Effect Of Solvent Polarity Research Articles

Interfacing High‐Energy Charge‐Transfer States to a Near‐IR Sensitizer for Efficient Electron Transfer upon Near‐IR Irradiation

AbstractPush–pull systems comprising of triphenylamine–tetracyanobutadiene (TPA‐TCBD), a high‐energy charge‐transfer species, are linked to a near‐IR sensitizer, azaBODIPY, for promoting excited‐state CS. These systems revealed panchromatic absorption owing to intramolecular CT and near‐IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs‐TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA‐TCBD entities in 3 seem to prolong lifetime of the CS state. We have been successful in demonstrating efficient CS upon both high‐energy CT and low‐energy near‐IR excitations, signifying importance of these push–pull systems for optoelectronic applications operating in the wide optical window.

Polymerization mechanism of 1,3-benzoxazine catalyzed by PCl5 and rearrangement of chemical structures

Ring-opening polymerization of benzoxazine monomers is a complex process and various chemical structures including N,O-acetal structures, phenolic Mannich structures and arylamine Mannich structures are formed in polybenzoxazines. To understand the polymerization mechanism, the effects of temperature, time and solvent polarity on the polymerization routes, chemical structures and thermal properties were studied. It was discovered that the N,O-acetal structures and the phenoxy structures can be obtained in a low-polarity solvent like dichloromethane at low temperature (−20 °C) with the aid of PCl5, while the arylamine Mannich structures can be readily generated in polar solvent like N,N-Dimethylformamide at high temperature (>80 °C) in the presence of PCl5. However, the phenolic Mannich structures can be directly formed at high temperature (>180 °C) without any catalysts. Upon prolonging the reaction time or elevating the temperature, the phenoxy structures easily rearranged into the N,O-acetal structures or the arylamine Mannich structures. Further increasing the temperature will cause the arylamine Mannich structures to rearrange into the phenolic Mannich structures and even the phenolic methylene structures. Therefore, both phenoxy structures and N,O-acetal structures showed poor thermal stability; while the arylamine Mannich structures possessed lower initial decomposition temperature but higher char yield compared with the phenolic Mannich structures because of the formation of thermally unstable iminium ions and the anchoring of dangling aniline moieties.

The effect of solvent polarity on the antioxidant potential of echinatin, a retrochalcone, towards various ROS: a DFT thermodynamic study

The antioxidant properties of echinatin (Ech), isolated from liquorice, have recently been reported. It is well known that the free radical species can be deactivated by phenolic antioxidants via different mechanistic pathways. In this work, the scavenging of eighteen different reactive oxygen species (ROS) has been considered, focussing on three main working mechanisms, namely hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). The investigations have been performed in different dielectric media, viz. gas phase, benzene, methanol and aqueous solution, using density functional theory (DFT) calculations at the M05-2X/6-311++G** level. Various molecular descriptors have been elucidated for Ech as well as the ROS and compared with the reference antioxidant molecule, trolox. In addition, the redox potentials and the equilibrium constants have been calculated to discuss the feasibility of the overall scavenging process. The results demonstrate that the 4-OH group is the first site for H-atom donation, followed by 4’-OH. Further, it has been found that HAT would be the most favourable mechanism in the gas phase. The SPLET mechanism is thermodynamically favoured in polar media like water and methanol, while in the case of non-polar solvents like benzene, the two mechanisms are observed to be competitive.

Base Promoted Synthesis of 2-((5-methoxynaphthalen-1-yl)methyl)-3-methyl-5-sec-amino-[1,1′-biphenyl]-4-carbonitrilederivatives: Photophysical, Solvatochromic and DFT studies

Newer, simple and efficient synthesis of 2-((5-methoxynaphthalen-1-yl)methyl)-3-methyl-5-sec-amino-[1,1′-biphenyl]-4-carbonitrile derivatives using ring transformation strategy. The synthesized products were characterized by spectral analysis, fluorescence emission and absorption measurements were studied in various solvents having varying polarity and dielectric constants to find out a change in dipole moment in ground state and excited state of derivatives. Lippert–Mataga plots were utilized to know the effect of solvent polarity on spectral behavior of molecules. The position of the Stokes shifts was found to be depends on specific solute–solvent interactions, playing a vital role in electronic excitation of molecules. A rational relationship is examined between fluorescence quantum efficiencies and calculated HOMO and LUMO energies by DFT calculations. The electrochemical investigation of derivatives was performed by cyclic voltammetry.

An investigation of physicochemical properties of Nigella sativa L. Seed oil from Al-Qassim by different extraction methods

An investigation of physicochemical properties of Nigella sativa seed oil from Al-Qassim, KSA was conducted using cold press and Soxhlet extraction methods. The effect of solvent polarity on the oil components and properties were examined using hexane, tetrahydrofuran, ethanol, dichloromethane, methanol and methanol-water binary system. The results demonstrated a high yield of oil with the Soxhlet method using ethanol (40.16%) while the samples extracted with the methanol–water binary system produced the lowest yield (28.28%). Linoleic acid was the major free fatty acid in all samples followed by oleic and palmitic acids. Moreover, the triacylglycerol analysis was carried out using a high-performance liquid chromatography system. The results revealed that the studied oil samples were rich in unsaturated triacylglycerols mostly as 3 Linoleic acid (LLL) but low in saturated triacylglycerols. Thymoquinone, which is known as a powerful antioxidative and antiradical agent was detected in all samples except the sample extracted with the methanol–water binary system. The effect of solvent polarity and the solvent boiling point was observed through the quantity of the main components of each oil sample even though they are from the same source of seed. This study showed that the aforementioned properties were affected by the polarity of the solvent used during the extraction process.

Investigation of kinetics and mechanistic studies of N-(2-hydroxyethyl)phthalimide by +1 halogen oxidant in acidic medium

Abstract The oxidation of N-(2-hydroxyethyl)phthalimide (NHEP) by chloramine T (CAT) in perchloric acid medium has been investigated iodometrically at 298 K. The stoichiometry of the reaction was found to be 1:2. The oxidation products were identified by LC-MS analysis. Kinetic orders with respect to oxidant, substrate and acid concentrations were determined. Enhancement of rate observed with an increase in acid concentration. Effect of solvent polarity and ionic strength was studied. Addition of p-toluene sulfonamide (reductant) to the reaction mixture has no significant influence on the rate. The active species of the oxidant in acidic medium was ascertained. Plausible mechanistic scheme explaining all of the observed kinetic results have been proposed. The effect of temperature on the reaction rates has also been studied. Activation parameters and thermodynamic quantities were evaluated and discussed. The rate constant of the slow step of the reaction along with the equilibrium constants were also calculated.

Effects of Solvent Polarity on Li-ion Diffusion in Polymer Electrolytes: An All-Atom Molecular Dynamics Study with Charge Scaling.

We herein report an all-atom molecular dynamics study on the role of solvent polarity for Li+ diffusion in polymer electrolytes using PEO–LiTFSI (poly(ethylene oxide)–lithium bis(trifluoromethane)sulfonimide) as a model system. By separating the effect of Tg and the effect of solvent polarity in our simulations, we show that the maximum in the diffusion coefficient of Li+ with respect to the dielectric constant of polymer solvent εp is due to transitions in the transport mechanism. In particular, it is found that the frequent interchain hopping involves the coordination of both PEO and TFSI. This optimal solvating ability of PEO at an intermediate value of εp leads to the fast ion conduction. These findings highlight the synergetic effect of solvent polarity and bond polarity on Li-ion diffusion in solid polymer electrolytes.

Singlet Fission and Electron Injection from the Triplet Excited State in Diphenylisobenzofuran–Semiconductor Assemblies: Effects of Solvent Polarity and Driving Force

Singlet fission has emerged as a promising way to overcome the Shockley-Queisser limit in solar energy conversion devices, and a few studies have claimed proof-of-principle results using dye-sensitized photoelectrodes. However, a detailed understanding of what factors govern the fate of the excited state on mesoporous surfaces is still lacking. Here, we have studied how the excitation progresses into singlet fission, electron injection, or formation of molecular charge separated states in diphenylisobenzofuran derivatives with flexible carbon linkers attached to nanocrystalline mesoporous ZrO2, TiO2, and SnO2 thin films. We show that singlet fission occurs for the molecule attached to ZrO2 films when the assembly is immersed in nonpolar solvents, and that singlet fission is hampered by the formation of a molecular charge separated state in more polar solvents. On TiO2 surfaces, direct electron injection from the singlet excited state outcompetes the singlet fission. Instead, triplet formation occurs via charge recombination from the conduction band of TiO2 in nonpolar solvents. When the molecule is attached to SnO2 films, singlet fission partly outcompetes electron injection from the singlet excited state and the two processes occur in parallel. Subsequent to singlet fission on SnO2, triplet injection into the conduction band of SnO2 is observed. The results presented here provide a detailed picture of the singlet fission dynamics in molecules attached to mesoporous semiconductor surfaces, demonstrating that both the semiconductor substrate as well as the environment around the molecules have a large impact, which can be useful in the design of future devices.

Linear and nonlinear optical properties of human hemoglobin.

In this study, we investigated the possibility of interactions between the solvent molecules with the Heme group in the human hemoglobin. The results of this study answer a key question: whether the interactions of the Heme unit with its surroundings are interdependent or independent of the protein units of human hemoglobin. Contributions of the intermolecular interactions were determined by exploiting the solvatochromism spectroscopic data by Kamlet-Taft (KAT) polarity functions. Solvent polarity effects on the nonlinear properties of the Heme's groups in the human hemoglobin (Hb) were investigated via the Z-scan method. The experimental results obtained with spectroscopic and nonlinear optical parameters (absorption coefficient and refractive index) show that the mechanism of solvation and the interactions of Heme are controlled by suitable configuration of the protein units of hemoglobin. In other words, interactions of the Heme with α- and β-globins are an effective factor in controlling the optical behavior of Heme.

Density Functional Theory Studies on the Antioxidant Mechanism and Electronic Properties of Some Bioactive Marine Meroterpenoids: Sargahydroquionic Acid and Sargachromanol.

Certain meroterpenoids isolated from brown alga of the genus Sargassum are known to be antioxidant agents. Herein, density functional theory has been performed to analyze the preferred antioxidant mechanism of the two reactive antioxidant compounds derived from the Sargassum genus, that is, Sargahydroquinoic acid and Sargachromanol and some of their derivatives. Their global reactivity descriptors have been calculated to reveal their reactivity as an antioxidant. Molecule 1 is the most reactive antioxidant according to calculated descriptors. The results of molecule 1 are comparable to that of Trolox, suggesting their similar activity. The calculated descriptors are closely matched with experimental pieces of evidence. It has been found that hydrogen atom transfer (HAT) is more favored in gas media. Also, the effect of solvent polarity on the antioxidant activity has been explored for molecule 1. The results disclose that the polarity of the solvent increases the contribution of two other mechanisms, that is, single-electron transfer, followed by proton transfer and sequential proton loss electron transfer.

Role of the Processing Solvent on the Electrical Conductivity of PEDOT:PSS

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most studied conductive polymers, holding great potential in many applications such as thermoelectric generators, solar cells, and memristors. Great efforts have been invested in trying to improve its mechanical and electrical properties and to elucidate the structure–property relationship. In this work, a systematic and quantitative study of the effect of solvent polarity and solution processing on the film structure and conductivity is presented. By using grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) together with atomic force microscopy (AFM), the importance of the quality of the PEDOT crystal packing is highlighted as a key factor to reach improved electrical conductivity, rather than the overall degree of crystallinity. Moreover, the (re)structuring mechanisms occurring during the film formation and film exposure processes are also studied by in situ GIWAXS. Different intermediate precursor stages and different pathways to reach improved crystallinity are reported depending on the used solvent. The structural results are interpreted looking at the solvent nature and the PSS/solvent affinity. With this contribution, a guidance is hoped to be given not only on how to improve the PEDOT:PSS electrical conductivity, but also on how to tune the film structural or electrical property for different applications.

Solvent polarity effects on thermochemical and NMR parameters of spilanthol pharmacological agent: an experimental and DFT investigation

Through experimental and appropriate quantum chemical approaches, we perform a systematic investigation of the solvent effects on thermochemical and nuclear magnetic resonance (NMR) parameters of (2E,6Z,8E)-N-isobutyl-2,6,8-decatrienamide (spilanthol). The NMR parameters linked to the hydrophobic part of spilanthol present insignificant environmental dependence. However, spin-spin coupling constants such as 1JCO, 1JCN, and 1JNH associated with the amine and active carbonyl sites suffer strong solvent effects of ca. 17%. The 17O shielding constants show the highest sensitivity concerning the solvent polarity, ca. 71%, indicating that oxygen is an appropriate probe for structural characterization. However, the results suggest that the structural changes are partly responsible for these effects, and the significant contribution comes from solute polarization. For polar environments, the NMR parameters become invariant regarding the solvent polarity, which suggests that spilanthol stabilizes better in polar surroundings. These results show that the participation of the solvent is fundamental for a series of effects concerning the stability of the compound. For instance, the analysis of the enthalpy, electronic, and Gibbs free energies suggests that spilanthol is more stable when solvated in organic solvents of moderate dielectric constant, which can improve the extraction process of the compound. Moreover, quantum mechanical calculations performed using self-consistent-charge density-functional based on tight-binding methods considering explicit solvent molecules indicated that the energetic yield obtained in ethanol is higher than that in water solution. The used protocol shows that the energetic and structural parameters of spilanthol are strongly disturbed by the environment and allow to predict accurately its behavior.

Effect of solvent polarity during electrodeposition of asphaltenes from a Colombian oil in the presence of a magnetic field and magnetic nanoparticles

This work focuses on analyzing the electrokinetic behavior of asphaltenes of extra heavy oil. For this, electrodepositions were carried out in asphaltene solutions (4 %w/w) with two solvents of different polarities: toluene and chloroform. In addition, we worked with different magnetic fields, and the effect of adding 1% w/w of magnetic nanoparticles was analyzed. The asphaltenes were extracted with heptane and were characterized by infrared and ultraviolet visible spectroscopy. In the case of toluene, the initial adsorption (without fields) was 4 mg in both anode and cathode. By using an electric field (100 V/m) the deposits increased to 6 mg (anode) and 5 mg (cathode). However, when using a static magnetic field of 0.1 mT, no changes were observed. But, by modifying said field by a dynamic one (0.1 mT and 60 Hz), 15 mg (anode) and 19 mg (cathode) were obtained. Moreover, the addition of nanoparticles (previously characterized by scanning electron microscopy and X ray diffraction) changed the behavior, worsening in the absence of fields, and improving only in the presence of the dynamic field (104 mg, 26 mg in anode and cathode, respectively). Similar results were obtained when using chloroform. Thus, the best performance was obtained by using a dynamic magnetic field. By not considering the nanoparticles, total deposits increased more than 14 times (102 mg versus 7 mg). However, considering them, the increase was greater than 30 times (302 mg versus 10 mg). Therefore, we consider that adding nanoparticles, and supporting the electrodeposition process with a dynamic magnetic field, is an alternative that must be included to improve process performance.

The effects of amino acid sequence and solvent polarity on the self-assembling of cyclic peptide nanotubes and molecular channel formation inside the lipid bilayer

In this article, the effects of amino acid sequence and solvent polarity on the self-assembling process of cyclic peptides (CPs) were investigated by employing molecular dynamic (MD) simulations and quantum chemistry calculations. As a result, CP dimers are not stable in water, because of hydrogen bond (H-bond) lost between the CP units, while chloroform increases the stability of the CP dimers. MM-PBSA and MM-GBSA calculations confirmed that solvent polarity has an important effect on the stability of the CP dimers. Dynamical behavior of the cyclic peptide nanotubes (CPNTs) in chloroform indicates that CPNTs composed of leucine and phenylalanine are better molecular containers than that of isoleucine. At the next step, the ability of these CPNTs in molecular channel formation inside a fully hydrated DMPC (dimyristoylphosphatidylcholine) bilayer was investigated during 50 ns MD simulations. The obtained results show that only CPNT composed of isoleucine can form a molecular channel inside the DMPC membrane because isoleucine has a greater hydrophobicity than leucine and phenylalanine. This property increases the interactions between the CPNT and lipid residues, which elevates the stability of the CPNT inside the DMPC bilayer. Quantum chemistry calculations and non-covalent interactions analysis indicate that the solvent changes the stability and dynamical behavior of the CPNTs through the change in the H-bond strength. Finally, according to the different analyses, it can be concluded that the amino acid sequence in the CP units has an important role in designing specific nanostructures.

Mesoporous rGO@ZnO composite: Facile synthesis and excellent water treatment performance by pesticide adsorption and catalytic oxidative dye degradation

This study describes the facile fabrication, characterization and applications of mesoporous reduced graphene oxide@zinc oxide (rGO@ZnO) composite for the adsorptive removal of the toxic organophosphorus pesticide chlorpyrifos (CPF) and catalytic oxidative degradation of the crystal violet (CV) dye from their respective aqueous solutions. The physical properties of the as-synthesized composite were evaluated by various state of the art techniques like powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The adsorption efficacy of the rGO@ZnO composite was evaluated by conducting adsorption isotherm studies, kinetics studies and thermodynamic studies. The effect of solution pH, adsorbent dosage, solvent polarity, contact time and regeneration ability of the adsorbent on the adsorptive removal efficiency were also studied. Excellent removal efficiency of 95.4% was achieved within 70min of contact time with the rGO@ZnO composite and more than 75% of the pesticide was adsorbed at the end of the fifth adsorption cycle. Batch adsorption results fitted well with the Freundlich adsorption isotherm with a high coefficient of determination (R2). The adsorption kinetics was best described by a pseudo-second-order model with an R2 value of 0.93. Thermodynamic parameters corroborate the physisorption nature of the adsorption owing to the spontaneous and exothermic adsorption process. Pesticide contaminated water was used to determine the field applicability of the rGO@ZnO composite. The catalytic efficiency was evaluated by the oxidative dye degradation performance of rGO@ZnO based on the activation of oxone to produce sulfate radicals which degraded the CV dye within 30min. Results indicate that mesoporous rGO@ZnO is an excellent candidate and possesses huge potential in water treatment.

Blue Highly Fluorescent Boranil Derived From Anil Ligand: Synthesis, Characterization, Experimental and Theoretical Evaluation of Solvent Effect on Structures and Photophysical Properties

In this study, we report the design and the synthesis of a Schiff base; Anil and its corresponding Boron Difluoride complexe; Boranil. The synthesis procedure was carried out adopting new, optimized reaction conditions. The Boranil dye presents the advantage to be emissive in solution. 1H and 19F NMR along with FTIR confirmed both compound's structure. To gain a better understanding of the solvatochromic behavior of Anil and Boranil, the dependence of the absorption spectra on the solvent's polarity was studied in depth. Thus, UV–Vis spectroscopy was performed in five selected solvents. In addition to the solvent's polarity effect, the influence of BF2 moiety introduction on the molecule's photophysical properties was also evaluated. When examining different absorption spectra, we found that the title fluorescent dye exhibited weak solvatochromic (11 nm in THF) as well as a slight redshift broader and relatively more structured absorption spectra after complexation. Besides, we investigate the obtained key structure–property relationships through DFT and TD‐DFT calculations using a 6–311++ G (d, p) basis set. Quantum chemical calculations allowed confirming proposed structures and understanding their electronic structure in larger details. Theoretical results also showed good agreement with the experimental findings. Finally, the frontier molecular orbitals were investigated to illustrate the pi‐conjugation and charge transfer effect.

Solvent polarity sensitive characteristics of various tautomers of azo compounds: Linear and nonlinear optical properties.

Solvents as complex environments can induce considerable effects on the physical, chemical and biological properties of solute molecules. In this work, solvent polarity sensitive characteristics of two tautomers of different azo compounds were studied by using of spectroscopic and Z-scan techniques. In this case, nature and various molecular interactions contribution on the spectral behaviors of azo and hydrazone forms of selected samples were investigated by Kamlet-Abboud-Taft and Catalan models. Moreover, the obtained results of Z-scan indicate that self-defocusing, saturable and reverse saturable absorption features of azo dyes depend highly on substituents and molecular environment polarity characteristic. In this case, media polarity properties have the same effects on the third order nonlinear absorption coefficient and nonlinear refractive index values. Therefore, by measuring one of the third order nonlinear optical coefficients, it is possible to predict solvent polarity effects on the other nonlinear optical coefficient. The calculated dipole moments with high values in the molecular excited state also reveal the probability of molecular charge transfer characteristics. In this case, by excitation process, sample I indicate high dipole moment values in comparison to other samples. Therefore, the results can give useful information about the application of selected samples for designing various optical devices.

TADF Dye-Loaded Nanoparticles for Fluorescence Live-Cell Imaging.

Thermally activated delayed fluorescence (TADF) molecules offer nowadays a powerful tool in the development of novel organic light emitting diodes due to their capability of harvesting energy from non-emissive triplet states without using heavy-metal complexes. TADF emitters have very small energy difference between the singlet and triplet excited states, which makes thermally activated reverse intersystem crossing from the triplet states back to the singlet manifold viable. This mechanism generates a long-lived delayed fluorescence component which can be explored in the sensing of oxygen concentration, local temperature, or used in time-gated optical cell-imaging, to suppress interference from autofluorescence and scattering. Despite this strong potential, until recently the application of TADF outside lighting devices has been hindered due to the low biocompatibility, low aqueous solubility and poor performance in polar media shown by the vast majority of TADF emitters. To achieve TADF luminescence in biological media, careful selection or design of emitters is required. Unfortunately, most TADF molecules are not emissive in polar media, thus complexation with biomolecules or the formation of emissive aggregate states is required, in order to retain the delayed fluorescence that is characteristic of these compounds. Herein, we demonstrate a facile method with great generalization potential that maintains the photophysical properties of solvated dyes by combining luminescent molecules with polymeric nanoparticles. Using an established swelling procedure, two known TADF emitters are loaded onto polystyrene nanoparticles to prepare TADF emitting nanomaterials able to be used in live-cell imaging. The obtained particles were characterized by optical spectroscopy and exhibited the desired TADF emission in aqueous media, due to the polymeric matrix shielding the dye from solvent polarity effects. The prepared nanoparticles were incubated with live human cancer cells and showed very low cytotoxicity and good cellular uptake, thus making fluorescence microscopy imaging possible at low dye concentrations.

Activation of graphitic carbon nitride by solvent-mediated supramolecular assembly for enhanced hydrogen evolution

Developing earth-abundant photocatalysts with high activity and long term-stability for solar-driven hydrogen evolution reaction (HER) is an old but still tough challenge in the photocatalytic water splitting. Despite the remarkable progress that has been made in the preparation and modification of graphitic carbon nitride (g-C3N4), the most popular metal-free photocatalyst, there still exists a need to explore novel synthetic approaches for the controllable synthesis of g-C3N4-based photocatalytic materials toward improved HER performance. Herein, we propose a solvent-mediated supramolecular assembly approach to fabricate modified g-C3N4 nanoarchitectures based on the asymmetric polymerization of three precursors, melamine, cyanuric acid and barbituric acid. The resulting g-C3N4 nanostructure assisted by the supramolecular preorganization of precursors is favorable for visible light harvesting, charge carrier separation and solar HER performance. The hydrogen-evolution rate of the modified g-C3N4 sample derived from ethanol is three times higher than that of g-C3N4 calcined from the symmetric polymerization of melamine and cyanuric acid, implying the important role of barbituric acid. More importantly, the effects of solvent polarity on the morphology, composition, charge carrier dynamics and HER activity were evaluated.

Effect of Solvent Polarity on Enthalpies of Solvation of Ethylene Oxide Oligomers

The enthalpies of dissolution, ΔsolHm∞, and solvation, ΔsolvHm∞, of ether oligomers CH3O(CH2CH2O)nCH3 (n = 1–4) in ethyl acetate, pyridine, N,N-dimethylformamide, and acetonitrile have been determi...