Showing papers on "Solvent effects published in 2016"
TL;DR: A holistic view of solvent effects, the mechanistic elucidation of these effects, and the careful consideration of the challenges associated with solvent use could assist researchers in choosing and designing improved solvent systems for targeted biomass conversion processes.
Abstract: Transforming lignocellulosic biomass into fuels and chemicals has been intensely studied in recent years. A large amount of work has been dedicated to finding suitable solvent systems, which can improve the transformation of biomass into value-added chemicals. These efforts have been undertaken based on numerous research results that have shown that organic solvents can improve both conversion and selectivity of biomass to platform molecules. We present an overview of these organic solvent effects, which are harnessed in biomass conversion processes, including conversion of biomass to sugars, conversion of sugars to furanic compounds, and production of lignin monomers. A special emphasis is placed on comparing the solvent effects on conversion and product selectivity in water with those in organic solvents while discussing the origins of the differences that arise. We have categorized results as benefiting from two major types of effects: solvent effects on solubility of biomass components including cellulose and lignin and solvent effects on chemical thermodynamics including those affecting reactants, intermediates, products, and/or catalysts. Finally, the challenges of using organic solvents in industrial processes are discussed from the perspective of solvent cost, solvent stability, and solvent safety. We suggest that a holistic view of solvent effects, the mechanistic elucidation of these effects, and the careful consideration of the challenges associated with solvent use could assist researchers in choosing and designing improved solvent systems for targeted biomass conversion processes.
304 citations
TL;DR: In this paper, the role of solvents in catalysis is considered from a mechanistic approach and they focus mainly on hydrogenation reactions and cross-coupling reactions.
229 citations
TL;DR: This Highlight is devoted to showcasing the exceptional potential of fluorinated alcohols in the C–H activation field.
Abstract: Fluorinated solvents like 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE) have recently emerged as a remarkable synthetic solution allowing challenging C–H activation reactions. A beneficial effect of these solvents on reactivity, as well as site- and stereoselectivity of various direct functionalization reactions has been observed. Moreover, several catalytic systems specifically require such fluorinated medium. This Highlight is devoted to showcasing the exceptional potential of fluorinated alcohols in the C–H activation field.
149 citations
TL;DR: In this article, a hole-conductor-free fully printable perovskite solar cells with pristine MAPbI 3 via one-step deposition was systematically studied on the hole.
137 citations
TL;DR: This study demonstrated the first successful example of an energy conversion scheme using carbon nitride through photocatalytic CO2 reduction, and polymeric Ru species, which were formed in situ from RuCP on C3N4 under irradiation in a solvent having a high donor number, were active catalysts for CO formation.
Abstract: Photocatalytic CO2 reduction using hybrids of carbon nitride (C3N4) and a Ru(II) complex under visible light was studied with respect to reaction solvent. Three different Ru(II) complexes, trans(Cl)-[Ru(X2bpy) (CO)2Cl2] (X2bpy = 2,2′-bipyridine with substituents X in the 4-positions, X = COOH, PO3H2, or CH2PO3H2), were employed as promoters and will be abbreviated as RuC (X = COOH), RuP (X = PO3H2), and RuCP (X = CH2PO3H2). When C3N4 modified with a larger amount of RuCP (>7.8 μmol g–1) was employed as a photocatalyst in a solvent having a relatively high donor number (e.g., N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) with the aid of triethanolamine (TEOA) as an electron donor, the hybrid photocatalyst exhibited high performance for CO2 reduction, producing CO and HCOOH with relatively high CO selectivity (40–70%). On the other hand, HCOOH was the major product when RuC/C3N4 or RuP/C3N4 was employed regardless of the loading amount of the Ru(II) complex and the...
110 citations
TL;DR: A quantitative thermodynamic model is developed that reveals that the conformation entropy of the n-alkanoate chain released in dissolution greatly stabilize the colloidal solution but the strong chain-chain interdigitation between adjacent particles in solid diminishes the solubility.
Abstract: CdSe-stearates nanocrystal-ligands complex as a whole possess strongly temperature- and size-dependent yet well-defined solubility in small organic solvents, which shows little solvent effects as long as the complexes remained intact. A quantitative thermodynamic model is developed to describe such solubility behavior, which differs fundamentally from conventional models for micron colloids. The model reveals that the conformation entropy of the n-alkanoate chain released in dissolution greatly stabilize the colloidal solution but the strong chain-chain interdigitation between adjacent particles in solid diminishes the solubility. These understandings result in "entropic ligands" (see full disclosure in another report (10.1021/acs.nanolett.6b00730)) as the universal means to battle processability challenges of colloidal nanocrystals.
82 citations
TL;DR: In this article, three triazoles compounds used as corrosion inhibitors for copper in acidic medium, namely: 1,2,4 triazole (TR), 3-amino 1, 2, 4 triazolamide (3 ATR), and 3-5-diamino (3, 5 DATR), have been studied theoretically in order to investigate the correlation between its molecular reactivity indicators and the corresponding inhibition efficiency.
80 citations
68 citations
TL;DR: Urea-LiCl DES was used successfully as a reaction medium in the anionic functionalization of wood cellulose with succinic anhydride and revealed that the DES was a nondegrading and nondissolving reaction medium.
Abstract: Deep eutectic solvents (DESs) are green chemicals that have the potential to replace traditional solvents in chemical reactions. In this study, urea-LiCl DES was used successfully as a reaction medium in the anionic functionalization of wood cellulose with succinic anhydride. The effects of reaction temperature and time on the carboxyl content and yield were evaluated. The analyses of the degree of polymerization and crystallinity revealed that the DES was a nondegrading and nondissolving reaction medium. Three samples with the highest carboxyl contents were further nanofibrillated with a microfluidizer to diameters of 2-7 nm, as observed by atomic force microscopy. Samples treated at 70-80 °C for 2 h gave the best outcome and resulted in highly viscose and transparent gels. The sample treated at 90 °C contained larger nanoparticles and larger aggregates owing to the occurrence of possible side reactions but resulted in better thermal stability.
65 citations
TL;DR: The experimental results reveal that H2O as the solvent could effectively achieve the C-N bond cleavage to produce sulfonamides due to H 2O participating in the reaction process where H2 O plays a dual role.
60 citations
TL;DR: This review describes the structural and catalytic properties of DNA and RNA oligonucleotides in organic solutions and in aqueous solutions with organic cosolvents and will serve as a guide for the selection of solvent systems based on the purpose of the nucleic acid-based experiments.
Abstract: Organic solvents and apolar media are used in the studies of nucleic acids to modify the conformation and function of nucleic acids, to improve solubility of hydrophobic ligands, to construct molecular scaffolds for organic synthesis, and to study molecular crowding effects. Understanding how organic solvents affect nucleic acid interactions and identifying the factors that dominate solvent effects are important for the creation of oligonucleotide-based technologies. This review describes the structural and catalytic properties of DNA and RNA oligonucleotides in organic solutions and in aqueous solutions with organic cosolvents. There are several possible mechanisms underlying the effects of organic solvents on nucleic acid interactions. The reported results emphasize the significance of the osmotic pressure effect and the dielectric constant effect in addition to specific interactions with nucleic acid strands. This review will serve as a guide for the selection of solvent systems based on the purpose of the nucleic acid-based experiments.
TL;DR: In this article, solvent effects on the electronic structure properties of a tryptophan hybrid with Pd doped single walled carbon nanotubes as a new novel biosensor were investigated.
Abstract: Carbon nanotubes and amino acids have a high potential to offer specific advantages as the transducer and the recognition elements of biosensors. Their compatible size with biological structures makes them suitable as implantable sensors. In this work solvent effects on the electronic structure properties of a tryptophan hybrid with Pd doped single walled carbon nanotubes as a new novel biosensor were investigated. As the chemical reaction of a nanobiosensor is affected by the nature of the solvents, 5 different solvents, water, DMSO, ethanol, acetone and carbon tetrachloride are employed to study the role of the solvent polarity on the molecular stability, the optimized geometry and charge distribution of Try/Pd-SWCNT nanobiosensor. To derive the optimized geometries, the density functional theory computations were performed at the B3LYP level with the 6-31G(d) basis set. In addition, the molecular orbital calculations such as natural bond orbitals (NBOs), HOMO–LUMO energy gap, mapped molecular electrostatic potential (MEP) surface and density of state (DOS) were also performed. The results show that the presence of a solvent lowers the HOMO and LUMO energy level and increases or decreases the HOMO–LUMO energy gap depending on the chemical system. Different nucleophile and electrophile sites were detected in the molecular electrostatic maps. The softer investigated biosensors were found in more polar media. The highest reorganization energies for the nanobiosensor resulted in water media. The Trp/Pd/SWCNT presents high stability with considerable values of charge transfer, stabilization energies and the energy bond gap in polar medium which confirm both in vitro and in vivo biosensing applications.
TL;DR: A series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs are reviewed to emphasize the importance of the inclusion of the bulk solvent effects and the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively.
Abstract: Vibrational optical activity spectroscopies, namely vibrational circular dichroism (VCD) and Raman optical activity (ROA), have been emerged in the past decade as a powerful spectroscopic tool for stereochemical information of a wide range of chiral compounds in solution directly. More recently, their applications in unveiling solvent effects, especially those associated with water solvent, have been explored. In this review article, we first select a few examples to demonstrate the unique sensitivity of VCD spectral signatures to both bulk solvent effects and explicit hydrogen-bonding interactions in solution. Second, we discuss the induced solvent chirality, or chiral transfer, VCD spectral features observed at the water bending band region in detail. From these chirality transfer spectral data, the related conformer specific gas phase spectroscopic studies of small chiral hydration clusters, and the associated matrix isolation VCD experiments of hydrogen-bonded complexes in cold rare gas matrices, a general picture of solvation in aqueous solution emerges. In such an aqueous solution, some small chiral hydration clusters, rather than the chiral solutes themselves, are the dominant species and are the ones who contribute mainly to the experimentally observed VCD features. We then review a series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs to emphasize the importance of the inclusion of the bulk solvent effects. These experimental data and the associated theoretical analyses are the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively. We present several approaches to identify and build such representative chiral hydration clusters. Recent studies which applied molecular dynamics simulations and the subsequent snapshot averaging approach to generate the ROA, electronic CD, and optical rotatory dispersion spectra are also reviewed. Challenges associated with the molecular dynamics snapshot approach are discussed and the successes of the seemingly random “ad hoc explicit solvation” reported before are also explained. To further test and improve the “clusters-in-a-liquid” model in practice, future work in terms of conformer specific gas phase spectroscopy of sequential solvation of a chiral solute, matrix isolation VCD measurements of small chiral hydration clusters, and more sophisticated models for the bulk solvent effects would
TL;DR: The first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear velocity perturbation theory (NVPT) derived electronic currents is reported, finding excellent agreement with the theoretical and experimental references.
Abstract: We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear velocity perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liquid phase. At low temperatures, we recover the established double harmonic approximation. The methodology is applied to chiral molecules ((S)-d2-oxirane and (R)-propylene-oxide) in the gas phase and in solution. We find an excellent agreement with the theoretical and experimental references, including the emergence of signals due to chirality transfer from the solute to the (achiral) solvent.
TL;DR: A simple and reliable method based on the inhibited autoxidation of water/THF mixtures, which is calibrated against pulse radiolysis is described, which indicates the occurrence of a SPLET-like mechanism in water.
Abstract: The reactions of alkylperoxyl radicals with phenols have remained difficult to investigate in water. We describe herein a simple and reliable method based on the inhibited autoxidation of water/THF mixtures, which we calibrated against pulse radiolysis. With this method we measured the rate constants kinh for the reactions of 2-tetrahydrofuranylperoxyl radicals with reference compounds: urate, ascorbate, ferrocenes, 2,2,5,7,8-pentamethyl-6-chromanol, Trolox, 6-hydroxy-2,5,7,8-tetramethylchroman-2-acetic acid, 2,6-di-tert-butyl-4-methoxyphenol, 4-methoxyphenol, catechol and 3,5-di-tert-butylcatechol. The role of pH was investigated: the value of kinh for Trolox and 4-methoxyphenol increased 11- and 50-fold from pH 2.1 to 12, respectively, which indicate the occurrence of a SPLET-like mechanism. H(D) kinetic isotope effects combined with pH and solvent effects suggest that different types of proton-coupled electron transfer (PCET) mechanisms are involved in water: less electron-rich phenols react at low pH by concerted electron-proton transfer (EPT) to the peroxyl radical, whereas more electron-rich phenols and phenoxide anions react by multi-site EPT in which water acts as proton relay.
TL;DR: In this paper, the self-consistent reaction field theory was used to investigate the solvent effects on the structure and electronic properties of the hybride of Pd doped single-walled carbon nanotube (Pd/SWCNT) and histidine amino acid as a new generation of nanobiosensors.
TL;DR: The incorporation of a small amount of coordinating PPh2 groups into the copolymer resulted in a chiral macromolecular ligand, which allowed the enantioselective synthesis of both enantiomeric products in an asymmetric Suzuki-Miyaura coupling reaction from a single catalyst.
Abstract: Random poly(quinoxaline-2,3-diyl) copolymers, containing chiral (S)-3-octyloxymethyl and achiral propoxymethyl side chain units, experience an abnormal sergeants-and-soldiers effect, that is, they adopt, depending on the chiral monomer mole fraction, either P- or M-helical conformations in anisole (PhOCH3) and benzotrifluoride (PhCF3). In benzene (PhH) and toluene (PhCH3), these copolymers exclusively adopt an M-helical conformation, regardless of the chiral monomer mole fraction. For a co-300mer, with a 40% mole fraction of chiral units, the selective induction of an M-helix (>99%) was observed in PhH, while in PhCF3, a P-helical conformation was induced selectively (>99%). This helix inversion of the polymer backbone is thus able to control the chirality of a chiral polymer ligand in aromatic solvents. The incorporation of a small amount of coordinating PPh2 groups into the copolymer resulted in a chiral macromolecular ligand, which allowed the enantioselective synthesis of both enantiomeric products in...
TL;DR: In this article, a new excited-state intramolecular proton transfer (ESIPT) fluorophore, 2,4,6-trisbenzothiazolylphenol (4), was synthesized and its photophysical properties were studied with steady state absorption and emission spectroscopy as well as time-dependent density functional theory calculation.
TL;DR: It was found that the higher total interaction energy in PILs results from the strong and directional hydrogen bonds between cation and anion, whereas the larger vaporization enthalpies of AILs clearly arise from increasing dispersion forces between ion pairs.
Abstract: It is well known that gas-phase experiments and computational methods point to the dominance of dispersion forces in the molecular association of hydrocarbons. Estimates or even quantification of these weak forces are complicated due to solvent effects in solution. The dissection of interaction energies and quantification of dispersion interactions is particularly challenging for polar systems such as ionic liquids (ILs) which are characterized by a subtle balance between Coulomb interactions, hydrogen bonding, and dispersion forces. Here, we have used vaporization enthalpies, far-infrared spectroscopy, and dispersion-corrected calculations to dissect the interaction energies between cations and anions in aprotic (AILs), and protic (PILs) ionic liquids. It was found that the higher total interaction energy in PILs results from the strong and directional hydrogen bonds between cation and anion, whereas the larger vaporization enthalpies of AILs clearly arise from increasing dispersion forces between ion pairs.
TL;DR: In this article, a metal ion-sensitive fluorescent probe based on the BODIPY platform with di(2-picolyl)amine as chelator has been synthesized and spectroscopically and photophysically characterized.
Abstract: A novel metal ion-sensitive fluorescent probe – 4,4-difluoro-8-(4-methylphenyl)-5-(phenylethynyl)-3-[bis(pyridin-2-ylmethyl)amino]-4-bora-3a,4a-diaza-s-indacene – based on the BODIPY platform with di(2-picolyl)amine as chelator has been synthesized and spectroscopically and photophysically characterized. The generalized treatment of the solvent effect shows that solvent dipolarity is primarily responsible for the observed shifts of the absorption and fluorescence emission maxima. Complex formation with various metal ions is investigated in acetonitrile solution by means of spectrophotometric and fluorometric titrations. The BODIPY indicator forms 1 : 1 complexes with several transition metal (Ni2+, Cu2+, Zn2+) and heavy metal (Cd2+, Hg2+) ions, producing large bathochromic shifts in the absorption and fluorescence spectra and, except for Ni2+, cation-induced fluorescence amplifications. The dissociation constants of the metal ion complexes range from 4 μM for Hg2+ to 48 μM for Zn2+.
TL;DR: In this article, the synthesis of copper-doped polyaniline was performed in the following solvents: H 2 O, DMF, DO, THF, ACTN and ACN, and then the solvent effects on the formation of NPANI-Cu-X (X represents the dopants, I − and BF 4 − ) were investigated.
TL;DR: In this paper, a method for TMS solvent selection based on quantum chemical predictions of catalyst solubility and phase equilibrium is presented, which allows for solvent effects on the catalyst to be incorporated directly into the solvent screening process.
Abstract: One method that has shown much promise due to its simplicity and effectiveness in homogeneous catalyst recovery is the use of thermomorphic solvent systems (TMS). In this contribution, a novel method for TMS solvent selection based on quantum chemical predictions of catalyst solubility and phase equilibrium is presented. This allows for solvent effects on the catalyst to be incorporated directly into the solvent screening process. A framework for TMS design is developed and implemented using the hydroformylation of 1-dodecene and the rhodium-Biphephos catalyst as an example reaction system. In this way, several promising TMS systems were identified. Experiments were then performed to validate the model based on catalyst partitioning and phase equilibrium. This was followed by conducting a series of reactions to investigate feasibility of the new TMS systems in the actual hydroformylation. In the end it was shown that although some problems arise from inconsistencies in phase equilibrium predictions, the method does provide a functioning a priori basis for TMS development.
TL;DR: In this paper, a bio-oil was subjected to hydrodeoxygenation (HDO) reactions with polar protic (ethanol), polar aprotic (acetone), and nonpolar (ether) solvents in the presence of Pt/C catalyst.
TL;DR: In this article, the authors investigated six anion-molecule nucleophilic substitution reactions in methanol and dipolar aprotic solvents, and showed that the SMD model is not adequate for dipolar anion to dipolar acid solvent rate acceleration effect.
Abstract: In the past seven years, the SMD (Solvent Model Density) method has been widely used by computational chemists. Thus, assessment on the reliability of this model for modeling chemical process in solution is worthwhile. In this report, it was investigated six anion-molecule nucleophilic substitution reactions in methanol and dipolar aprotic solvents. Geometry optimizations have been done at SMD/X3LYP level and single point energy calculations at CCSD(T)/TZVPP + diff level. Our results have indicated that the SMD model is not adequate for dipolar aprotic solvents, with a root of mean squared (RMS) error of 5.6 kcal mol-1, while the Polarizable Continuum Model (PCM) method with the Pliego and Riveros atomic cavities has led to RMS error of only 3.2 kcal mol-1. For methanol solvent, the SMD method has a RMS error of 3.0 kcal mol-1. The classical protic to dipolar aprotic solvent rate acceleration effect was not predicted by the SMD model for the tested systems.
TL;DR: In this article, a molecular modeling analysis via density functional theory has been performed on all possible conformers of acetaminophen and the optimized structures, total energies, energy gap, chemical potential, global hardness, softness, global electrophilicity and dipole moments were calculated.
19 May 2016
TL;DR: In this paper, the authors investigated how to control the rate of photoreduction of metastable AuCl2- at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size).
Abstract: This study investigated how to control the rate of photoreduction of metastable AuCl2– at the solid–solution interface of large ZnO nanoparticles (NPs) (50–100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO–Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2– at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO–solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent’s permittivity (e) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO–solution interface, it was confirmed that low e solvent mixtures (e ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 104 electrons·particle–1·s–1) compared to solvent mixtures with high e (e = 29.9, ∼1.9 × 104 electrons·particle–1·s–1). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO–Au NP hybrid. Under conditions where electron discharge was rapid (such as in low e solvents), AuCl2– precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.
TL;DR: In this article, the depolymerisation of an ammonia treated lignin to alkylphenols over a Pt/alumina catalyst was investigated under a range of process parameters including, pressure, mass of Lignin, solvent and gas atmosphere.
TL;DR: In this paper, the authors used a parallel video-recording of the angular displacements in four electrolytes with different solvents to identify solvent influence on the driving reactions.
Abstract: Full polymeric trilayer bending actuators are used as a tool to identify solvent influence on the driving reactions. The actuator’s structure includes two opposite polypyrrole-dodecylbenzene sulfonate (PPy-DBS) films interpenetrating a polyvinylidene fluoride (PVdF) central membrane placed between them. The actuators are electrochemically and electrodynamically characterized using parallel video-recording of the angular displacements in four electrolytes with different solvents. Actuation in aqueous (Aq) and ethylene glycol (EG) solutions occurs by reaction-driven exchange of cations while actuation in propylene carbonate (PC) and acetonitrile (AN) solutions is motivated by reaction-driven exchange of anions. The solvent changes the actuation mechanism from reaction-driven cation to reaction-driven anion exchanges. The attained results can be explained if a solvent dependent (different dielectric constants and dipolar moments) shift of the playing intra-molecular forces in those dense polymeric gels during reaction is considered. Reaction-driven ionic exchanges were corroborated by EDX analysis of the oxidized and reduced films. Whatever the solvent, the studied actuators are Faradaic polymeric motors (the described angle is a linear function of the reaction charge) with a large hysteresis due to cooperative osmotic and electroosmotic processes.
TL;DR: The results show that both solvent polarity and relative strength of the donor groups have significant impact on the electric properties, but more strikingly on the first hyperpolarizability β.
Abstract: We calculated the nonlinear optical properties of 24 azo-enaminone derivatives, incorporating solvent effects on their geometric and electronic structure, to assess the impact of the environment on these properties. Namely, we incorporated chloroform, tetrahydrofuran, acetone, ethanol, methanol, and dimethyl sulfoxide in our calculations and compared our results incorporating solvent effects with our gas-phase calculations. To account for the electron correlation effects on NLO properties, we performed the calculations at MP2/6-31G(p)//MP2/6-31G(d) level set. The polarizable continuum model was used to simulate the presence of the solvent. The exponents of p extra functions added to heavy atoms were obtained, imposing the maximization of the first hyperpolarizability. Two structural configurations (Z and E) of azo-enaminones were investigated to assess the isomeric effects of the electric properties. Our results show that both solvent polarity and relative strength of the donor groups have a significant i...
TL;DR: In this article, arylsulfenyl derivatives were synthesized in good yields by copper-catalysed cross-coupling reaction of arylthiols or diaryl diselenides with the commercially available 4,7-dibromobenzo[c][1,2,5]thiadiazole.
Abstract: Bis-arylsulfenyl- and bis-arylselanyl-benzo-2,1,3-thiadiazoles were synthesized in good yields by copper-catalysed cross-coupling reaction of arylthiols or diaryl diselenides with the commercially available 4,7-dibromobenzo[c][1,2,5]thiadiazole. The arylsulfenyl derivatives present absorptions in the visible region (∼420 nm) with molar absorptivity coefficient and radiative rate constant values ascribed to spin and symmetry allowed π–π* electronic transitions, with almost complete absence of solvatochromic effect. An emission located in the cyan green to green region (514–570 nm), with a large Stokes shift (90–146 nm) was observed, probably associated to the charge transfer character of the S1 state. Theoretical calculations were also performed in order to study the geometry, charge distribution and photophysical properties of the molecules in their ground and excited electronic states. TD-DFT calculations were performed using the PBE1PBE and CAM-B3LYP functionals with cc-pVDZ basis set for geometrical optimisations in the S0 and S1 states and jun-cc-pVTZ basis set to obtain vertical transition energies and electronic properties. Solvent effects were included by IEF-PCM formalism using solvents with different dielectric constants. The computationally predicted transition energies calculated with CAM-B3LYP are in good agreement with the experimental results. No substantial solvatochromic effect was found in the absorption maxima, but in the emission from S1 state a redshift was observed on increasing the solvent polarity. This fact, combined with higher dipole moment in the first excited state and some spatial separation of HOMO and LUMO orbitals could indicate an intramolecular charge transfer character of the S1 state.