General Solvent Effects Research Articles

Effect of positional substitution of amino group on excited state dipole moments of quinoline

The effect of positional substitution of amino group on the ground and excited state dipole moments of quinoline ring has been investigated using solvatochromic shift methods. The excited state dipole moments of 5aminoquinoline (5AQ) and 3aminoquinoline (3AQ) have been estimated from the spectral data in different non-polar, polar aprotic and polar protic solvents using Bakhshiev and Kawski–Chamma–Viallet equations. It has been observed that both grounds as well as excited state dipole moments for 5AQ are higher than those for 3AQ by approximately a factor of two. Higher values of the excited state dipole moments for both 3AQ and 5AQ as compared to corresponding ground state values have been attributed to intramolecular charge transfer processes. The role of specific solute–solvent interaction on excited state dipole moment in addition to the general solvent effects has been discussed.

Effect of Solvent Characteristics on the Photophysics of Hydroxyl Aromatic Compounds

The effect of solvent characteristics on the absorption and emission properties of 1- and 2-naphthols have been studied and the results interpreted in terms of the general and specific solute-solvent interactions. Measurements were performed in several solvents and analysis of the absorption and emission wavelengths were made using Lippert’s model for general solvent effects. A near linear relationship between the Stokes shift (\(\Delta\bar{\nu}\)) and the orientation polarizability (Δf) were observed for both 1- and 2-naphthols in most of the alkanols, thus showing evidence of a general solvent effect. However, in 1,4-dioxane–water mixtures the plots deviate from linearity indicating the dominance of specific solvent effects that are not included in Lippert’s equation. In the case of interactions between the fluorophores and dioxane–water mixtures, excess Stokes’ shifts are observed in the order of dioxane composition 10%>20%>30%>50%>60%>80%. This may be due to excited state proton transfer (ESPT) and the involvement of hydrogen bonding between the protic group of the fluorophore and the solvents.

Photophysical investigation of microenvironment in glycerol based dansylated polyether dendrons

Photophysical studies of four generations of polyglycerol dendrons with isopropylidene end groups and dansyl moiety as a fluorophore attached at the focal point were carried out. All the four generations showed similar behaviour in their absorption transitions but the emission maximum for all generations of dendrons showed strong dependence on the solvent polarity. The solvatochromic shift of emission maximum showed linearity in the Lippert–Mataga plot, indicating the dominant importance of general solvent effect in all generations of dendrons. Photophysical parameters such as fluorescence quantum yield, fluorescence lifetime and radiative decay rate constant showed solvent polarity dependence. The detailed photophysical study reveals that due to the increased influence of the repeating dendron units of the higher order dendrons on the dansyl microenvironment, it becomes less and less influenced by the solvent.

Carbazole Donor−Carbazole Linker-Based Compounds: Preparation, Photophysical Properties, and Formation of Fluorescent Nanoparticles

A new class of highly soluble and stable compounds (1-4) has been synthesized and characterized. Compounds 1, 2, and 3 have 3,6-disubstituted carbazole as electron-donor-linked through the 2,7-positions of N-substituted carbazole with variably substituted phenyl acetylenes as electron acceptors. Compound 4 has two identical donors linked through the 2,7-position of N-substituted carbazole. These compounds absorb from UV to visible region and emit intensely from blue to green. The effect on the photophysical properties of these compounds by changing acceptors while keeping the donor and linker constant has been studied. A study of solvent effects on their photophysical properties has shown that an increase in polarity of the solvent causes a reduction of fluorescence quantum yields. With a decrease in temperature, these compounds showed increased emission intensity accompanied by a red shift of emission. Edge excitation red shift showed as much as 128 nm for compound 2 in isopropanol. Solid-state fluorescence quantum yields vary from 0.27 to 0.68 for these compounds. The fluorescence lifetimes of these compounds are solvent dependent. Compound 2 showed remarkable change in emission with concentration. Compounds 2 and 3 form highly stable fluorescent organic nanoparticles (FONs) in tetrahydrofuran/water mixtures. The general and specific solvent effect on the emission properties of these compounds are investigated by Lipert-Mataga plots. The potentiality of these compounds for use in dye-sensitized solar cells and in organic light-emitting diodes is under study in our laboratories.

Concentration-Dependent Br···O Halogen Bonding between Carbon Tetrabromide and Oxygen-Containing Organic Solvents

High concentration-dependent halogen bonding, a specific solvent effect between carbon tetrabromide and oxygen-containing organic solvents, including methanol, ethanol, acetone, dioxane, diethyl ether, and tetrahydrofuran, was found to coexist with the general solvent effect when CBr4 was over 7.8 x 10(-3) M approximately 1.6 x 10(-2) M critical concentration range. In contrary, in less than this concentration range, only general solvent effect occurred. The 1:1 stoichiometry of halogen bonding complex between CBr4 and charge donor was testified using the modified Benesi-Hildebrand method. The Mulliken correlation confirmed the charge-transfer (CT) character of the CBr4/solvent associations. The electronic coupling elements (H(DA)) showed that the C-Br...O complexes are most-likely localized, which is named as outer-type complex. Density functional theory (DFT) calculation was performed to predict geometry, surface electrostatic potential, interaction energy, and vibrational frequency in gas phase. The MP2 method was also employed to calculate the formation of the sigma-hole (sigma(h)) bonding complexes between carbon tetrabromide and oxygen-containing organic solvents. The vertical excitation energies of the sigma(h)-bonding complexes were calculated by time-dependent density functional theory (TD-DFT). The experimental and theoretical results showed that sigma(h) bonding might be a more important factor for the halogen bonding complex investigated here than the CT. The results showed that Br...O halogen bonding is a blue-shift type.

Effect of solvent influence on J-aggregate of tetra- p-hydroxyphenylporphyrin (THPP) under different pH

In this paper, tetra- p-hydroxyphenylporphyrin (THPP) is dissolved in different solvents (chloroform, ethanol and N, N-dimethylformamide(DMF), Solvent effect is closely related to the nature and extent of solute–solvent interactions. Solvents have great influence on spectral characteristic and physicochemical processes of THPP. It is commonly acknowledged that solvent-dependent spectral shifts can arise from either general or specific solvent effects in the electronic transitions of solutes. For porphyrin, the solute–solvent interaction promotes conformational distortion of porphyrin plane in solution. Based on observed photophysical behavior in different polar solvent, the porphyrin can be grouped into “normal” and “perturbed” categories. The distortion of porphyrin plane causes redistribution of electron density, which changes the acid and basic properties of pyrrolic nitrogen atoms in the center of porphyrin ring. Furthermore, the solvent effects influence aggregate properties of porphyrin in solution. We confirm the results by the pH-titration experiment in the three solvent and investigate the difference of structure between J-aggregate and monomer by the Raman.

Features of absorption and fluorescence spectra of prodan

Some important and essential features of absorption and fluorescence spectra of prodan in homogeneous and binary mixes are studied. According to results obtained from experimental and quantum-chemical researches we show that the absorption spectrum of prodan in nonpolar solvent within 25,000–50,000 cm −1 is formed by eight electronic transitions. Quantum-chemical calculations are performed in the geometry of both the ground and exited states of prodan. The rate constants of photoprocesses and the quantum yield of fluorescence are determined for the prodan and its complexes with water. A dramatic shift of the fluorescence band at changing from nonpolar solvent to isopropyl alcohol and water is explained. The roles of general solvent effects and specific interactions are separated. According to values of molecular electrostatic potential and charges on atoms the centers of possible interaction of prodan with a solvent are obtained. Possible models of prodan complexes in water are offered. The results of quantum-chemical calculation for offered complexes of prodan in water are compared with those for the free prodan molecule. The presence of the second band (about 24,000 cm −1) in fluorescence spectra of prodan in isopropyl (ethyl) alcohol–water solvents is explained.

Insight into the solvent effect: A density functional theory study of cisplatin hydrolysis

The solvent effect on reactions in solutions is crucial for many systems. In this study, the reaction barrier with respect to the number of solvent molecules included in the system is systematically studied using density function theory calculations. Our results show that the barriers rapidly converge with respect to the number of solvent molecules. The solvent effect is investigated by calculating cisplatin hydrolysis in several types of solvents. The results are analyzed and a linear relationship between the reaction barrier and the interaction strength of solvent-reactants is found. Insight into the general solvent effect is obtained.

Theoretical Studies of the Aminolysis for N‐Methyl β‐Sultam in Solution

AbstractThe aminolysis and the effect of water on the aminolysis processes of n‐methyl β‐sultam have been studied using density functional theory (DFT) method at the B3LYP/6‐31G* level. The stationary structures and energies have been investigated for both reactions to find two different reaction channels. Specific and general solvent effects have been evaluated and the most favored pathway was found. The presence of solvent disfavors the reaction, whereas the participation of water in the aminolysis reaction plays a positive role and reduces the activation energy greatly. All transition states in the assisted aminolysis are 35–70 kJ/mol lower than those for the non‐assisted reaction.

General and Specific Solvent Effects in Optical Spectra of ortho-Aminobenzoic Acid

We describe studies about solvent effects on the absorption and emission properties of o-aminobenzoic acid (o-Abz), interpreting the results within the framework of general and specific solute-solvent interactions. Measurements were performed in several solvents and analysis of the absorption and emission wavelengths were made based on Lippert's model for general solvent effects and on the use of different parameters to describe the ability of the solvent to promote specific interactions with the solute. We observed low sensitivity of the Stokes shift upon changes in the medium polarity, and large deviation from the linearity predicted by Lippert's equation when the solvents were characterized as Bronsted acid in the Kamlet-Taft pi* scale. Quantum yield and fluorescence lifetimes were best interpreted based on the AN+DN scale used to describe the electron donor/acceptor properties of the solvent. The results indicated that non-radiative deexcitation processes are favoured in solvents which promote the formation of intramolecular hydrogen bond, while interactions with electron acceptor solvents lead to enhancement of fluorescence.

Solvatochromic Fluorescence Behavior of 8-Aminoquinoline-Benzothiazole: A Sensitive Probe for Water Composition in Binary Aqueous Solutions

Solvatochromic fluorescence behavior of 8-aminoquinoline based benzothiazole derivative in varying solvent systems has been investigated. Benzothiazole appended 8-aminoquinoline 3 showed distinctive fluorescence color changes depending upon the solvent polarities and the fluorescence color changes occurred over relatively wide span in visible region from 486 nm to 598 nm which can be detected with naked eye. Compound 3 also exhibited significant spectral shifts in <TEX>${\lambda}_{em}$</TEX> as a function of water composition in binary aqueous solvent systems. The changes are due to the specific interaction of 3 by hydrogen bonding with water as well as general solvent effect. The observed solvatochromic fluorescence characteristics of 3 could be used as a new probe for the micro-environmental polarity changes as well as a sensitive sensor for the determination of water composition in binary aqueous solutions.

First reported evidence that solvent polarity induces an [formula omitted] inversion in the indole chromophore

The solvatochromism of indole in 26 pure solvents, 21 binary solvent mixtures, and the gas phase was determined. The description of the solvatochromism of indole in the light of the SPP, SB, and SA scales allowed us to derive the first reported evidence that the inversion in its first two excited electronic states is caused by an increase in the general solvent effect. Based on the results, indole only emits from its 1 L a state in solvents with SPP>0.8 and from its 1 L b state in solvents with SPP<0.8.

Computational studies of the aminolysis of oxoesters and thioesters in aqueous solution

Transition state structures and energies have been investigated for concerted and stepwise mechanisms for the acyltransfer reactions of ethyl acetate and ethyl thioacetate with ammonia. Specific and general solvent effects have been evaluated. The results predict stepwise mechanisms involving water-catalyzed proton transfer for both reactions and indicate that the thioester is more reactive than the oxoester in both the addition and elimination steps.

CASSCF Investigation of Electronic Excited States of 2-Aminopurine

2-Aminopurine is a highly fluorescent analogue of adenine that can be incorporated synthetically into DNA with little perturbation of the native double-helical structure. The sensitive dependence of the quantum yield of this fluorophore on nucleic acid conformation has made it an invaluable probe of DNA structure, dynamics, and interactions. To assist in the development of models for the molecular interpretation of fluorescence measurements, the electronic structure of 2-amino-9-methylpurine has been calculated in the ground state and the lowest singlet ππ* and nπ* excited states. These computations employed the complete active space multiconfigurational self-consistent field method (CASSCF), supplemented by multiconfigurational quasi-degenerate perturbation theory (MCQDPT). The predicted energies for ππ* excitation and emission and nπ* excitation are in good agreement with previous experimental values. The permanent molecular dipoles of the ground and ππ* excited states are similar in magnitude and direction, consistent with experimental observations of weak solvatochromic shifts in ππ* absorption and emission spectra. However, the permanent dipole of the nπ* state is rotated approximately 60° relative to that of the ground state, implying that the nπ* excitation energy will increase in more polar solvents due to the relative destabilization of this state by unfavorably oriented solvent dipoles. This result demonstrates that the “blue-shift” of the nπ* state in polar solvents, which is commonly attributed to the effect of hydrogen bonding, can arise entirely from a general solvent effect. The energy of a radiationless vibronic transition from the ππ* state to the nπ* state will increase in more polar solvents, provided that the solvent does not rearrange during the transition. Consequently, the efficiency of fluorescence quenching by vibronic coupling between the ππ* and nπ* states is predicted to decrease significantly in such solvents. The geometry of the fluorescent emitting state, obtained by CASSCF optimization of the ππ* state, is moderately buckled due to the occupation of an antibonding orbital localized to C6. This buckling implies an out-of-plane vibration during the relaxation of the ππ* state, which is required for vibronic coupling between this state and the nπ* state. Such a solvent-sensitive intramolecular quenching mechanism may account for the observed dependence of the fluorescence lifetime of 2-aminopurine on the local environment both in pure solvents and in DNA.

Environmental effects on the photophysics of pyrromethene 556

Visible absorption and fluorescence (steady-state and time-correlated) spectroscopies were applied to study the photophysics of the dye pyrromethene 556 in liquid solutions. Environmental factors, such as dye concentration, pH and nature of the solvent, were considered. The shape of the absorption spectrum does not change with the dye concentration, suggesting that the dye does not aggregate up to the solubility limit. The changes in the fluorescence signal by increasing the dye concentration (shift to lower energies in the fluorescence band and decrease/increase in the fluorescence quantum yield/lifetime) are attributed to re-absorption and re-emission effects. The solvent effects are analysed in terms of multicomponent linear regressions in which several solvent parameters (dipolarity/polarizability, H-bond donor, electron donor capacities, etc.) are individually and simultaneously treated. The influence of the solvent on the maximum of the absorption and fluorescence bands and on the rate constant of the radiative deactivation is explained on the basis of the stabilization of several resonance structures of the chromophore by general solvent effects and by specific solute–solvent interactions.

Fluorescence properties of a new guanosine analog incorporated into small oligonucleotides

The fluorescence properties of 3-methyl-isoxanthopterin (3-MI) incorporated into different oligonucleotides have been determined. This highly fluorescent guanosine analog has its absorption and fluorescence spectra well resolved from those of the normal nucleotides and the aromatic amino acids. The small shifts observed in absorption and fluorescence emission spectra upon incorporation of 3-MI into these oligonucleotides are consistent with a general solvent effect and do not suggest any contribution from the position of the probe from the 5' end, the sequence of nucleotides immediately 5' or 3' to the probe, or the single- or double-stranded nature of the oligomer. However, steady-state and time-resolved fluorescence studies indicate that the presence of a purine immediately 5' or 3' to the probe results in some dynamic but mostly static quenching in the single-stranded oligomer. Furthermore, a 3' purine is more effective than a 5' purine, and an adenine appears to be more effective than a guanine for these static quenching interactions. Formation of the double-stranded oligomer leads to an additional loss of quantum yield, which can also be ascribed primarily to static quenching. These results show that this new class of spectrally enhanced fluorescent purine analogs will be able to provide useful information concerning the perturbation of nucleic acid structures.

Synthesis and Spectroscopic Characterization of 1-Bromo-(4-bromoacetyl)naphthalene. A Thiol-Reactive Phosphorescent Probe

The synthesis and chemical end spectroscopic characterization of 1-bromo-4-(bromoacetyl)naphthalene (BBAN), a thiol-reactive phosphorescent probe, is described. The energy and shape of the near-ultraviolet n-π * absorption bend of BBAN in simple solvents, mixed solvents, end within certain biomolecular complexes are shown to be sensitive to both general and specific solvent effects. Anoxic solutions of BBAN exhibit strong structured phosphorescence emission with little, if zny, prompt fluorescence, suggesting that an efficient intersystem crossing mechanism exists within the molecule(...)

Effect of physico-chemical properties of binary liquid membranes on steady-state transport of copper(II) ions

The coupled transport of copper(II) ions by the carrier Acorga P-50 through mono and binary liquid membranes has been analysed in the steady-state approximation. The membranes were composed of C 8-C 14 normal chain paraffins and their mixtures. It was found that the total ion fluxes are the most appropriate kinetic parameters for asymmetric membranes in the steady-state approximation. The results obtained for single component (mono) membranes have shown the importance of the physicochemical nature of membrane material. In all cases transport rates were diminished by increasing viscosity and by increased copper(II)-carrier-membrane interactions, as governed by general solvent effects (polarity and polarizability). Using binary solvent mixtures as the membrane a surprising variety of substitution profiles have been obtained, despite the very similar chemical character of the membrane components. The regular substitution profile obtained for the n-octane ( S)-n-tetradecane ( Z) solvent pair could be analysed successfully by COPS theory. The results confirmed quantitatively the decisive role played by molecular interactions in transport kinetics. A simple molecular model is proposed to explain the dominating roe played by membrane polarity in determining transport rates. The general conclusions support fully those obtained previously for non-steady state inetic conditions.

Membrane material effect on copper coupled transport through liquid membranes

The influence of the physico-chemical properties of the membrane material on coupled transport of Cu(II) is investigated using light organic solvents belonging to different solvent classes. The kinetics of transport could be analyzed in the formalism of two consecutive irreversible first order reactions. The rate determining step is the diffusion across the membrane boundary layer. Detailed analysis allowed to determine the conditions required for steady-state transport. Permeation rates turn out to be less sensitive to medium effects than membrane exit rates. In all cases general solvent effects (polarity, polarizability) dominate the observed kinetics without excluding completely specific effect (π-donor ability). The results suggest that medium effects influence more the initial state than the transition state of diffusion. Among the solvents used open-chain paraffins appear to be the most efficient membrane materials.

Fluorescence properties of methyl 8-(2-anthroyl) octanoate, a solvatochromic lipophilic probe

Fluorescence excitation and emission spectra, relative fluorescence quantum yield φ r and fluorescence lifetime τ of methyl 8-(2-anthroyl)-octanoate have been studied in a set of organic solvents covering a large scale of polarity and in the presence of water. In this probe, the 2-anthroyl chromophore exhibits quite remarkable and unique fluorescence properties. Thus, when going from n-hexane to methanol, the maximum emission wavelength λ em max shifts from 404 nm to 492 nm while φ r and τ increase from 1 to 17.7 and from 0.91 ns to 13.5 ns, respectively. These increments are still more accentuated in the presence of water with estimated values of 526 nm for λ em max, 27 for φ r and 20 ns for τ in this solvent. Because of the presence of a keto group which is a hydrogen bond acceptor and which can conjugate with the aromatic ring so as to provide the chromophore with a high dipole moment, the fluorescence properties of the probe strongly depend on the polarity of the surrounding medium. They can be accounted for in terms of general solvent effects (dipolar solute/solvent interactions) in the presence of aprotic solvents and in terms of specific solvent effects (hydrogen bonding) in protic solvents. Such properties of solvatochromism make the 2-anthroyl chromophore, after 8-(2-anthroyl)octanoic acid has been attached to phospholipids (E. Perochon and J.F. Tocanne (1991) Chem. Phys. Lipids 58, 7–17) a potential tool for studying microenvironmental polarity in biological membranes.