylguanidino)pyridine as a bridging redox‐active GFA (guanidino‐functionalized aromatic) ligand. The preferred electronic structure of the complex is massively influenced by the environment. In the solid state and in nonpolar solvents a paramagnetic, dinuclear CuII complex with a neutral GFA ligand is present. In polar solvents, the electronic structure changes to a diamagnetic, dinuclear CuI complex with a twofold‐oxidized GFA ligand. Using acetone as a solvent, both electronic structures are accessible due to a temperature‐dependent equilibrium between the two valence tautomeric complexes. Our results pave the way for a broader use of valence tautomeric transition‐metal complexes in catalytic reactions since anionic coligands can now be tolerated owing to the neutral/positively charged GFA ligand. 相似文献
7.
Synthesis of Phenylene Vinylene Macrocycles through Acyclic Diene Metathesis Macrocyclization and Their Aggregation Behavior
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Dr. Chenxi Zhang Chao Yu Dr. Hai Long Ryan J. Denman Dr. Yinghua Jin Prof. Dr. Wei Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):16935-16940
A series of phenylene vinylene macrocycles (PVMs) bearing substituents with various sizes and electronic properties have been synthesized through a one‐step acyclic diene metathesis macrocyclization approach and their aggregation behaviors have been investigated. In great contrast to the aggregation of the analogous phenylene ethynylene macrocycles, which aggregate only when substituted with electron‐withdrawing groups, these PVMs undergo exceptionally strong aggregation, regardless of the electron‐donating or ‐withdrawing characters of the substituents. The unusual aggregation behavior of the PVMs is further investigated with thermodynamic and computer modeling studies, which show a good agreement with the recently proposed direct through‐space interaction model, rather than the polar/π model. The high aggregation tendency of PVMs suggests the great potential of this novel class of shape‐persistent macrocycles in a variety of applications, such as ion channels, host–guest recognition, and catalysis. 相似文献
8.
Hypericin in organic solvents displays two types of electronic spectra: one type which shows a distinct solvatochromic effect, the stable form, and the other, the unstable form, which lacks this property. The latter type is formed in dry nonprotic solvents (e.g. tetrahydrofuran, EtOAc) and can be converted to the stable form on addition of protic solvents. In order to establish the tautomeric structure of the unstable form we applied conventional nuclear magnetic resonance techniques as well as two-dimensional gradient-enhanced heteronuclear multiple-quantum correlation, gradient-enhanced ROESY and one-dimensional nuclear Overhauser effect difference experiments. All these techniques pointed to the fact that the unstable form has the 7,14-diketo tautomeric structure, like the stable form, and not the 1,6-diketo structure. Electronic spectroscopy indicated that the unstable form has acidic properties and therefore possesses two free OH groups at C3 and C4 at the bay region of the molecule. 相似文献
9.
Detection of Significant Aprotic Solvent Effects on the Conformational Distribution of Methyl 4‐Nitrophenyl Sulfoxide: From Gas‐Phase Rotational to Liquid‐Crystal NMR Spectroscopy
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Prof. Giorgio Celebre Prof. Giuseppina De Luca Dr. Maria Enrica Di Pietro Dr. Barbara Michela Giuliano Prof. Sonia Melandri Dr. Giorgio Cinacchi 《Chemphyschem》2015,16(11):2327-2337
The conformational equilibrium of methyl 4‐nitrophenyl sulfoxide (MNPSO) was experimentally investigated in the gas phase by using microwave spectroscopy and in isotropic and nematic liquid‐crystal solutions, in which the solvents are nonaqueous and aprotic, by using NMR spectroscopy; moreover, it was theoretically studied in vacuo and in solution at different levels of theory. The overall set of results indicates a significant dependence of the solute conformational distribution on the solvent dielectric permittivity constant: when dissolved in low‐polarity media, the most stable conformation of MNPSO proved to be strongly twisted with respect to that in more polar solvents, in which the conformational distribution maximum essentially coincides with that obtained in the gas phase. We discuss a possible explanation of this behavior, which rests on electrostatic solute–solvent interactions and is supported by calculations of the solute electric dipole moment as a function of the torsional angle. This function shows that the least polar conformation of MNPSO is located at a twist angle close to that of the conformational distribution maximum found in less‐polar solvents. This fact, associated with a relatively flat torsional potential, can justify the stabilization of the twisted conformation by the less‐polar solvents. 相似文献
10.
Dipl.‐Chem. Timm Heek Prof. Dr. Frank Würthner Prof. Dr. Rainer Haag 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):10911-10921
Four new water‐soluble polyglycerol‐dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core‐unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core‐unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron‐donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water. 相似文献
11.
O. P. Petrenko V. V. Lapachev I. K. Korobeinicheva V. P. Mamaev 《Chemistry of Heterocyclic Compounds》1987,23(12):1343-1347
The effect of solvents on the position of the azinyl-ylidene tautomeric equilibrium in series of azinylmethanes was studied. It was shown that an increase in the polarity of the solvent leads to stabilization of the ylidene tautomer; the sensitivity of the tautomeric equilibrium to the effects of the solvent depends on the form of the side fragment that undergoes tautomerization. It was concluded that stabilization of the ylidene tautomeric form by polar solvents is a general tendency in series of prototropic equilibrium of the azinyl-ylidene type as a whole.See [1] for Communication 16.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1668–1672, December, 1987. 相似文献
12.
2,6-二巯基吡啶互变异构平衡体系溶剂效应的理论研究 总被引:3,自引:0,他引:3
在气相及甲苯、氯仿、乙腈和水等溶剂中对2,6-二巯基吡啶及其硫酮式互变异构体进行了HF/6-31G**水平上的优化,其中溶液中的计算采用Onsager自洽反应场(SCRF)模型.探讨了溶剂对体系几何结构和能量的影响.结果表明:溶剂的存在与极性的增加有利于平衡体系中硫酮式异构体的存在. 相似文献
13.
Rupashree Balia Singh Subrata Mahanta Nikhil Guchhait 《Journal of photochemistry and photobiology. A, Chemistry》2008,200(2-3):325-333
The possibility of ground and excited state proton transfer reaction across the five member intramolecular hydrogen bonded ring in 4-hydroxyacridine (4-HA) has been investigated spectroscopically and the experimental results have been correlated with quantum chemical calculations. The difference in the emissive behaviour of 4-HA in different types of solvents is due to the presence of different species in the excited state. In non-polar solvents, the species present is non-fluorescing in nature, whereas 4-HA molecule shows normal emission from intramolecularly hydrogen bonded closed conformer in polar aprotic solvents. In polar protic solvents like MeOH, EtOH, etc. (except water), a single broad emission band is attributed to the hydrogen bonded solvated form of 4-HA. However, in case of water, fluorescence from the tautomeric form of 4-HA is observed apart from emission from the solvated form. Emission from the tautomeric form may arise due to double proton transfer via a single water molecule bonded to 4-HA. Evaluation of the potential energy surfaces by quantum chemical calculations using density functional theory (DFT) and time dependent density functional theory (TDDFT), however, points towards the possibility of proton transfer—both intrinsic intramolecular as well as water mediated in the first excited state of 4-HA. 相似文献
14.
Miriana Kfoury David Landy Sophie Fourmentin 《Current Opinion in Green and Sustainable Chemistry》2022
Solvation in deep eutectic solvents (DESs) and encapsulation in macrocycles are efficient strategies for molecule's solubilization. Recently, new systems combining DES and macrocycles are being constructed using two approaches: a) solubilizing hosts in preformed DES or b) using hosts as a DES component. This strategy could evolve in new outcomes in DES properties, more precisely provide the solvents with supramolecular capacity, and translate into interesting performances. In the present review, we will give the reader an overview of the studies accomplished in this growing research area, with a focus on the experimental perspectives that we consider to be the most important in order to enlarge knowledge on the properties and behavior of these neoteric systems. 相似文献
15.
Andrés M. Durantini R. Dario Falcone Dr. Juana J. Silber Prof. N. Mariano Correa Dr. 《Chemphyschem》2009,10(12):2034-2040
Herein, we report a study of the interactions between different nonaqueous polar solvents, namely, ethylene glycol (EG), propylene glycol (PG), glycerol (GY), dimethylformamide (DMF), and dimethylacetamide (DMA), and the polar heads of sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate (AOT) in nonaqueous AOT/n‐heptane reverse micelles. The goal of our study is to gain insights into the unique reverse‐micelle microenvironment created upon encapsulation of these polar solvents. For the first time, the study is focused on determining which regions of the AOT molecular structure are involved in the interactions with the polar solvents. We use FTIR spectroscopy—a noninvasive technique—to follow the changes in the AOT C?O band and the symmetric and asymmetric SO3? vibration modes upon increasing the content of polar solvents in the micelles. The results show that GY interacts through H bonds with the SO3? group, thereby removing the Na+ counterions from the interface remaining in the polar core of the micelles. PG and EG interact through H bonds, mainly with the C?O group of AOT, penetrating into the oil side of the interface. Thus, they interact weakly with the Na+ counterion, which seems to be close to the AOT sulfonate group. Finally, DMF and DMA, encapsulated inside the reverse micelles, interact neither with the C?O nor with the SO3? groups, but their weakly bulk‐associated structure is broken because of the interactions with Na+. We suggest that DMF and DMA can complex the Na+ ions through their carbonyl and nitrogen groups. Hence, our results do not only give insights into how the constrained environment affects the bulk properties of polar solvents encapsulated within reverse micelles but—more importantly—they also help us to answer the tricky question about which regions of the AOT moiety are involved in the interactions with the polar solvents. We believe that our results show a clear picture of the interactions present at the nonaqueous reverse‐micelle interface; this is important because these media are interesting nanoreactors for heterogeneous chemistry, templates for nanoparticles, and models for membranes. 相似文献
16.
Martin Berberich Mirco Natali Peter Spenst Dr. Claudio Chiorboli Prof. Dr. Franco Scandola Prof. Dr. Frank Würthner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(43):13651-13664
A novel, highly stable photochromic dyad 3 based on a perylene bisimide (PBI) fluorophore and a diarylethene (DAE) photochrome was synthesized and the optical and photophysical properties of this dyad were studied in detail by steady‐state and time‐resolved ultrafast spectroscopy. This photochromic dyad can be switched reversibly by UV‐light irradiation of its ring‐open form 3 o leading to the ring‐closed form 3 c , and back reaction of 3 c to 3 o by irradiation with visible light. Solvent‐dependent fluorescence studies revealed that the emission of ring‐closed form 3 c is drastically quenched in solvents of medium (e.g., chloroform) to high (e.g., acetone) polarities, while the emission of the ring‐open form 3 o is appreciably quenched only in highly polar solvents like DMF. The strong fluorescence quenching of 3 c is attributed to a photoinduced electron‐transfer (PET) process from the excited PBI unit to ring‐closed DAE moiety, as this process is thermodynamically highly favorable with a Gibbs free energy value of ?0.34 eV in dichloromethane. The electron‐transfer mechanism for the fluorescence quenching of ring‐closed 3 c is substantiated by ultrafast transient measurements in dichloromethane and acetone, revealing stabilization of charge‐separated states of 3 c in these solvents. Our results reported here show that the new photochromic dyad 3 has potential for nondestructive read‐out in write/read/erase fluorescent memory systems. 相似文献
17.
Ragusa A Rossi S Hayes JM Stein M Kilburn JD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(19):5674-5688
A series of chiral bisthiourea macrocycles 1-4 have been prepared and their binding properties with various dicarboxylate salts have been examined by using NMR titration and isothermal calorimetry experiments. Macrocycle 1, in particular, favours the 1:1 binding of N-protected L-glutamate and aspartate, but favours 1:2 binding of the corresponding D-amino acids in polar solvents (dimethyl sulfoxide and acetonitrile). The macrocycles, however, do not bind carboxylates at all in the less competitive solvent chloroform. The binding properties of these macrocyles are sensitive to small structural changes as demonstrated by the altered binding properties of macrocycles 2-4 compared with 1. 相似文献
18.
The tautomeric properties of isoguanine (also named 2-oxoadenine or 2-hydroxyadenine) have been studied in the gas phase, in different pure solvents, and in the DNA environment using state of the art theoretical methods. Our results show that isoguanine constitutes an unique example of how tautomerism can be modulated by the environment. Compared to the tautomeric preference in the gas phase, both polar solvents and the DNA microenvironment dramatically change the intrinsic tautomeric properties of isoguanine. Tautomers which are important in physiological conditions are less than 1/10(5) of the total population of isoguanine in the gas phase. The impact of the present findings in the understanding of spontaneous mutations and in the design of new nucleobases with multiple recognition properties is discussed. 相似文献
19.
It was shown by quantum chemical methods and 1H NMR spectroscopy that in the series of prototropic tautomeric quinazolin-4-ones with hydrogenated 1,3-diazaheterocycles
annulated at positions 2 and 3, namely, imidazole, pyrimidine, or [1,3]diazepine (compounds 1–3, respectively), the 1H-tautomeric form strongly predominates in the gas phase and in solutions regardless of the nature of these cycles. Tautomerization
of tricycles 1–3 occurs via the intermolecular mechanism to form as intermediates hydrogen-bonded cyclodimers of these compounds or their cyclosolvates
with proton-donor solvents. The key step of the reaction is the intraassociated concerted double proton transfer, which can
proceed in nearly synchronous and asynchronous modes. In particular, double proton transfer in cyclodimers of quinazolinones
1–3 is asynchronous and proceeds with the formation of solvate-stabilized polar transition states, which are similar in structure
to ionic intermediates of the nonconcerted double proton transfer. 相似文献
20.
Pengcheng Jin Feng Tian Yanbing Han Lijiao Wang Xiaohui Zhao Jinchong Xiao 《化学:亚洲杂志》2019,14(23):4395-4399
The instability of large acenes and analogues usually limits their wide potentials in organic devices. Thus, effectively constructing large acenes or heteroacenes and examining their optoelectronic properties are of great interest. We herein describe the synthesis, optoelectronic behaviors and electroluminescent property of dimesitylboryl‐decorated azaarene 5 and its homologue 7 . The former emits strong green fluorescence in non‐polar solvents but yellow light in polar solvents. The latter emits a blue light in various organic solvents. Moreover, their electrochemical behavior, photostability and electroluminescent property were further studied in a comparative manner, and the experimental findings suggest that the desired heteroarenes are appealing materials for fabricating electroluminescent devices. 相似文献